PREPARATION AND MODIFICATION OF VARIOUS ADSORBENTS …
260
i PREPARATION AND MODIFICATION OF VARIOUS ADSORBENTS FROM RICE HUSK AND THEIR USE FOR THE REMOVAL OF TOXIC DYES AND HEAVY METAL IONS FROM AQUEOUS MEDIA BY ABDUL MALIK 15-S-AWKUM-USM-PHD-PHYCHE-1 Thesis submitted to the Abdul Wali Khan University Mardan in the partial fulfillment of the requirements for the degree of PhD IN CHEMISTRY Supervisor Dr. Abbas Khan DEPARTMENT OF CHEMISTRY FACULTY OF CHEMICAL AND LIFE SCIENCES ABDUL WALI KHAN UNIVERSITY MARDAN, PAKISTAN (2019)
Transcript of PREPARATION AND MODIFICATION OF VARIOUS ADSORBENTS …
i
PREPARATION AND MODIFICATION OF VARIOUS
ADSORBENTS FROM RICE HUSK AND THEIR USE FOR THE
REMOVAL OF TOXIC DYES AND HEAVY METAL IONS FROM
AQUEOUS MEDIA
BY
ABDUL MALIK
15-S-AWKUM-USM-PHD-PHYCHE-1
Thesis submitted to the Abdul Wali Khan University Mardan in the partial fulfillment of
the requirements for the degree of
PhD IN CHEMISTRY
Supervisor
Dr. Abbas Khan
DEPARTMENT OF CHEMISTRY
FACULTY OF CHEMICAL AND LIFE SCIENCES
ABDUL WALI KHAN UNIVERSITY MARDAN, PAKISTAN
(2019)
ii
PREPARATION AND MODIFICATION OF VARIOUS
ADSORBENTS FROM RICE HUSK AND THEIR USE FOR THE
REMOVAL OF TOXIC DYES AND HEAVY METAL IONS FROM
AQUEOUS MEDIA
Submitted By: Supervisor:
Abdul Malik Dr. Abbas Khan
15-S-AWKUM-USM-PHD-PHYCHE-1 Associate Professor
PhD in Physical Chemistry Department of Chemistry,
Abdul Wali Khan University, Mardan
DEPARTMENT OF CHEMISTRY
FACULTY OF CHEMICAL AND LIFE SCIENCES
ABDUL WALI KHAN UNIVERSITY MARDAN, PAKISTAN
(2019)
iii
Author‟s Declaration
I Abdul Malik hereby state that my PhD thesis entitled ―Preparation and Modification of
Various Adsorbents from Rice Husk and Their Use for the Removal of Toxic Dyes and
Heavy Metal Ions from Aqueous Media” is my own work and has not been submitted
previously by me for taking any degree from this University (Abdul Wali Khan University
Mardan, Pakistan), or anywhere else in the country/world.
At any time if my statement is found to be incorrect even after my Graduate the university has the
right to withdraw my PhD degree in Physical Chemistry.
__________
Abdul Malik
iv
Plagiarism Undertaking
I solemnly declare that research work presented in the thesis titled ―Preparation and
Modification of Various Adsorbents from Rice Husk and Their Use for the Removal of Toxic
Dyes and Heavy Metal Ions from Aqueous Media” is solely my research work with no
significant contribution from any other person. Small contribution/help wherever taken has been
duly acknowledged and that complete thesis has been written by me.
I understand the zero tolerance policy of the HEC and University. (Abdul Wali Khan University
Mardan, Pakistan) towards plagiarism.
Therefore I as an Author of the above titled thesis declare that no portion of my thesis has been
plagiarized and any material used as reference is properly referred/cited.
I undertake that if I am found guilty of any formal plagiarism in the above titled thesis even after
award of PhD degree, the University reserves the rights to withdraw/revoke my PhD degree and
that HEC and the University has the right to publish my name on the HEC/University Website on
which names of students are placed who submitted plagiarized thesis.
____________
Abdul Malik
v
Certificate of Approval
This is to certify that the research work presented in this thesis, entitled: “Preparation and Modification
of Various Adsorbents from Rice Husk and Their Use for the Removal of Toxic Dyes and Heavy
Metal Ions from Aqueous Media” was conducted by Mr. Abdul Malik under the supervision of Dr.
Abbas Khan Associate Professor Department of Chemistry AWKUM. No part of this thesis has been
submitted anywhere else for any other degree. This thesis is submitted to the Directorate of Academics
and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Field of
Physical Chemistry, Department of Chemistry Abdul Wali Khan University Mardan.
Student Name: Mr. Abdul Malik Signature: _____________________
Examination Committee:
External Examiner: ____________________
Prof. Dr. Abdul Naeem Khan
NCE Physical Chemistry
University of Peshawar, Peshawar
Supervisory Committee
Dr. Abbas Khan Dr. Momin Khan
Supervisor/Associate Professor Member/Associate Professor
Department of Chemistry, AWKUM Department of Chemistry, AWKUM
Dr. Khair Zaman Prof. Dr. Zahid Hussain
Member/Associate Professor Chairman/Internal Examiner
Department of Chemistry, AWKUM Department of Chemistry, AWKUM
Dean, Faculty of Chemical and Life Sciences
Director Academics & Research
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TABLE OF CONTENTS
S. No. CONTENTS Page No.
Chapter 1 INTRODUCTION 1
1.1 Classification of Dyes 2
1.2 Classification Based on Origin 2
1.2.1 Plant-Origin 2
1.2.2 Animal-Origin 2
1.2.3 Mineral-Origin 2
1.2.3.1 Red-Pigments 3
1.2.3.2 Yellow-Pigments 3
1.2.3.3 Green Pigments 3
1.2.3.4 Blue-Pigments 3
1.2.3.5 White Pigments 3
1.2.3.6 Black-Pigments 4
1.3 Classification Based on Application Methods 4
1.3.1 Organic Dyes 4
1.3.2 Acid Dyes 4
1.3.3 Basic-Dyes 4
1.3.4 Direct Dyes 5
1.3.5 Mordant-Dyes 5
1.3.6 Vat-Dyes 5
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1.3.7 Azoic Dyeing 5
1.3.8 Specific Applications of Dyes 6
1.4 Classification Based on Chromophores 6
1.5 Major Groups 7
1.5.1 Natural Dyes 8
1.5.2 Synthetic-Dyes 8
1.6 Effect of Dyeing Industrial Waste Matter on vegetation 8
1.7 Chemistry of Dyes 9
1.7.1 Basis for Color 9
1.7.2 Dyes Versus Pigments 10
1.7.3 Dye-Substrate Affinity 10
1.7.4 Dyes Used for Polyamides/Proteins 11
1.7.5 Dyes Used for Cationic-Polymer 11
1.7.6 Dyes Used for Cellulosic-Polymer 12
1.7.7 Toxicological Considerations 12
1.8 Waste Water 12
1.8.1 Acid Mine Drainage (AMD) 13
1.8.2 Complex Organic Chemicals Industry 13
1.8.3 Electric Power Plants 13
1.8.4 Food Industries 13
1.8.5 Iron/Steel ‗Industry‘ 14
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1.8.6 Pulp/Paper Industries 14
1.8.7 Industrial Oil Contamination 15
1.8.8 Black-Water 15
1.8.9 Determination of Adsorbable Organic Halides (AOX) 15
1.8.10 Biochemical Oxygen Demand (BOD) 15
1.8.11 Total Dissolved Solids (TDS) 16
1.8.12 Total Suspended‘ Solids (T.S.S) 16
1.9 Waste Water Treatment Options 16
1.9.1 Activated Sludge 16
1.9.2 API Oil–Water Separator 17
1.9.3 Ozonation 17
1.9.4 Chloramination 17
1.9.5 Chlorination, Bromination and Iodinization 17
1.9.6 Home Filtration 17
1.9.7 Clarifier 18
1.9.8 Facultative lagoon 18
1.9.9 Molecular Encapsulation 18
1.9.10 Membrane Bioreactor (MBR) 18
1.9.11 Reverse Osmosis 19
1.9.12 Sedimentation 19
1.10 Heavy Metals 19
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1.10.1 Toxic Heavy Metals 20
1.10.2 History of Toxic Heavy Metals 20
1.10.3 Arsenic (As) 20
1.10.4 Mercury 20
1.10.5 Lead 20
1.10.6 Chromium 21
1.10.7 Cadmium 21
1.10.8 Toxic Effects of Heavy Metals 21
1.11 Objectives 23
Chapter 2 LITERATURE REVIEW 24
Chapter 3 EXPERIMENTAL 40
3.1 Materials 40
3.2 Preparation of Adsorbents from Rice Husk 41
3.2.1 Preliminary Treatment of Rice Husk (RH) for the Preparation of
Adsorbents 41
3.2.2 Preparation of ‗Rice Husk Char‘ (RHC) 42
3.2.3 Preparation of KOH Modified Rice Husk Char (KMRHC) 42
3.2.4 Preparation of Rice Husk Ash (RHA) 42
3.2.5 Preparation of KOH Modified Rice Husk Ash (KMRHA) 43
3.3 Adsorbate 43
3.4 Adsorption Experiments for the Investigation of Dye 44
3.4.1 ‗Equilibrium Study
‘ 44
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3.4.2 Effect of ‗Adsorbent Dose‘ on Adsorption of Dye 44
3.4.3 Effect of pH on ‗Adsorption‘ of Dye 44
3.4.4 Effect of ‗Temperature‘ on Adsorption of Dye‘ 45
3.5 Adsorption Experiments for the Investigation of Metal Ions 45
3.5.1 Equilibrium Study of the Adsorption of ‗Metal Ions‘ 45
3.5.2 Effect of ‗Adsorbent Dose‘ on Adsorption‘ of (Pb2+
) 45
3.5.3 Effect of ‗pH‘ on Adsorption of Metal Ions on Adsorbent 46
3.5.4 Effect of ‗Temperature‘ on Adsorption of Pb
2+on Adsorbent 46
3.6 Characterization 46
3.6.1 UV–Visible Spectrophotometric Analysis 46
3.6.2 Flame Atomic Absorption Spectroscopy ‗FAAS‘ 46
3.6.3 Scanning Electron Microscopy ‗SEM‘ 47
3.6.4 X-ray Diffractometry ‗XRD‘ 47
3.6.5 Fourier Transform Infrared Spectrometry ‗FT-IR‘ 47
Chapter 4 ESULTS AND DISCUSSIONS 48
4.1 UV,-Visible Spectroscopy of Representative Samples 48
4.2 Scanning Electron Microscope (SEM) Studies 48
4.3 ‗Energy Dispersive X-Ray
‘‗EDX‘ Analysis 57
4.4 ‗X-Ray Diffraction‘ ‗XRD‘ Analysis 62
4.5 FT-IR Spectral Analysis 65
4.6
Effect of Temperature on the Activation of RHC, KMRHC, RHA
and KMRHA 71
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4.7
Adsorption of Orange G (OG) Dye on RHC, KMRHC, RHA and
KMRHA 74
4.7.1
‗Effect of
‗Contact Time on ‗Adsorption of OG on RHC,
KMRHC, RHA and KMRHA 74
4.7.2
Effect of ‗Adsorbent Dose‘ on Adsorption of OG on RHC,
KMRHC, RHA and KMRHA 81
4.7.3
Effect of ‗Dye Concentration
‘ on Adsorption of OG on RHC,
KMRHC, RHA and KMRHA 86
4.7.4
‗Effect of pH
‘ on Adsorption of OG Dyes on RHC, KMRHC,
RHA and KMRHA 93
4.7.5
‗Effect of Temperature
‘ on Adsorption of OG Dye on RHC,
KMRHC, RHA and KMRHA 98
4.7.6 ‗Thermodynamic Studies‘ 103
4.7.7 Adsorption Kinetics 106
4.7.8 Adsorption Isotherm Models 109
4.7.8.1 ‗Langmuir Adsorption Isotherm Model
‘ 109
4.7.8.2 ‗Freundlich Isotherm Model
‘ 109
4.7.8.3 The Temkin Adsorption Isotherm Model 110
4.8
Adsorption of Titan Yellow (TY) Dye on RHC, KMRHC, RHA
and KMRHA 115
4.8.1
Effect of ‗Contact Time on Adsorption‘ of TY Dye on RHC,
KMRHC, RHA and KMRHA 115
4.8.2
Effect. of Adsorbent-
.Dose on Adsorption of TY on RHC,
KMRHC, RHA and KMRHA 122
4.8.3
‗Effect of Dye Concentration
‘ on Adsorption of TY on RHC,
KMRHC, RHA and KMRHA 127
4.8.4
Effect of ‗pH on Adsorption‘ of TY Dye on RHC, KMRHC, RHA
and KMRHA 134
vii
4.8.5 ‗Effect of Temperature‘ on Adsorption of TY Dye on RHC,
KMRHC, RHA and KMRHA 141
4.8.6 ‗Thermodynamic Studies‘ 146
4.8.7 Adsorption Kinetics of TY 149
4.8.8 Adsorption Isotherm Models for TY 152
4.9 Adsorption of Pb2+
on RHC, KMRHC, RHA and KMRHA 157
4.9.1
Time Optimization Study for Adsorption of Pb2+
on RHC,
KMRHC, RHA and KMRHA-Adsorbents 157
4.9.2 ‗Effect of Adsorbent Dose‘ on Adsorption of Pb
2+ on RHC,
KMRHC, RHA and KMRHA-Adsorbents 163
4.9.3
‗Effect of Pb
2+. Conc. on ‗Adsorption of Pb
2+‘ on RHC, KMRHC,
RHA and KMRHA 168
4.9.4
Effect of pH on the Adsorption of Pb2+
on RHC, KMRHC, RHA
and KMRHA-Adsorbents 175
4.9.5
Effect of ‗Temperature on Adsorption of Pb
2+‘ on RHC,
KMRHC, RHA and KMRHA-Adsorbents 179
4.9.6 ‗Thermodynamic Studies 183
4.9.7 ‗Adsorption Kinetics‘ of Pb
2+ 184
4.9.8 Adsorption Isotherm Model s for Pb2+
187
4.10 Comparative Study 192
Conclusions 194
Future Recommendations 195
References 196
List of Publications 225
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List of Figures
Fig. No. Title Page No.
1.1 Significance of Chromophore in A Conjugated-System 10
1.2 Conjugated-Systems Present in Vitamin A and Β-Carotene. 10
1.3 Ionic Interaction of Dye with the Substrate 11
1.4 Structures of a Commercial Acid and Cationic (Basic) Dye 11
1.5 Reductive-Cleavage of Direct-Red-28 (1) Using Azo-Reductase
Enzyme 12
3.1 Structural Formula of Orange G Dye 40
3.2 Structural Formula of Titan Yellow Dye 41
4.1
UV-,Visible Spectra for (A) Original OG Dye Solution (80mg/L) (B)
Residual Dye Conc. after Adsorption on RHA (C) Residual Dye Conc.
after Adsorption on RHC (D) Residual Dye Conc. after The Adsorption
on KMRHA (E) Residual Dye Conc. after the Adsorption on KMRHC.
50
4.2
UV Visible Spectra, for (A) Original TY Dye Solution (80mg/L) (B)
Residual Dye Conc. after Adsorption on RHA (C) Residual Dye Conc.
after Adsorption on RHC(D) Residual Dye Conc. after the Adsorption
on KMRHA (E) Residual Dye Conc. after the Adsorption on KMRHC.
51
4.3
Scanning Electron Micrograph‘ ―SEM‖ of, (A) Rice Husk Char, (B)
Orange G Dye Loaded Rice Husk Ash 52
4.4
Scanning Electron Micrograph‘ ―SEM‖ of, (A) KOH Modified Rice
Husk Char, (B) Orange G Dye Loaded KOH Modified Rice Husk har. 53
4.5
Scanning Electron Micrograph‘ ―SEM‖ of, Pb Loaded KOH Modified
Rice Husk Char 54
4.6
Scanning Electron Micrograph‘ ―SEM‖ of (A) RHA, (B) Pb Loaded
RHA 55
4.7 „Scanning Electron Micrograph
‘ ―SEM‖ of, (A) KMRHA, (B) Pb 56
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Loaded KMRHA
4.8
Energy Dispersive X-Ray‘ (EDX) Analysis Spectra of: (A) RHC,(B)
TY Dye Loaded RHA 58
4.9
„Energy Dispersive X-Ray
‘ Analysis Spectra of: (A
‘) RHA,(B
‘) Pb
Loaded RHA 59
4.10
Energy Dispersive X-Ray ‗Analysis Spectra of: (A) KMRHC,(B)TY
Dye Loaded KMRHC,(C) Pb Loaded KMRHC. 60
4.11
Energy Dispersive X-Ray‘ Analysis Spectra of: (A) KMRHA,(B)TY
Dye Loaded, KMRHA,(C) Pb Loaded KMRHA 61
4.12 XRD Pattern of: (A) RHC, (B) KMRHC 63
4.13 XRD Pattern of: (A) RHA (B) KMRHA 64
4.14
FTIR Spectra of: (A) RHC, (A) Pb Loaded RHC, (C) TY Loaded RHC
and (D) OG Load RHC 67
4.15
FTIR Spectra of: (A) KMRHC, (B) Pb Loaded KMRHC, (C) TY
Loaded KMRHC and (D) OG Load KMRHC 68
4.16
FTIR Spectra of: (A) RHA, (B) Pb Loaded RHA, (C) TY Loaded RHA
and (S) OG Load RHA 69
4.17
FTIR Spectra of: (A) KMRHA, (B) Pb Loaded KMRHA, (C) TY
Loaded KMRHA and (D) OG Load KMRHA 70
4.18 „Effect of Temperature
‘ on the Activation of RHC & KMRHC. 73
4.19
Adsorption of Orange G (OG) Dye on RHC, KMRHC, RHA and
KMRHA 74
4.20
Effect of Agitation Time on Percent Adsorption of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media, Experimental
Conditions were: pH = 4, T = 303K, Adsorbent Concentration = 2g/L,
C0= 80 mg/L
75
4.21
Effect of stirring Time on Uptake Capacity (mg/g) of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH= 4, T = 303K, Adsorbent Concentration = 2g/L,
76
x
C0= 80 mg/L
4.22
Effect of ‗Adsorbent Dose
‘ on the Uptake Capacity (mg/g) of OG on
RHC, KMRHC, RHA and KMRHA from Aqueous Media.
Experimental Conditions were: pH = 4, T = 303K, C0= 80 mg/L
82
4.23
Effect of ‗Adsorbent Dose‘ on the %age Removal of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions: pH = 4, T = 303K, C0= 80 Mg/L
83
4.24
Effect of Initial Dye Concentration‘ on the Uptake Capacity, of OG on
RHC, KMRHC, RHA and KMRHA from Aqueous Media.
Experimental Conditions were: pH = 4, T = 303K, Adsorbent
Concentration = 2g/L,
87
4.25
„Effect of Initial Dye Concentration
‘ on %
‗Adsorption
‘ of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 4, T = 303K, Adsorbent Concentration = 2g/L,
88
4.26
„Effect of pH
‘ on Uptake Capacity (mg/g) of OG on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions
were: Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
94
4.27
„Effect of pH
‘ on % Adsorption of OG on RHC, KMRHC, RHA and
KMRHA from Aqueous Media. Experimental Conditions were:
Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
95
4.28
„Effect of Temperature
‘ on Uptake Capacity (mg/g) of OG on RHC,
KMRHC, RHA And KMRHA from Aqueous Media. Experimental
Conditions were: Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
99
4.29
„Effect of Temperature‘ on% Removal of OG on RHC, KMRHC, RHA
and KMRHA from Aqueous Media. Experimental Conditions were:
Adsorbent Dose = 2g/L, T = 303K, C0= 80 Mg/L
100
4.30
Plots of ΔG Vs Temperature for the Adsorption OG on RHC, KMRHC,
RHA and KMRHA from Aqueous Media at Co= 80 mg/L 104
4.31
Pseudo-.First Order Kinetic‘ Models for Adsorption of OG on RHC,
KMRHC, RHA and KMRHA-Adsorbents 107
xi
4.32
Pseudo-.Second Order Kinetic Models for Adsorption of OG on RHC,
KMRHC, RHA and KMRHA-Adsorbents 108
4.33
Langmuir Models for Adsorption of OG on RHC, KMRHC, RHA and
KMRHA-Adsorbents 111
4.34
Freundlich Isotherm models for Adsorption of OG on RHC, KMRHC,
RHA and KMRHA-Adsorbents 112
4.35
Temkin Isotherm Models for‘ Adsorption of OG, on RHC, KMRHC,
RHA and KMRHA-Adsorbents 113
4.36
Effect of ‗Contact Time‘ on the Uptake‘ Capacity (mg/g) of TY on
RHC, KMRHC, RHA and KMRHA from Aqueous Media,
Experimental Conditions were; pH = 4, T = 303K, Adsorbent
Concentration = 2g/L, C0= 80 mg/L
116
4.37
Effect of ‗Contact Time‘ on %.Adsorption of TY on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions
were: pH = 4, T = 303K, Adsorbent Concentration = 2g/L, C0= 80
mg/L
117
4.38
Effect of Adsorbent.-Dose on the Uptake Capacity (mg/g) of TY on
RHC, KMRHC, RHA and KMRHA from Aqueous Media.
Experimental Conditions were: pH = 3.5, T = 303K, C0 = 80 mg/L
123
4.39
Effect of Adsorbent-.Dose on the %
.Adsorption of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 4, T = 303K, C0 = 80 mg/L
124
4.40
Effect of ‗Initial Dye Concentration
‘ on Uptake Capacity of TY on
RHC, KMRHC, RHA and KMRHA from Aqueous Media.
Experimental Conditions were; pH = 3.5, T = 303K, Adsorbent
Concentration = 2g/L
128
4.41
Effect of ‗Initial Dye Conc.‘ on %.Adsorption of TY on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions
were: pH = 3.5, T = 303K, Adsorbent Concentration = 2g/L
129
4.42 ‗Effect of pH‘ on the Uptake Capacity (mg/g) of TY on RHC, KMRHC, 135
xii
RHA and KMRHA from Aqueous Media. Experimental Conditions
were: Adsorbent dose = 2g/L, T = 303K, C0 = 80 mg/L
4.43
‗Effect of pH‘ on the %.Adsorption of TY on RHC, KMRHC, RHA and
KMRHA from Aqueous Media. Experimental Conditions were:
Adsorbent Dose = 2g/L, T = 303K, C0 = 80 mg/L
136
4.44
‗Effect of Temperature‘ on the Uptake Capacity. (mg/g) of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
142
4.45
‗Effect of Temperature, on the %
.Removal of TY on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions
were: Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
143
4.46
Plots of ΔG Vs Temperature for the Adsorption TY on RHC, KMRHC,
RHA and KMRHA from Aqueous Media at Co = 80 mg/L 147
4.47
Pseudo.-First Order
, Kinetic Models for Adsorption of TY on RHC,
KMRHC, RHA and KMRHA-Adsorbents 150
4.48
Pseudo.-Second Order Kinetic Models for the Adsorption of OG on
RHC, KMRHC, RHA and KMRHA-adsorbents 151
4.49
Langmuir Models for Adsorption of TY on RHC, KMRHC, RHA and
KMRHA-Adsorbents 153
4.50
Freundlich Isotherm for Adsorption of TY on RHC, KMRHC, RHA
and KMRHA-Adsorbents 154
4.51
Temkin Isotherms for Adsorption of TY on RHC, KMRHC, RHA and
KMRHA-Adsorbents 155
4.52
Time Optimization Study for the Adsorption Capacity of Lead Ions on
RHC, KMRHC, RHA, KMRHA. Co = 250 mg/L, pH = 6, Temp =
303K,
158
4.53
Time Optimization Study for the %.Adsorption of Lead Ions on RHC,
KMRHC, RHA, KMRHA, Co = 250 mg/L, pH = 6, Temp = 303K, 159
4.54
Effect of Adsorbent.-Dose on Adsorption Capacity of Pb
2+ on RHC,
KMRHC, RHA and KMRHA-Adsorbents 164
xiii
4.55
Effect of Adsorbent-.Dose on % Adsorption of Pb
2+ on RHC, KMRHC,
RHA and KMRHA-Adsorbents 165
4.56
Concentration Optimization Study for Adsorption Capacity of lead Ions
on RHC, KMRHC, RHA and KMRHA, Adsorbent Dose = 2g/L pH =
6, Temp = 303K, Agitation Time = 50min
169
4.57
Concentration Optimization Study for % Adsorption of lead Ions on
RHC, KMRHC, RHA and KMRHA, Adsorbent Dose = 2g/L pH = 6,
Temp = 303K, Agitation Time = 50min
170
4.58
Effect of pH‘ on Uptake Capacity of Pb
2+ on RHC, KMRHC, RHA and
KMRHA 176
4.59
Effect of pH‘ on Percent Adsorption of Pb
2+ on RHC, KMRHC, RHA
and KMRHA 176
4.60
Effect of ‗Temperature‘ on the Uptake Capacity (mg/g) of Pb
2+ on
RHC, KMRHC, RHA and KMRHA. 180
4.61
Effect of Temperature‘ on %.Adsorption of Pb
2+ on RHC, KMRHC,
RHA and KMRHA 180
4.62
Plots of Free Energy‘ Vs Temperature for the Adsorption of Pb
2+on
RHC, KMRHC, RHA and KMRHA-Adsorbents 183
4.63
Pseudo.-First Order
, Kinetics Model for‘ Adsorption of Pb
2+ on RHC,
KMRHC, RHA and KMRHA-Adsorbents 185
4.64
Pseudo.-Second Order‘ Kinetics Model for Adsorption of Pb
2+ Ions on
RHC, KMRHC, RHA and KMRHA-Adsorbents 186
4.65
Freundlich Isotherm for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA
and KMRHA from Aqueous Solution 188
4.66
Langmuir‘ Isotherms for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA,
and KMRHA from Aqueous Solution 189
4.67
Temkin Isotherms for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA
and KMRHA from Aqueous Solution 190
4.68
Comparative Study of Adsorption of Orange G Dye on RH, RHC,
RHA, KMRHC and KMRHA 192
xiv
4.69
Comparative ‗Study of the Adsorption‘ of Orange G Dye on RH, RHC,
RHA, KMRHC and KMRHA 193
xv
List of Table
Tab. No. Title
Page No.
1.1 Applications of Some of the Important Dyes.
6
1.2 Classifications of Dyes on the Basis of Their Chromophores.
7
1.3 Relationship of Wavelength to Color Absorbed/Observed
9
1.4 Toxic Effects of Heavy Metals
22
4.1 Effect of
‗Temperature
‘ on the Activation of RHC‘
71
4.2 Effect of
‗Temperature
‘ on the Activation of KMRHC‘
72
4.3 Effect of
‗Temperature
‘ on the Activation of RHA‘
72
4.4 Effect of
‗Temperature
‘ on the Activation of KMRHA‘
73
4.5
Time Optimization Study for ‗Adsorption of OG‘ on Rice Husk Char.
Co= 80 Mg/L, Initial pH = 4, Temp = 303K Adsorbent Dose = 2g/L 77
4.6
Time Optimization Study for Adsorption‘ of OG on KOH Modified Rice
Husk Char. Co= 80 mg/L, Initial Ph = 4, Temp = 303K Adsorbent Dose =
2g/L, Volume of Dye Solution = 50ml
78
4.7
Time Optimization Study for ‗Adsorption of OG
‘ on Rice Husk Ash. Co=
80 mg/L, Initial pH = 4, Temp = 303K, Adsorbent Dose = 2g/L 79
4.8
Time Optimization Study for Adsorption‘ of OG Dye on KOH Modified
Rice Husk Char. Co= 80 mg/L, Initial pH= 4, Temp = 303K Adsorbent
Dose = 2g/L.
80
4.9
Adsorbent Dose Optimization Study for Adsorption of Orange G Dye on
Rice Husk Char. Co= 80 mg/L, Initial pH = 4, Temp = 303K, Agitation
Time =80min,
84
4.10
Weight Optimization Study for the ‗Adsorption, of OG
‘ on KOH
Modified Rice Husk Char. Co= 80 mg/L, pH= 4, Temp = 303K Contact 84
xvi
Time = 60min
4.11
Adsorbent Dose Optimization Study for Adsorption of OG on RHA. Co=
80 mg/L, Initial pH = 4, Temp = 303K, Agitation Time=80min 85
4.12
Weight Optimization Study for ‗Adsorption of OG‘ on KMRHA, Co= 80
mg/L, pH = 4, Temp = 303K, Contact Time = 70mins, Volume of Dye
Solution = 50ml
85
4.13
Concentration Optimization Study for Adsorption of Orange G Dye on
Rice Husk Char. Adsorbent Dose = 2g/L, Initial pH= 4, Temp = 303K, 89
4.14
Concentration Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Char. Adsorbent Dose = 2g/L pH = 4, Temp =
303K,
90
4.15
Concentration Optimization Study for Adsorption of Orange G Dye on
Rice Husk Ash. Adsorbent Dose = 2g/L, pH. = 4, Temp. = 303K, stirring
Time. =60 min
91
4.16
Concentration Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Ash. Adsorbent Dose = 2g/L pH = 4, Temp =
303K, Contact Time = 70mins
92
4.17
pH Optimization Study for Adsorption of Orange G dye on Rice Husk
Char. Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L,
Temp = 303K, Agitation Time = 60min
96
4.18
pH Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Char. Adsorbent Dose = 2g/L C0= 80mg/L,
Temperature = 303K, Contact Time = 80min
96
4.19
pH Optimization Study for ‗Adsorption
‘ of Orange G Dye on RHA.
Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp =
303K, Agitation Time =60 min
97
4.20
pH Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Ash. Adsorbent Dose = 2g/L, C0= 80mg/L,
Temperature = 303K,Contact Time = 70min
97
4.21 Temperature Optimization Study for Adsorption of Orange G Dye on 101
xvii
Rice Husk Char. Adsorbent Dose = 2g/L,C0= 80mg/L, pH = 4 Contact
Time = 80min
4.22
Temperature Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Char. Adsorbent Dose = 2g/L, C0= 80mg/L,
pH = 4, Contact Time = 80min.
101
4.23
Temperature Optimization Study for Adsorption of Orange G Dye on
Rice Husk Ash. Adsorbent Dose = 2g/L,C0= 80mg/L, pH = 4, Contact
Time = 60min
102
4.24
Temperature Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Ash. Adsorbent Dose = 2g/L,C0= 80mg/L, pH
= 4, Contact Time = 70min
102
4.25
Thermodynamic Parameters, for Adsorption of OG dye on RHC,
KMRHC, RHA and KMRHA-adsorbents 105
4.26
The Values of Rate. Constants
.K1 and K2, qe And Their R
2for the
Adsorption‘ of OG Dye on RHC, KMRHC, RHA and KMRHA-
Adsorbents
108
4.27
Parameters in Langmuir., Freundlich
. and Temkim Adsorption Isotherm
Models for Adsorption of OG Dye on RHC,KMRHC, RHA and
KMRHA from Aqueous Media.
114
4.28
Time Optimization Study for Adsorption of TY Dye on RHC., Co= 80
Mg/L, Initial pH = 3.5, Temp = 303K,Adsorbent Dose = 2g/L 118
4.29
Time Optimization Study for the Adsorption of TY Dye on KOH
Modified Rice Husk Char. Co= 80 mg/L, Initial pH = 3.5, Temp = 303K,
Adsorbent Dose = 2g/L,
119
4.30
Time Optimization Study for Adsorption of TY Dye on RHA. Co = 80
mg/L, Initial pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L 120
4.31
Time Optimization Study for Adsorption of TY Dye on KMRHA. Co =
80 mg/L, Initial pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L 121
4.32
Adsorbent Dose Optimization Study for Adsorption of TY Dye on RHC,
Co = 80 mg/L, Initial pH = 3.5, Temp = 303K, Agitation Time =70min, 125
xviii
4.33
Weight Optimization Study for Adsorption of TY on KOH Modified
Rice Husk Char. Co = 80 mg/L, pH = 4, Temp = 303K, Contact Time =
60min
125
4.34
Adsorbent Dose Optimization Study for Adsorption of TY Dye on Rice
Husk Ash. Co= 80 mg/L, Initial pH = 3.5, Temp = 303K, Agitation Time
=70min
126
4.35
Weight Optimization Study for Adsorption of TY Dye on KOH Modified
Rice Husk Ash. Co = 80 mg/L, pH = 3.5, Temp = 303K, Contact Time =
60mins
126
4.36
Concentration Optimization Study for ‗Adsorption‘ of TY Dye on RHC,
Adsorbent Dose = 2g/L, Initial pH = 3.5, Temp = 303K, Agitation Time
=70 min
130
4.37
Concentration Optimization Study for the Adsorption of TY Dye on
KOH Modified Rice Husk Char, Adsorbent Dose = 2g/L, pH = 3.5,
Temp = 303K, Contact Time = 60min
131
4.38
Concentration Optimization Study for ‗Adsorption‘ of TY Dye on RHA,
Adsorbent Dose = 2g/L, Initial pH = 3.5, Temp = 303K, Agitation Time
=70 min
132
4.39
Concentration Optimization Study for Adsorption of TY Dye on KOH
Modified Rice Husk Ash. Adsorbent Dose = 2g/L pH = 3.5, Temp =
303K Contact Time = 60min
133
4.40
pH Optimization Study for the ‗Adsorption of TY‘ Dye on RHC,
Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp =
303K, Agitation Time =70min
137
4.41
‗pH‘ Optimization Study for the Adsorption of TY Dye on KOH
Modified Rice Husk Char. Adsorbent Dose = 2g/L, C0= 80mg/L,
Temperature = 303K,Contact Time = 80mins
138
4.42
pH Optimization Study for ‗Adsorption‘ of TY Dye on RHA, Adsorbent
Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp = 303K,
Equilibrium Agitation Time
139
xix
4.43
pH Optimization Study for the Adsorption of TY Dye on KOH Modified
Rice Husk Ash, Adsorbent Dose = 2g/L, C0= 80mg/L, Temperature =
303K,Contact Time = 80mins.
140
4.44
Temperature Optimization Study for ‗Adsorption‘ of TY Dye on RHC,
Adsorbent Dose = 2g/L,C0 = 80mg/L, pH = 3.5, Contact Time = 70 min 144
4.45
Temperature Optimization Study for the Adsorption of TY Dye on KOH
modified Rice Husk Char. Adsorbent Dose =2g/L, C0 = 80mg/L, pH =
3.5, Contact Time = 60min
144
4.46
Temperature Optimization Study for ‗Adsorption‘ of TY Dye on RHA,
Adsorbent Dose = 2g/L, C0 = 80mg/L, pH = 3.5, Contact Time = 70 min 145
4.47
Temperature Optimization Study for ‗Adsorption‘ of TY Dye on
KMRHA, Adsorbent Dose =2g/L, C0 = 80mg/L, pH = 3.5, Contact Time
= 60min
145
4.48 ‗Thermodynamic Parameters‘ for the Adsorption of TY Dye on RHC,
KMRHC, RHA and KMRHA-Adsorbents 148
4.49
The Numerical Values of Rate Constants K1 andK2, qe and their R2for
the Adsorption of TY Dye on RHC, KMRHC, RHA and KMRHA-
Adsorbents
152
4.50
Parameters in Langmuir,, Freundlich. and Temkim Adsorption Isotherms
for Adsorption of TY on RHC, KMRHC, RHA and KMRHA-adsorbents 156
4.51
Time Optimization Study for Adsorption of Lead Ions Rice Husk Char.
Co = 250 mg/L, pH = 6, Temp = 303K, Adsorbent Dose = 2g/L 160
4.52
Time Optimization Study for Adsorption of Lead Ions on KMRHC Co =
250 mg/L, pH = 6, Temp = 303K, Adsorbent Dose = 2g/L 160
4.53
Time Optimization Study for Adsorption of Pb2+
on RHA, Co = 250
mg/L, pH = 6, Temp = 303K,Adsorbent Dose = 2g/L 161
4.54
Time Optimization Study for Adsorption ofPb2+
on RHA, Co = 250
mg/L, pH = 6, Temp = 303K, Adsorbent Dose = 2g/L 162
4.55
Weight Optimization Study for, Adsorption of Pb
2+ on RHC, Co = 250
mg/L, pH = 6, Temp = 303K Agitation Time = 50min 166
xx
4.56
Weight Optimization Study for, Adsorption of on Pb
2+ on KMRHC, Co =
250 mg/L, pH = 6, Temp = 303K Agitation Time = 50min 166
4.57
Weight Optimization Study for, Adsorption of Pb
2+ on RHA, Co = 250
mg/L, pH = 6, Temp = 303K,Agitation Time = 80min 167
4.58
Weight Optimization Study for, Adsorption of Pb
2+ on KMRHA, Co =
250 mg/L, pH = 6, Temp = 303K, Agitation Time = 70min 167
4.59
Concentration Optimization Study for Adsorption of Lead Ions on Rice
Husk Char. Adsorbent Dose = 2g/L, pH = 6, Temp = 303K, Agitation
Time = 50min
171
4.60
Concentration Optimization Study for Adsorption of Lead Ions on KOH
Modified Rice Husk Char. Adsorbent Dose = 2g/L, pH = 6, Temp =
303K, Agitation Time = 50min,
172
4.61
Concentration Optimization Study for Adsorption of Pb2+
on RHA,
Adsorbent Dose = 2g/L, pH = 6, Temp = 303K, Agitation Time = 80min 173
4.62
Concentration Optimization Study for Adsorption of Lead Ions on KOH
Modified Rice Husk Ash, Adsorbent Dose = 2g/L (0.1g/50ml), pH = 6,
Temp = 303K, Agitation Time = 70min.
174
4.63
pH Optimization Study for Adsorption of Pb2+
on RHC, Adsorbent Dose
= 2g/L Co = 250 mg/L, Temp = 303K, Agitation Time = 50min 177
4.64
pH Optimization Study for Adsorption of Pb2+
on KOH Modified Rice
Husk Char. Adsorbent Dose = 2g/L, Co = 250 mg/L, Temp = 303K, 177
4.65
pH Optimization Study for Adsorption of Pb2+
onRHA.AdsorbentDose =
2g/L, Co = 250 mg/L, Temp = 303K, Agitation Time = 80min. 178
4.66
pH Optimization Study for Adsorption of Lead Ions on KOH Modified
Rice Husk Ash, Adsorbent Dose = 2g/L, Co = 250 mg/L, Temp = 303K,
Agitation Time = 70min,
178
4.67
Temperature Optimization Study for Adsorption of Pb2+
on Rice Husk
Char. Adsorbent-.Dose = 2g/L, Co = 250 mg/L, pH = 6, Agitation Time =
50min
181
4.68 Temperature Optimization Study for Adsorption of Lead Ions on KOH 181
xxi
Modified Rice Husk Char. Adsorbent Dose = 2g/L, Co = 250 mg/L, pH =
6 Agitation Time = 50min
4.69
Temperature Optimization Study for Adsorption of Pb2+
on RHA,
Adsorbent Dose = 2g/L, Co= 250 mg/L, pH = 6, Agitation Time = 80min 182
4.70
Temperature Optimization Study for Adsorption of Pb2+
on KMRHA,
Adsorbent Dose = 2g/L, Co = 250 mg/L, pH = 6, Agitation Time =
70min.
182
4.71
‗Thermodynamic Parameters‘ for Adsorption of Pb
2+ on RHC, KMRHC,
RHA and KMRHA-Adsorbents 184
4.72
The Numerical Values of ‗Rate Constants‘K1 andK2, qe and R
2for the
Adsorption of Pb2+
Ions on RHC, KMRHC, RHA and KMRHA-
Adsorbents
186
4.73
Parameters in Langmuir‘, Freundlich. and Temkim Adsorption Isotherm
Models for‘ Adsorption of Pb2+.
on RHC, KMRHC, RHA and KMRHA
from Aqueous Solution
191
xxii
List of Abbreviations
AG Acid Green
Al-SA Aluminum-Succinic Acid
AMD Acid Mine Drainage
AOX Adsorbable Organic Halides
API American Petroleum Institute
ARD Acid Rock Drainage
BG Brilliant Green
BOD Biochemical Oxygen Demand
CEC Cation Exchange Capacity
CIP Ciprofloxacin
CNT Carbon Nanotube
COD Chemical Oxygen Demand
CS Chitosan
CV Crystal Violet
DDT Dichlorodiphenyltrichloroethane
DG Direct Green
DNH Double Network Hydrogel
DSC Differential Scanning Calorimetry
EDA Ethylenediamine
EDS Energy Dispersive Spectroscopy
EDTA Ethylene Diamine Tetraacetic Acid
ENR Enrofloxacin
xxiii
FA Folic Acid
FAAS Flame Atomic Absorption Spectroscopy
FQs Fluoroquinolones
FTIR Fourier Transform Infrared
GC Gas Chromatograph
GFAAS Graphite Furnace Atomic Absorption Spectrometer
GO Graphene Oxide
GS Glass Spiral
HPLC High Performance Liquid Chromatography
KMRHA KOH Modified Rice Husk Ash
KMRHC KOH Modified Rice Husk Char
KR Kiton Red-620
LCSA Luffacylindrica Sponge Adsorbent
LDH Layered Double Hydroxides
LG Light Green
MB Methylene‘ Blue
MDW Molasses Distillery Wastewater
MG Malachite Green
MO Methyl Orange
Mp(GMA-EGDMA (Magnetic Poly(Glycidylmetharylate-Ethyleneglycoldimethacrylate)]
MS Magneticsilica
MTL Matured Tea Leaf
MWCNT Multi-Walled Carbon-Nanotubes
xxiv
NF Nano-Filtration
Ni/PC-CN Nickel Nanoparticles Embedded In Porous Carbon and Carbon Nano-
Tubes
NOR Nor-Floxacin
OG Orange Gelb
OX Organic Halides
PA Phytic Acid
PAH Polycyclic Aromatic Hydrocarbons
PAM Polyacrylamide
PAN Poly Acrylonitrile Nano fibers
PCBMC Polycarboxy betaine Methacrylate
PMMA Polymethyl methacrylate
QAC Quaternary Ammonium Compound
RB Reactive Black
RH Rice Husk
RHA Rice Husk Ash
RhB Rhodamine‘ B
RHC Rice Husk Char
RO Reverse osmosis
RR Reactive Red
SDS Sodium Dodecyl Sulfate
SEM Scanning Electron Microscopy
SMA Styrene-Alternative-Maleic Anhydride
SMCS Surfactant-Modified Chitosan
xxv
SR Sulforhodamine
SS Suspended Solids
S.S Stainless Steel
T.S.S Total Suspended‘ Solids
TDS Total Dissolved Solids
TEM Transmission electron Microscopy
TG Thermo gravimetry
TGA Thermo-Gravimetric Analysis
TOC Total Organic Carbon
TTA Tris(2-Aminoethyl)Amine
TY Titan Yellow
WCFs Aste Cotton Fibrics
XRD X-Ray Diffraction
ZIF-67 Zeoliticimidazolate Frameworks-67
xxvi
Dedicated to my Parents
xxvii
Acknowledgement
I feel great delight and happiness in expressing my gratitude to my research
supervisor Dr. Abbas Khan, for his motivating and stirring guidance, devotion of
time, valuable suggestion and courteous behavior in completing this work.
I am thankful to Prof. Dr Zahid Hussain, Chairman Department of Chemistry,
Abdul Wali Khan University Mardan, for providing all sorts of facilities, required
for the completion of this work.
I am also thankful to HED Khyber Pakhtunkhwa, for providing the NOC for
this study.
Last but not the least I wish to thank my parents and my family members for
their financial and moral support
Abdul Malik
1
ABSTRACT
Rice Husk (RH) was collected from the local rice processing mill in district Mardan,
Khyber Pakhtunkhwa, Pakistan. The RH was thermally modified in the absence of air at 400oC to
prepare the Rice Husk Char (RHC). Whereas the thermal modification of RH in the presence of air
at 700oC leads to the production of Rice Husk Ash (RHA). Both the RHC and RHA were
modified with KOH and labeled as KOH Modified Rice Husk Char (KMRHC) and KOH
Modified Rice Husk Ash (KMRHA). The thermally and Thermo-chemically modified material
were subjected as adsorbents for the removal of toxic dyes (Orange G and Titan yellow) and heavy
metal ions (Pb2+
) from aqueous media. Variation in the experimental conditions (agitation time,
dye/metal ions concentration, adsorbent dose, pH and temperature) play significant role in the
adsorption process. The maximum adsorption capacity of Orange G (OG) on RHC and KMRHC
was investigated as 28.8 mg/g and 38.4 mg/g respectively at pH = 4 using initial dye
concentrations of 80 mg/L containing 2g/L of the adsorbent dose with agitation speed of 240 rpm
at 303K. Under the same experimental conditions the uptake capacity (mg/g) of OG on RHA and
KMRHA was inspected as 23.05 mg/g and 36.45 mg/g respectively. The percentage adsorption of
OG on RHC and KMRHC were recorded as 65.1% and 96.0% respectively, whereas that on RHA
and KMRHA was noted as 57.6% and 91.1% respectively. These results indicated that KOH
modification of RHC and RHA resulted into efficient adsorbents for the removal of OG dyes from
aqueous media. Almost similar results were also investigated for the removal of Titan yellow (TY)
dye on these adsorbents. Slight variation the adsorption capacities (mg/g) and percent adsorption
was attributed to the structural and compositional changes in the OG and TY dyes. The maximum
removal of TY on these adsorbents were investigated at pH = 3.5.
The optimum adsorption capacities (mg/g) of Pb2+
ions on RHC, KMRHC, RHA and
KMRHA-adsorbents were investigated as 92.2mg/g, 119mg/g, 86.75mg/g and 113.7 mg/g
respectively. This suggested that the modification of RHC with KOH enhanced its adsorption
capacity from 92.2 to 119mg/g while that of RHA from 86.75 and 113.7 mg/L. The metal ions
adsorption experiments were performed using initial Pb2+
ions concentrations of 250 mg/L
containing 2g/L of the adsorbent dose at pH = 6 with stirring speed of 240 rpm at 303K. The
maximum adsorption efficiencies of Pb2+
ions were noted as 74%, 95.9%, 86.75% and 90.6% on
RHC, KMRHC, RHA and KMRHA-adsorbents respectively. This revealed that the percent
2
adsorption of Pb2+
ions on KMRHC and KMRHA are greater than the corresponding values of
RHC and RHA, which suggested that KOH modified Rice Husk Char and Rice Hush Ash
(KMRHC and KMRHA) are efficient adsorbents for the removal of Pb2+
ions from aqueous
media. Adsorbent dose have a significant role on the adsorption capacity of metal ions on
adsorbents. For 1g/L of adsorbent dose, the maximum adsorption capacity for Pb2+
ions on RHC,
KMRHC, RHA and KMRHA was inspected as 136mg/g, 172mg/g, 106mg/g and 152 mg/g
respectively other experimental conditions were the same as mentioned above.
Thermodynamic studies of the adsorption of OG, TY and Pb2+
on RHC, KMRHC, RHA
and KMRHA indicated that the values of ΔG and ΔH were negative which revealed that the
adsorption process is exothermic and spontaneous. The negative value of ΔS suggested that
randomness decreases at the interface of adsorbent-adsorbate during the adsorption process. The
kinetics study indicated that the experimental data of the adsorption process best fits to pseudo-
second order kinetic model. The equilibrium data was tested on Langmuir, Freundlich and Temkin
adsorption isotherm models. It was inspected that the data followed all the three isotherm models
(R2>0.90). However, the values of correlation coefficients (R
2) indicated that the data is mostly
best fit to the Langmuir isotherm model (R2>0.98) which suggest for chemi-sorption process. The
RHC, RHA and KOH modified RHC and RHA were characterized by XRD, SEM, FTIR and
EDX. XRD pattern indicated the crystalline entities in the amorphous matrix had blocked the
aggregation of silica particles and hence enhanced the surface area of the adsorbents for the
maximum adsorption of dyes and heavy metal ions. SEM images indicated that the KOH
modification of RHC and RHA made these materials highly porous which enable them more
efficient adsorbents for the adsorption of toxic dyes and heavy metals from aqueous media.
In the light of experimental results so obtained it was found that within the experimental
range of various parameters used, the adsorption rate is appreciably affected but the overall order
and hence the mechanism of adsorption may remain the same. However, the nature and
mechanism of adsorption may vary by changing the type/nature of different adsorbents prepared.
The overall results obtained in this work suggested that our new material would be applied for the
removal of toxic dyes and heavy metals from waste water as an alternate and easier option. It will
also motivate further research in the direction of removal of contaminants by applying modified
RH.
1
INTRODUCTION CHAPTER#1
Dyes and heavy metals are the toxic and harmful pollutants of the aquatic environment. Their
removal is very necessary from aqueous media. Treatment of the waste water of food, paper,
textile and dyeing industries before discharging to aquatic environment is a challenge to be
competed (Zakaria, et al., 2009; Aksu, 2005). The toxic effluents of different industries affect
adversely the water resources, aquatic organisms, soil fertility and biological ecosystem. Colored
effluents from the textile industries is one of the challengeable problems. Application of colors
enhances the appearance of almost all materials. The application of the natural colorants
extracted from vegetables, fruits, flowers, insects and fish, has been found since 3500 BC. Color
gives attraction to fabrics and other industrial products. The industrial products lose their
commercial value if not suitably colored. Fabrics were earlier being colored with natural dyes.
The natural dyes however provided a limited range of colors. Besides, they have low color
fastness on the exposure to sunlight and washing. Consequently, they required a mordant to
make a dye complex in order to fix dye to the fiber which was a tedious work for the years. The
synthetic dyes (discovered by Perkins, 1856) have a very broad range of colorants which are
color-fast and have brighter shades (Kant, 2012). As a result the application of dyes increased to
its extreme today. The natural dyes were utilized as colorants for textile products up to 19th
century. The synthetic dyes are toxic and allergic which made the use of natural dyes as an
essential demand for the textile products (Anitha & Prasad 2007). Approximately 150 years ago
almost all of dyes were the derivative of natural source like flora and animals which were mainly
consist of pigments (Kumaresan, et al., 2012).
The main source of industrial wastewater is textile industry. The waste water from textile
industries is polluting the aquatic environment to the highest degree as compare to the other
industries (Aksu, et al., 2005). Varieties of chemicals are used in textile processing like
bleaching, dyeing and finishing. The textile industries utilize high quantity of water for different
purposes. The discharged waste-water of textile industries is mostly colored due to dyeing
processing of the textile products which cause toxicity and disturbing the aquatic environment
(Mishra, et al., 2010). Dyes are mostly aromatic organic compounds that could be used to color
various materials like textile fiber, paper, plastic material, leather, cosmetics, and foodstuff
(Karthik, et al., 2014; Kamil, et al., 2014). Textile dyes are anionic, cationic and aromatic
2
compounds. About 100,000 commercial dyes and more than 700‘000 tons of dyes are
manufactured yearly. Approximately 10% of total textile dyes are discharged to the aquatic
environment (Gupta, et al., 2005).
1.1 Classification of Dyes
Dyes are colored substances that have affinities for the fabric materials. The dyes are
usually used in the solutions made in water; mordents are required to improve the fastness of
dyes on fabric materials. Dyes and pigments are colored materials, due to the absorbance of
wavelengths in the visible region. Dyes are mostly water soluble. However, some dyes are not
soluble in water. Solubility and chemical properties are the two major factors which could
classify the dyes (Booth, et al., 2000).
1.2 Classification Based on Origin
Origin based classification divided the dyes into three groups (Bhattacharyya, 2010;
Samanta, 2011).
1.2.1 Plant-Origin
Dyes are mostly originated from the various parts of the plants like seeds, flowers, leaves,
trunks, barks, and roots, etc. In India, approximately 450 plants are dye yielding.
1.2.2 Animal-Origin
Red animal dye is derived from the dried bodies of insects like, Kermes, Cochineal,
Kerria, Laccifer and Mollusc like kermesic acid (Kermes), carminic acid Tyrian purple etc.
1.2.3 Mineral-Origin
Different types of pigments belong to metal-salts and metal-oxides are termed as mineral-
origin dyes. Colorants belongs to mineral-origin are further classified according to their colors.
3
1.2.3.1 Red-Pigments
Cinnabars, Red-lead, Red Ochre and Realgars are the common red-pigments, belonging
to mineral origin. Cinnabar refers to brick-red form of HgS. Red lead (Pb3O4) is a red pigment
which may be crystalline or amorphous. Red Ochre is containing anhydrous and hydrated iron
oxide (Fe2O3·nH2O). The color of Red Ochre ranges from yellow to brown. Realgars (α-As4S4)
are arsenic-sulphides minerals which arealso called as Ruby-sulphur.
1.2.3.2 Yellow-Pigments
Yellow-Ochre, Orpiment, Raw-Sienna, and Litharge are grouped into yellow-pigments.
The color of Yellow Ochre is due toFe2O3·H2O. Orpiment is orange-yellow arsenic-sulphide
(As2S3). Raw Sienna is an earth pigment which consists of iron oxide & manganese oxide.
Litharge (Massicot) is a secondary form of lead oxide (PbO).
1.2.3.3 Green Pigments
Terre-Verte, Vedgiris and Malachite are the commonly known green pigments. Terre-
Verte is a generally used-pigment. It is a combination of hydro-silicates of Al, Mg, Fe, and K.
Malachite is Cu2(OH)2CO3 (copper carbonate hydroxide).
1.2.3.4 Blue-Pigments
Ultra-marine Blue & Azurites are the examples of blue-pigments. Ultramarine blue is a
deep-blue colored pigment which is obtained from lapis lazuli (a semi-precious stone). Azurites
are prepared by weathering of the copper-ore de-posits. These pigments were widely employed
in Chinese-paintings.
1.2.3.5 White Pigments
Chalks, White Lead & Zinc White are the examples of white pigments. Chalk is the form
of calcium carbonate (CaCO3). It has been widely employed in paintings. White Lead (PbCO3)
consists of both carbonate & hydroxide. It is an ingredient of lead paint. Zinc White (ZnO) is an
important pigment and is widely used in painting.
4
1.2.3.6 Black-Pigments
Charcoal-Black, Lamp-Black, Bone-Black, Ivory Black, Black-Chalk Graphite, and Terre
Noire are the most common examples of black-pigments. Sound grounded char-coal is mostly
applied as black pigments. Kajal, a black pigment which is prepared from the burning of oil in a
lamp, the soot is deposited on the earthen bowl. Ivory-Black was manufactured from the charring
of ivory-cuttings in a closed earthen-pot. Bone-Black is produced by charring animal bones in
closed earthen- pot. Powdered Graphite is used for writing purposes. It is a dull grey-pigment.
Black-Chalk is the black-clay which is employed for painting. Terre-Noire is a combination of
carbonates of iron, manganese and calcium.
1.3 Classification Based on Application Methods
1.3.1 Organic Dyes
Most of the dyes are organic in nature. The organic dyes are mostly derived from plants;
however some of them are synthetic organic dyes. They are employed in lasers, optical-media,
and camera-sensors (Burgess, 2011).
1.3.2 Acid Dyes
These dyes are mostly water soluble and anionic in nature. They can be applied to silk,
nylon, wool and other fibers like modified acrylic fibers in neutral or acidic media. The attractive
force among the an-ions and cat-ions of the fiber attribute to the attachment of dye to the fiber.
These dyes are not important to cellulose. Food dyes are mostly acid dyes. Examples of these
dyes are Pure Blue B, Alizarine Acid Red 88 etc. (Hunger, 2007).
1.3.3 Basic-Dyes
These are cationic dyes which are soluble in water. They are used mostly to acrylic-fibers
and silks. Addition of acetic acid enhances the adhesive forces of dyes to the fibers. They are
used to color the papers (Brachet, 1953).
5
1.3.4 Direct Dyes
These are also known as substantive dyes. They can be applied mostly in neutral or
slightly alkaline media at boiling temperature. NaCl (Sodium Chloride) or Na2SO4 (Sodium
Sulfate) or Na2CO3 (Sodium Carbonate) can be mixed with the dye. Direct dyes are also used
for dyeing the cotton, wools, leather, silks, papers and nylon (Waring, & Hallas, 2013).
1.3.5 Mordant-Dyes
They need mordent to improve their fastness against moisture, perspiration and light.
Specific mordant is needed for different dyes because mordant can change the color of the dye
significantly. The natural dyes are mostly mordant dyes for which various dyeing techniques are
described in the literature. The synthetic mordant dyes are very important dyes that can be
applied to wool. 30% of these dyes are applied to wool, and black/navy shades. The mordant
dyes containing heavy metals are mostly hazardous to health. These dyes can be used carefully
(Waring & Hallas, 2013).
1.3.6 Vat-Dyes
They are not soluble in water. They may be reduced in alkaline liquor so that to prepare
their water-soluble alkali metal salts, which has an attraction for the fibers. Subsequent oxidation
can be used to return the dyes into original insoluble dyes. The indigo impart color to denim, is
the example of original vat dye (Zollinger, 2003).
1.3.7 Azoic Dyeing
It is a technique which is used to prepare as insoluble azo dye for direct attachment to the
fiber. The fiber is treated with diazoic and couple components adjusted with appropriate
conditions of dye tub for the reaction of the two components to prepare the necessary water
insoluble azoic dye. This is a unique dyeing technique; the final color can be controlled by
controlling the diazoic and coupling components. In this technique toxic chemicals are used
which made its efficiency declined (Booth, et al., 2000). In mammals, the bacterial and hepatic
azoreductases convert the azo amines (Bragger, et al., 1997). The activity of Bacteria-
6
azoreductases is higher than hepatic-azoreductases hence producing carcinogenic and mutagenic
amines during the reduction of azo dyes to the corresponding amines. Benzidine is used in textile
dyeing, paper and leather printing industries. BZ-based azo dyes cause cancer and tumor in the
bladder of laboratory (experimental) animals (Haley, et al., 1975).
1.3.8 Specific Applications of Dyes
Some of the important dyes and their specific applications are given as in table
1.1(Booth, et al., 2000).
Table 1.1 Applications of Some of the Important Dyes.
Dyes Applications
Oxidation bases Hair and fur
Leather-dye Leather
Fluorescent-brightener Fibers, papers
Solvent-dyes Wood-staining, Colored-lacquers, Solvent-
inks etc.
Contrast-dyes Injected for MRI(magnetic resonance
imaging), clothing
Mayhems dye Water cooling for looks, rebranded RIT dye
1.4 Classification Based on Chromophores
The dye-taxonomy on the basis of their respective chromophores is given in the
following table (Stolarska & Garbalińska, 2017).
7
Table1.2 Classifications of Dyes on the Basis of Their Chromophores.
Chromophor based Dyes Chromophores.
Acridine dyes Acridine.
Anthraquinone dyes Anthraquinone.
Diarylmethane dyes Diphenyl methane.
Triarylmethane dyes Triphenylmethane.
Azo dyes -N=N-.
Diazonium-dyes Diazonium–salts.
Nitro-dyes -NO2.
Nitroso-dyes -N=O.
Phthalocyanine dyes Phthalo-cyanine.
Quinone-imine dyes Quinone.
Safranin dyes Safranin.
Indophenol dyes Indophenols.
Oxazin-dyes Oxazin.
Oxazone-dyes Oxazone.
Thiazine-dyes Thiazine.
Thiazole-dyes Thiazole.
Safrani- dyes Safranin.
Xanthene-dyes Xanthene.
Fluorene-dyes Fluorene.
Fluorone-dyes Fluorone.
Rhodamine-dyes Rhodamine.
1.5 Major Groups
Almost all types of dyes are classified into two major groups, the natural and synthetic
dyes.
8
1.5.1 Natural Dyes
Most of the natural dyes are extracted from various parts of the plants: roots, leaves,
berries, bark, fungi, lichens and wood. At the very beginning, the people used the locally
available materials to dye their textiles. Brilliant and permanent dyes were found rarely. These
dyes included tyrian purple, invertebrate dyes, crimson kermes, saffron, woad, indigo and
madder. These dyes were important as trade goods and hence contributed to the economies. India
and Phoenicia carried out the dyeing for over 5,000 years as indicated by the archaeological
evidences. These dyes were mostly obtained from animal, plant, and mineral sources. Plant
kingdom was considered as the largest source of dyes. However, very small quantity of these
dyes was used commercially.
1.5.2 Synthetic-Dyes
They are generally manufactured from petroleum. The first synthetic dye was mauveine
(organic aniline dye) which was exposed by W.H. Perkin in 1856. After this discovery,
thousands of dyes were manufactured (Kvavadze, et al., 2009).
1.6 Effect of Dyeing Industrial Waste Matter on Vegetation
The fertility of farming lands can be severely affected, if irrigated with water polluted
with different industrial waste matter. The bio-chemical composition of the earth and water can
be changed by industrial effluents which adversely affect the development and output of
vegetation. All of the biologically active compounds in waste are difficult to analyze. Dyeing
factories effluents, not only alter the color and quality of water, but also hazardous for the
aquatic organisms (Khan & Jain, 1995). Dyeing industrial effluents can affect the plant-growth
parameters like seedling survival, germination percentage, seedling height and the rate of
germination (Nirmalarani & Janardhanan, 1988). A high concentration of industrial-effluents
inhibits the growth of shoot and root of seedlings. High concentrations of solid contaminants in
the effluents reduce the degree of dissolved oxygen, which restrict the growth and development
of plants (Saxena, et al., 1986). Chlorophylls of plants are decreased due to industrial effluents or
high concentrations of dissolved solids wastes.
9
1.7 Chemistry of Dyes
1.7.1 Basis for Color
Dyes are colored compounds since
They take up electro-magnetic radiations in the visible region
They have chromophores
They contain conjugated systems and show electronic resonance (Abrahart, 1977).
All of these features are essential for the colors of dyes, missing of any one feature could
lead to color loss of the compound. Dye compounds have auxochromes along with chromopores
which are not responsible for color however they help the chromophores. Carboxylic, amino,
sulfonic, and hydroxyl‘ groups are the examples of auxochromes. Auxochromes are mostly used
to control the solubility of dyes. Light-wavelength is related to Color Absorbed or Observed
according to table 1.3.
Table 1.3 Relationship of Wavelength to Color Absorbed/Observed
Wavelength.-Asborbed (nm.) Colour
.-Absorbed Colour
.-Observed
300-435. ‗Violet‘ ‗Yellow-Green‘
435-480. ‗Blue‘ ‗Yellow‘
480-490. ‗Green-Blue‘ ‗Orange‘
490-500. ‗Blue –Green‘ ‗Red‘
500-560. ‗Green‘ ‗Purple‘
560-580. ‗Yellow-Green‘ ‗Violet‘
580-595. ‗Yellow‘ ‗Blue‘
595-605. ‗Orange‘ ‗Green-Blue‘
605-700. ‗Red‘ ‗Blue –Green‘
The chromophore, which is responsible for color generation must be part of a conjugated
system. This can be inspected in the figure 1.1
10
Figure 1.1 Significance of Chromophore in a Conjugated-System
Figure 1.2 reveals for the significance of a widespread conjugated-system. If the length of
conjugated-system is doubled, a significant bathochromic shift is observed as in Vitamin A to
provide β-carotene which causes dark coloration.
Figure 1.2 Conjugated-Systems Present in Vitamin A and β-Carotene.
1.7.2 Dyes Versus Pigments
Keeping in mind the solubility, the organic colorants can be divided in two groups‘ i.e
dye and pigments (Allen, 1971). Dyes can be soluble in aqueous media and in organic solvents,
whereas pigments are insoluble in both types of liquid media. Dyes color those substrates for
which they have affinity while Pigments color any polymeric substrate but the mechanisms of
these are quite different from each other. The pigments are first mixed with the polymer and then
used to color the surface of fiber.
1.7.3 Dye-Substrate Affinity
Dyes, which contain at least one azo group (azo-dyes) are the major family of organic-
dyes. They may be:
Acidic dyes, which have affinity for polyamide/protein substrates like wool, nylon,
silk etc.
11
Disperse-dyes have attraction for hydro-phobic substrate like polyester, acetate etc.
Direct/reactive dyes have affinity for cellulose like cotton, linen, rayon, paper etc.
1.7.4 Dyes, Used for Polyamides/Proteins
Such dyes have ionic interaction with the substrate as indicated in the figure 1.3. Here
dyes carry negative charge (anionic dyes) and the substrates carry positive charge (cat-ionic in
nature). An-ionic dyes which are used for polyamides/proteins are called acidic dyes e.g. C.I.
acid black-1 as indicated in figure 1.4. They are called acidic dyes because they are suitable to
substrates in acidic medium.
Figure 1.3 Ionic Interaction of Dye with the Substrate
Figure 1.4 Structures of a Commercial Acid and Cationic (Basic) Dye
1.7.5 Dyes, Used for Cationic-Polymer
They also have ionic interaction with the substrate. Here, the dyes are cat-ionic in nature
that carry positive charge and the substrate are negatively charged (an-ionic in nature). They are
also called basic dyes e.g. C. I. basic red-18 as indicated in the Figure 5.
1.7.6 Dyes, Used for Cellulosic-Polymer
Here the substrate is hydrophilic which needs hydrophilic dye for dyeing. The dyes are
mostly designed to maintain affinity for their substrate. Thus the color is remained on the
substrate, even on the exposure to water. Dyes, which are used for cellulosic-polymers are azoic,
reactive, sulfur, vat, and direct dyes.
12
1.7.7 Toxicological Considerations
Environmental protection is a necessary concern in molecular plan. Therefore, raw
materials that were used for preparation of artificial dyes must have none of such compounds
which contribute to health risks. Such groups are mostly aromatic-amines (Bide, 2014) which are
carcinogenic or mutagenic (Maron and Ames, 1983). For example, dye-1 in figure 1.5 produce
the bladder carcinogen, ‗benzidine‘ if it was inter into the body.
Figure 1.5 ‗Reductive-Cleavage of Direct-Red-28 (1), Using Azo-Reductase Enzyme
1.8 Waste Water
Wastewater is the water which is affected by the use of humans. Wastewater is the used
water of home, industrial, farming activities, squall water and any drainaccess (Telly, et al.,
2014). The properties of wastewater depend on the source. Every source has different pollutants
in its wastewater. Types of waste water include: domestic wastewater, municipal wastewater,
(sewage) and industrial wastewater. Water from these sources contains different types of
biological, physical, and chemical pollutants. Households may provide wastewater from toilets,
sinks, washing machines, bath tubs, dishwashers, and showers.
13
1.8.1 Acid Mine Drainage (AMD)
The acidic discharge from active mines is known as AMD (Acid Mine Drainage). The
ARD (Acid Rock Drainage) could also be originated from these sources (Zawierucha, et al.,
2016). Both the AMD and ARD have low pH originated by the oxidation of sulfides (Ferguson
& Morin, 1991). If drainage from mines are neutral and have metals and metalloids, such
drainages were initially acidic which became neutral in their current of flow, such drainage were
called as neutral mine drainage or ‗Mining-Influenced Water‘ (Gusek, et al., 2006).
1.8.2 Complex Organic Chemicals Industry
Most of the industries manufacture or use large amount of complex organic chemicals
such as pesticides, paints, dyes, petrochemicals, pharmaceuticals, detergents, paper pollution,
and plastics, etc. Water is contaminated by feedstock materials, product materials by-products,
cleaning agents, and solvents. Treatment facilities which do not require control of their effluents
i.e. aerated lagoons (Kashiwaya, & Yoshimoto, 1980).
1.8.3 Electric Power Plants
Fossil fuel power stations, (e.g. coal-fired plants) are the major sources of industrial
wastewater. Most of these plants discharge their wastewater with significant level of metals like
lead, cadmium, mercury, arsenic, selenium, chromium and nitrogen compounds. Wastewater
stream includes flue-gas desulfurization, bottom ash, fly ash and flue gas mercury control. Plants
like wet scrubbers transfer the captured air pollutants into wastewater stream (Washington, 2004)
1.8.4 Food Industries
Wastewater produced from food and agricultural operations has specific properties. Food
processing from unrefined material needs huge mass of water. Wash of vegetables generate
water containing very large amount of particles and suspended organic matter. This water also
contains surfactants. Animals slaughter and processing generate large amount of organic waste
from body fluids, like bloods, and guts contents. These wastewaters are frequently contaminated
by high levels of antibiotics, pesticides (used to control external parasites), and growth hormones
14
from animals. The plant organic material contains salts, coloring materials, flavorings, and acids
or alkali. High quantities of oil or fats are also present. Most of the contaminants of the
agricultural and food industries are not toxic, However the high concentrations of
BOD(Biochemical Oxygen Demand) and SS(Suspended Solids) made these wastewater more
toxic (Eriksson, et al., 2007).
1.8.5 Iron/Steel ‗Industry
‘
In the preparation of iron, various reactions take place in the blast furnaces for which
water are used as coolant, which are polluted with ammonia and cyanides. Formation of coke in
coking plants also needs water as coolant. Hence water is also used for the by-products
separation. The conversion of iron into sheets, rods wires requires hot and cold transformation
stages which need lubricants and coolants and hence water is frequently employed as coolant.
Contaminants include tallow, hydraulic oils, and particulate solid matter. Iron and steel surface is
treated with strong mineral acid like sulfuric acid and hydrochloric acid to get rid of the rust and
get ready it for tin/chromium plating. Wastewaters include high quantity of ferrous chloride,
ferrous sulfate and hydraulic oil etc. The organic contaminants present in the waste streams are
gasification products like benzene, anthracene, naphthalene, cyanide, phenols, ammonia, cresols
and other organic compounds which are collectively known as PAH (Mehan, et al., 2002).
1.8.6 Pulp/Paper Industries
Effluents from pulp/paper industries are generally high in SS (suspended solids) and
BOD (Biochemical oxygen Demand). Plants which bleach wood pulp for paper manufacturing
may produce phenols chloroform, furans, dioxins (including 2,3,7,8-TCDD) and COD (chemical
oxygen demand) (Pokhrel & Viraraghavan, 2004).
15
1.8.7 Industrial Oil Contamination
Oil enters into the wastewater stream from many applications which may include
workshops, vehicle wash bays, transport hubs, fuel storage depots and power generation. Most of
the wastewaters are discharged into local streams. Typical contaminants may include detergents,
solvents, lubricants, grit, and hydrocarbons.
1.8.8 Black-Water
Black-water is generally the wastewater coming from toilets, which contains pathogens,
urine water, feces, and toilet papers. Black waters are different from of grey-water, which comes
from other domestic uses. Grey-water comes from washing food, dishes, clothing, and showering
or bathing. Black-waters are the mixture of flush water, feces, urine, and anal cleansing water.
These contain pathogens of feces and nutrients of urine (Tilley et al., 2014).
1.8.9 Determination of Adsorbable Organic Halides (AOX)
Persistent organic pollutants like DDT (dichlorodiphenyltrichloroethane), dioxins,
polychlorinated bi-phenols, are all determined in AOX analysis. Generally, high amount of
chlorine present in organic compounds, attribute to more toxicity. In a laboratory, the AOX
determination consists of the adsorption of OX (organic halides) from the samples on activated
carbon. The activated carbon in the form of powder or granular is used in micro columns
(Bornhardt, et al., 1997). Batch method may also be applied in which shaking is employed to
enhance the adsorption of OX on activated carbon. The adsorbed inorganic halides are washed
away by using strong acid like nitric acid. Quantification of AOX level can also be made by
using other analytical techniques like HPLC (high performance liquid chromatography), GC (gas
chromatography) and electron capture (Bornhardt, et al., 1997).
1.8.10 Biochemical Oxygen Demand (BOD)
BOD is a demand of dissolved oxygen which is needed for the decomposition the organic
matter present in water at a given temperature for a definite time. BOD determines the degree of
organic pollutants (Sawyer et al., 2003).Most of the pristine rivers have BOD value below than
16
1mg/L. whereas 2 to 8mg/L for reasonably polluted river. Severely polluted rivers have BOD
values greater than 8mg/L.
1.8.11 Total Dissolved Solids (TDS)
The upper limit of TDS for consumable (drinking) water is 500mg/L. Most of the aquatic
ecosystems can tolerate the maximum TDS level = 1000mg/L (Boyd 1999). Spawning fishes and
juveniles are more sensitive to very high level of TDS e.g. concentrations above 350mg/L
decreased the spawning of Moronssaxatilis whereas the concentration of TDS < 200mg/L
increased healthier spawning. TDS results into toxicity in the presence of abnormal pH, reduced
dissolved oxygen, and high turbidity etc. (Hogan, et al., 1973).
1.8.12 Total Suspended‟ Solids (T.S.S)
The T.S.S is the dry mass of all trapped particles in filter during filtration. Pre-weighed
filter having definite pore size are used to measure the T.S.S in water. The weight gained by the
filter when dried after the filtration is termed as T.S.S. Filters for T.S.S measurement are made
from glass fiber (Michaud, 1994).
1.9 Waste Water Treatment Options
The industrial waste water could be treated by chemical, physical and biological method.
However, none of these methods is as much effective as adsorption (Elsagha, et al., 2013).
Adsorption is one of the efficient methods, which is used for the treatment of industrial waste
water (Joshi, et al., 2004).
1.9.1 Activated Sludge
The areas, where the availability of earth is high, sewage is processes in big ditches give
airing (Beychok, 1967). They are also known as aeration ditches,
17
1.9.2 API Oil–Water Separator
A standard device designed by API (American Petroleum Institute) known as API oil-
water separator, is used to separate of oil from suspended-solids in the waste-water effluents at
chemical plants, petrochemical plants and other industrial sources of oily water (Beychok, 1967).
1.9.3 Ozonation
This technique is used in Europe, US and Canada. This is a cost effective method which
involves bubbling of ozone through wastewater, which break down all of the bacteria, parasites,
and other harmful organisms. However, the residual ozone and contamination of water is not
controlled after the completion of the process (Neumann, 1981).
1.9.4 Chloramination
Chloramination is becoming a common technique. The undesirable by-products produced
by chloramine are less than that produced by chlorine. The half-life of Chloramine is longer
which enable it to maintain an effective protection towards the pathogens. Chloramine has lower
redox potential than free chlorine hence it persists in distribution. It is formed by the addition of
ammonia and chlorine to drinking water. It has a very high disinfecting effect towards pathogens
(Baker, et al., 2002).
1.9.5 Chlorination, Bromination and Iodinization
Chlorine, bromine and iodine all are disinfectant against pathogens. However, chlorine is
three times more effective than bromine, and almost six times more effective than iodine (Koski,
et al., 1966).
1.9.6 Home Filtration
Water can be treated by filtration or home filtration which needs no further disinfection.
A high quantity of pathogens is removed by the materials used in the filter. The home filters can
remove about 90% of the chlorine from water. These filters should be replaced periodically
18
otherwise; the amount of bacteria to the water will increase because of their growth in the filter
unit (Newman, 1890).
1.9.7 Clarifier
Clarifier is a settling tank which is built by mechanical means for the removal of solids
by sedimentation. Sedimentation tanks were used for wastewater treatment for millennia
(Chatzakis, 2006).Primary waste-water treatment includes the elimination of settle-able/floating
solids by means of sedimentation. Primary clarifiers can reduce the proportion of TSS and
pollutants present in these solids (Mehan, et al., 2002), while the secondary clarifiers are used to
remove flocks of biological growth produced some other methods which include activated sludge
and trickling filters
1.9.8 Facultative lagoon
The facultative lagoon is almost similar in function to primary clarifier. However in this
lagoon heavy solids can settle in bottom of lagoon whereas the lighter ones are floating. The
facultative lagoon has no capability of sludge removal like primary clarifier, so anaerobic-
organisms can be accumulated at the bed of lagoon (Frostick, et al., 2014).
1.9.9 Molecular Encapsulation
Molecular encapsulation is an advanced technology, used to remove lead and other metal
ions from wastewater. Nano, micro or milli capsules, are the particles which have an active site
surrounded by carrier. The capsules under investigation are: alginate based capsules, carbon
nano-tubes and polymer swelling-capsules. These capsules are used for the best possible
treatment of waste-water.
1.9.10 Membrane Bioreactor (MBR)
MBR is a technology in which a membrane process such as microfiltration and ultra
filtration work in combination with biological treatment process like the activated sludge
process. This technology is now widely employed for industrial and municipal wastewater
treatment (Judd, 2006).
19
1.9.11 Reverse Osmosis
Reverse osmosis (RO) is technology, used for the purification of waste-water. In this
process semi-permeable membrane is used to remove large particles, ions and molecules from
drinking water. RO is used to remove suspended and dissolved particles from water it is also
used to remove bacteria from drinking water. In RO, stress is used to defeat the osmotic-pressure
as a result; solute particles are retained in pressurized side and solvent pass to the other side of
the semi-membrane (Warsinger, 2016).
1.9.12 Sedimentation
It is a physical process of waste-water treatment. In this process, the suspended-solids are
separated from water using gravity (Omelia, 1998). Solid matters are treated with the moving
water which can be removed by sedimentation. Settling basins are constructed to remove the
entrained solids through sedimentation (Goldman, et al., 1986). Clarifiers are employed for the
mechanical removal of solids by sedimentation. Sedimentation is used to treat wastewater for
millennia (Chatzakis, et al., 2006).
1.10 Heavy Metals
There are different criterions for the definition of heavy metals. For example, in
metallurgy, the criteria are based on density (Morris, 1992) in physics, it might be due to the
atomic number (Gorbachev, et al., 1980) and a chemist is mostly concerned with the chemical
behavior (Hawkes, 1997). Heavy metals have density in the range of 3.5-7gcm-3
(Duffus, 2002).
Elements fall in range of heavy metals which have atomic weight greater than Na, Ca or Hg
(Duffus, 2002). The US Pharmacopeia provided a test for heavy metals which indicated that
metallic impurities are precipitated as colored sulfides. In biochemistry, the heavy metals ions
are defined on the basis of electron pair acceptors in the aqueous solution (Rainbow, 1991).
20
1.10.1 Toxic Heavy Metals
Toxic heavy metals or metalloids are relatively dense which are noted for their potential
toxicity (Srivastava & Goyal, 2010). The term ‗toxic heavy metals‘ is particular applied for
cadmium, lead, mercury, and arsenic (Brathwaite & Rabone, 1985).
1.10.2 History of Toxic Heavy Metals
The toxicity of lead, arsenic, and mercury were recognized to the ancients. However the
toxicity of heavy metals was investigated by using proper methods from 1868. The relationship
between toxicity of heavy metals and their atomic weight were studied (Blake, 1884). A short
historical description of the toxicity of heavy metals is provided in the following section.
1.10.3 Arsenic (As)
As, as As4S4, As2S3, was recognized from primeval. Strabo, (a Greek geographer &
historian) has studied that the workers in the mine of real gar and orpiment, died due the toxic
effects of these ores (Dueck, 2000). In Asia, ground water which is contaminated by arsenic was
poisoning millions of people.
1.10.4 Mercury
The very first ruler of China was died by eating Hg pills (Zhao, et al., 2006). During the
building of Saint Isaac's Cathedral, sixty employees died due to the ornamentation of arena
(Emsley, 2011).Outbreak of Methyl-Mercury poison was happened in Japan in 1950 because of
the discharge of Hg from industries into river. The greatest identified example was in Minamata;
Here approximately six hundreds citizens died because of Minamata-disease. Twenty two
expectant women had addicted the impure fish. They exhibit no symptom of the disease but their
infants were severely disabled (Davidson, et al., 2004).
1.10.5 Lead
The toxicity of lead was recognized to the ancients. In the second century BC colic and
paralysis were described in the lead-poisoned people by Nicander (Pearce, 2007).Julius Caesar's
21
described that white lead is generated in the water pipes of lead which is harmful for humans
(Prioreschi, 1998). During 17th and 18th centuries, Devon colic condition was discovered in the
people of Devon because of drinking Pb affected cider during 2013. WHO investigated that lead
poisoning caused 143000 deaths, and 600000 scholars‘ disabilities (Organization, 2013).During
2015 the Pb level in the drinking water of Tasmania, Australia, was reached over 50 time‘s
national drinking-water guideline. The lead-jointed pipelines were investigated as the main
sources of water contamination.
1.10.6 Chromium
Potassium chromate is carcinogenic in nature. Chromium (VI) is considered as
carcinogenic since 19th century (Barceloux, 1999). In 1890, Newman investigated the elevated
carcinogenic effect in workers of chromate dye corporation (Newman, 1890). Chromate-
dermatitis was investigated within the employees of aircraft at world war-II. In 1963, the workers
of automobile factory in England suffered from dermatitis. The worker used chromate-based
paint to the Car bodies (Pollutants, 1974).
1.10.7 Cadmium
During 1910, in Japan, cadmium was discharged into the river. Rice was grown in
cadmium contaminated irrigation water which was consumed by the residents of that area. As a
result they experienced kidney failure and boon softening. The origin of the disease was not
clear. It was assumed that the disease might be due to bacterial infection or lead poisoning
(Vallero, 2013). In 1955, the cause was recognized to be related with cadmium.
1.10.8 Toxic Effects of Heavy Metals
Heavy metals can bind with nucleic acids, structural proteins, and enzymes, and affect
their functions. The toxic effects produced due to heavy metals in humans are presented in the
following table (Nielen & Marvin, 2008).
22
Table 1.4 Toxic Effects of Heavy Metals
Elements Acute Contact
(<day)
Stable Contact
(>year)
Cd 1. lung‘s inflammation
(Pneumonitis)
1. ‘Lung‘s cancer
2. ‗Osteomalacia‘
3. ‗Proteinuria‘
Hg
1. Diarrhea,
2. Fever,
3. Vomiting,
1. ‗Stomatitis‘
2. ‘Nausea’
3. ‗Nephrotic syndrome‘
4. ‗Neurasthenia‘
5. ‘Parageusia‘
6. ‘Pink Disease‘
7. ‘Tremor’
Pb
1. ‘Encephalopathy‘
2. ‗Nausea‘
3. ‗Vomiting‘
4. ‘Gastrointestinal‘
hemorrhage (bleeding)
1. ‘Anemia’
2. ‗Encephalopathy‘
3. ‘Foot drop/wrist drop’
4. ‗Nephropathy‘
Cr 1. (Hemolysis) 1. Lung scarring
As
1. ‗Nausea‘
2. ‗Vomiting‘
3. ‗Diarrhea‘
1. lung scarring (Pulmonary
fibrosis)
2. Lung cancer
23
1.11 Objectives
To develop silica based adsorbents of high adsorption properties from the natural
sources like plants (Rice Husk).
To activate the adsorbents using various thermal procedures.
To develop less expensive chemically modified adsorbents form the agricultural
wastes for adsorption of pollutants (dyes, heavy metal ions etc.) from aqueous media.
To compare the adsorption efficiency of thermally and thermo-chemically modified
adsorbents prepared from Rice Husk.
To have a detailed physico-chemical investigation of the adsorption isotherms, the
adsorption kinetics and its thermodynamic behavior.
24
LITERATURE REVIEW CHAPTER#2
Abdi, et al. synthesized ZIF-8 (Zeolite Imida-Zolate Frame-work) as a MOF (Metal-
Organic Framework). The authors also have synthesized hybrid nano-composites which are
based on GO (Graphene Oxide) and CNTs (Carbon Nanotubes) through facile method at a
specific temperature. The dispersive forces and sufficient amount of GO, CNT substrate‘s which
were the major parts for development of composite into nano-scale MOFs, were investigated.
The MOF and hybrid nano-composites were characterized by FTIR, TGA, XRD, BET, and
SEM. The prepared materials were used as adsorbent for the removal of MG (malachite green)
from wastewater. The effect of various parameters like MOF loading quantity, solution pH,
adsorbent amount, temperature and initial dye conc. were analyzed to investigate the optimal
conditions. The kinetics of adsorption, equilibrium isotherm models, & thermodynamics
parameters were also investigated. Ethanol-washing could be applied for the regeneration of ZIF-
8 and its hybrid nano-composites. The hybrid nano-composites showed stable reusability for four
cycles. Hence it was concluded that the hybrid nano-composites are simple in synthesis, highly
effective, recyclable and stable in aqueous medium which enable these as excellent candidates
for the removal dyes from colored waste water (Abdi, et al., 2017).
Chaúque, et al. manipulated the nanofibers to enhance their adsorption efficiency for
ionic dyes from wastewater. The authors modified the PAN (poly acrylonitrile nanofibers) with
EDTA (ethylene diamine tetraacetic acid) and EDA (ethylene diamine). The modified EDTA-
EDA-PAN nano-fibers were analyzed by FTIR, XPS, SEM and BET techniques. Adsorption
equilibrium was investigated with Langmuir‘, Freundlich‘ and ‗Temkin adsorption isotherm
models which indicated that equilibrium data best follows the Freundlich isotherm model. The
modified PAN-nanofibers exhibited efficient sorption capacity = 99.15 and 110.0mgg−1
for MO
(methyl orange) and RR (reactive red.) from aqueous‘ solutions respectively (Chaúque, et at.,
2017).
Jiang et al. assembled ultra-light aerogels from cellulose nano fibrils into macro porous
honeycomb-cellular structures which are surrounded by meso-porous thin walls. Specific surface
is 193m2g
-1 and surface-carboxyl contents = 1.29 mmolg
-1 of the aerogel was investigated as
high that could be enough to remove cationic MG (Malachite Green) from aqueous solution. The
25
fast adsorption of MG was due to electrostatic interactions. The experimental data followed
pseudo-second order kinetics and monolayer Langmuir-model. It was investigated that
adsorption capacity was 212.7mgg−1
at 200mg/L of initial dye concentration, however high
percent removal of dye from aqueous medium was investigated at the dilute initial conc. of the
dye solution. Adsorbed dye into aerogel was de-sorbed in aqueous medium via rising ionic force,
presenting simplistic regeneration of the dye as well as aerogels (Jiang, et al., 2017).
Ali, et al. milled the ‗pomegranate‘ peel waste by using ball mills to make the particles
size of 90 μm and employed it as an adsorbent for the removal of lethal contaminants. Reactive
yellow dye and copper ions were removed from aqueous media using the prepared adsorbent. It
was investigated that the calculated amount of contaminants from the adsorption isotherm
models were in close concord with the practical one. The model predicted removal capacity was
209.7mg/g for the dye and 103mg/g for copper ions at optimum conditions (Ali, et al., 2018).
Fabryanty, et al. applied microwave heating for the production of bentonite-alginate
composite which was effectively applied as an adsorbent for the adsorption of dyes. The
irradiation was used for the formation of porous material to make easy an effective removal of
dye from aqueous solution. Three nano-composite models were synthesized by different ratios of
bentonite mass and sodium alginate mass. The adsorption efficiencies of bentonite-alginate nano-
composites were investigated for adsorption of CV (Crystal Violet) dye. The composites were
analyzed with FT-IR, SEM, XRD and nitrogen sorption method. Furthermore, the highest
removal capacity was inspected for the composite with high percentage of bentonite mass. The
adsorption capability of the composite was promoted at elevated temperature. (Fabryanty, et al.,
2017).
Goswami, et al. synthesized MTLAC (Matured Tea Leaf Activated-Carbon) and
MTLAC-SA (Matured Tea Leaf Modified Activated Carbon modified with Sulfonic Acid) from
agricultural waste product MTL (Matured Tea Leaf). The BET surface-areas of the prepared
material were investigated as 1313.4 m2g
-1 and 1169.3m
2g
-1 respectively. The prepared materials
were used for the removal of cationic and anionic dyes. The adsorption of RhB (Rhodamine‘ B)
MB (methylene‘ blue), BG (brilliant‘ green), CV (crystal‘ violet) and OG (orange ‘G) were
investigated on these adsorbents. It was inspected that the modified activated adsorbents
26
increased the adsorption efficiencies. The equilibrium data was best explained by Langmuir
isotherm. The kinetics data followed the ‗Pseudo-second-order‘ model. Thermodynamic studies
investigated that adsorption was endothermic and spontaneous‘ process (Goswami, et al., 2017).
Lipskikh, et al. studied that Synthetic azo-dyes are more frequently used to color the food
material. Excessive use of the azo dyes in food products has adverse effect on the living system
therefore; the azo dye should be used in controlled quantity. The authors employed the Volta
metric determinations of the azo dyes in the food materials. These methods are highly sensitive,
selective, speedy, and cheap (Lipskikh, et al., 2017).
Protein–surface interaction is crucial to the biocompatibility of bio-materials. PCBMA
(poly carboxy betaine methacrylate) grafted-silica was used for the adsorption of single protein
from human plasma. PCBMAs influence the surface charge and hence were grafted on the
surface of silica. PCBMA grafted-silica was prepared by Nitroxide mediated free-radical
polymerization. Results of the study showed that PCBMA grafted-silica was effective adsorbent
for protein adsorption and would be employed for biomedical applications (Abraham, et al.,
2012).
Polyvinyl pyrrolidone reduced-graphene oxide was made by advanced hummers‘ method
and was employed to remove Cu2+
from aqueous media. Adsorption capacity for Cu2+
ions was
investigated as 1689 mg g-1
which revealed that the adsorption process was physio-sorption
(Zhang, et al., 2014).
Alkan, et al. prepared, characterized, and demonstrated the thermal characteristics of
micro-encapsulated docosane with PMMA (polymethyl methacrylate). This material was used as
phase change for the storage of thermal energy. This material was analyzed by SEM‘ FT-IR
spectroscopy, DSC and TG,. It was investigated that the prepared material was efficient for the
thermal energy storage (Alkan, et al., 2009).
Arimi developed heterogeneous Fenton-catalysts from the naturally available cheap
materials for the removal of recalcitrants in MDW (molasses distillery wastewater). The
naturally available zeolites were modified with hydrochloric acid, sulphuric acid and nitric acid
and embedded the ferrous ions on them. The effects of temperature and pH on heterogeneous-
27
Fenton were investigated in presence of modified catalysts. The H2SO4-ferrous modified catalyst
removed 90% color- recalcitrants and 60% total organic carbon (TOC) using pellet catalyst
dosage = 150 g/L, with 2 g/L H2O2at 25 °C. The catalyst was pre-treated to the raw MDW which
had increased its biodegradability by 4%. The kinetic study of TOC removal was also
investigated which indicated that the kinetics of TOC depends on the operational temperature
(Arimi, 2017).
Przystas, et al. used the immobilized biomass of fungi-strains (Gleophyllumodoratum–
DCa, Pleurotus-(Ostreatus-BWPH), and Polyporus (picipes-RWP17) to investigate the efficiency
of decolorization on colored waste water. Immobilization of biomass enhanced the dye removal.
Diazo-dye was almost completely decolorized after twenty four hours by all samples of the fungi
strains. Comparatively high results of de-colorization for BG (brilliant green) were investigated
with BWPH‘ and RWP‘-17. Removal of color and reduction in toxicity was best inspected for P.
Picipes (RWP-17) (Przystas, et al., 2017).
Shaaban, et al. used NF (nano-filtration)-based separation technique for the treatment of
textile effluents. The effluents contained RB5 (reactive black) and DR60 (disperse) dyes. It was
investigated that NF-unit model E2 could remove 90% RB5 and 98 DR60 from the waste water
effluents. The effects of trans-membrane pressure, dye concentration, cross flow velocity and
temperature on dye removal were studied (Shaaban, et al., 2016).
Rahmana, et al. studied the adsorption of reactive dyes ‗H-EGXL‘ and ‗H-EXL‘ using a
variety of adsorbents prepared from clay. Both the reactive dyes were decolorized by synthetic
talc. Comparative study of the adsorption indicated that synthetic talc is more efficient adsorbent
than the other clay adsorbents. Kaolin and synthetic talc showed higher efficiency for the
adsorption of dyes in acidic media due to their high zeta potential. Equilibrium studied indicated
that equilibrium data followed the Langmuir model which revealed for monolayer coverage on
the homogenous adsorbent surface (Rahmana, et al., 2013).
Ghaly, et al. prepared ZnO/glass spiral (GS) by immobilization of ZnO on glass spiral
(GS) using facile method. The prepared sample was investigated with XRD, and SEM. SEM
inferred for the shapes of ZnO/glass spiral particles are rod-like. The prepared photo-catalyst was
28
used to investigate the degradation and decolorization of C.I. RR-120 (C.I. Reactive Red) under
the sunlight. The kinetics investigation of degradation and decolorization of RR-120 followed
the pseudo-first order mechanism. The degradation and decolorization of RR-120 was increased
by the addition H2O2 (Ghaly, et al., 2017).
Sun, et al. used diatomite as a carrier, to prepare nano-TiO2/diatomite composite-
material (NTID. Thermodynamic analysis of the prepared material was carried out by DSC
(differential scanning calorimetry) and TG (thermo gravimetry). The Structure of the prepared
composite material was investigated by XRD‘ SEM‘ and EDS. The photo catalytic properties of
the material were inspected by the degradation of Cu2+
in aqueous solution. Effects of different
investigational parameters such as pH, quantity of catalyst and initial.Cu2+
conc. for the removal
of Cu2+
were studied to optimize experimental conditions. 96.63% Cu2+
were removed from
solution by 10 mg/L of the composite material at 3 h irradiation under UV-light (Sun, et al.,
2015).
Adewuyi & Pereira investigated the sorption of Pb2+
on LCSA ―Luffacylindrica sponge‖
as adsorbent. LCSA was investigated by XRD ―X-ray diffraction analysis‖, SEM ―Scanning
Electron Microscopy‖, EDS ―energy dispersive spectroscopy‖, FTIR ―Fourier Transform
Infrared‖ spectrometer, TGA ―Thermo-gravimetric analysis‖, and BET analyzer. The adsorption
of Pb2+
on LCSA was investigated aschemi-sorption and the thermodynamic study indicated the
process was exothermic (Adewuyi & Pereira, 2017).
Gonte & Balasubramanian used the Hyper-crosslinked styrene maleic acid copolymer-
beads for the adsorption of heavy metal ions. The polymer was characterized by Scanning
Electron Microscopy (SEM) which revealed for its porous nature. The metal uptake was
considered due the Carboxylic groups. The enhanced uptake of metal ions was due to high
porous nature of the adsorbent on which the adsorption was driven by physico-chemical process.
Equilibrium study was best explained by Temkin and Freundlich adsorption isotherm models
with R2> 0.99. Adsorption data followed the ‗pseudo-first‘ and ‗pseudo-second‘ order kinetics
models (Gonte & Balasubramanian, 2016).
29
El-Gendy& El-Bondkly collected wastewater samples from different industries in Egypt
which demonstrated high levels of Ni2+
, Cr6+
, and Zn2+
ions. These metal ions are the most toxic
to wildlife and humans. The authors derived 69 Actinomycete isolates to evaluate their
biosorption capacity for metal ion from aqueous solution. MORSY2014 and MORSY1948 were
investigated as the most active and efficient biosorbents. These two strains were investigated
from their chemotype and phenotype characterization as the member Nocardia and Nocardiopsis
respectively. The dead-biomass of MORSY1948 could remove Ni2+
, Cr6+
, and Zn2+
ions from
aqueous solution as 87.90%, 84.15% and 63.75% respectively. Whereas the dead-biomass of
MORSY2014 could remove Ni2+
, Cr6+
, and Zn2+
ions from aqueous solution as 93.53%, 95.22%
and 90.37% respectively (El-Gendy & El-Bondkly, 2016).
Loqman, et al. studied the removal of ‗crystal violet‘ dye from aqueous media by using
the local clay of Morocco as adsorbent. The adsorbent was analyzed by ‗XRD‘, ‗IR-
spectroscopy‘, ‗XRF‘, ‗SEM‘, ‗BET‘ analysis. Optimum experimental conditions were
investigated. The maximum uptake capacity of the dye at optimum conditions was investigated
as 81.62% (Loqman, et al., 2017).
Zhao, et al. modified peanut husk with cationic surfactant (hexadecyl pyridinium
bromide)which was used as an adsorbent for the elimination of Light Green (LG) dye from
aqueous media. Adsorption of dye was analyzed by UV-spectrophotometer at maximum
wavelength of 660 nm. Maximum dye removal was attained at pH range = 2−4. Addition of
NaCl and CaCl2 to the solution decreased the adsorption efficiency of the adsorbent (Zhao, et al.,
2017).
Pourfadakari, et al. obtained nano-sized cellulose from RH (rice husk) and employed it as
an adsorbent to remove Cr(VI) from waste water. At optimum conditions, 92.99% Cr(VI) was
adsorbed by the adsorbent. The equilibrium data was best fitted to Langmuir‘s adsorption
isotherm with R2=0.998. Kinetic data was best fitted to ‗pseudo-first order‘ kinetic model with
R2=0.993. The negative ΔG values suggested that the adsorption process was spontaneous
whereas, ΔH values are positive which inferred for endothermic process (Pourfadakari, et al.,
2017).
30
Shalaby, et al. prepared mesoporous adsorbent via the recycling of water-treatment
sludge and rice husk was used as textural modifier. The mesoporous adsorbent was used to
remove Pb2+
, Ni2+
, rosaniline dye and chlorine from waste water. Initial concentration of dye and
adsorbent textural structure could have an effect on the adsorption power. Desorption of dye took
place on pH = 8 which inferred for the regeneration of adsorbent. Adsorption of chlorine was
controlled by CEC (cation exchange capacity). It was also investigated that the radii of metal
cations could affect their adsorption (Shelby, et al., 2017).
Stolarska & Garbalinska modified the building materials like ceramic bricks, autoclaved
aerated concrete, silicate bricks, cement–lime mortar, cement mortar, and cement mortar with
polypropylene fibers. The prepared materials were different from each other due to their porous
structures. These materials were subjected to moisture sorption at different temperatures i.e. 5°C,
20°C and 35°C. Equilibrium moisture-sorption was investigated for the material at eighteen
different temperatures. Different experiments were performed to achieve the matching results of
experimental with that of theoretical (Stolarska, & Garbalinska, 2017).
Chinnakoti, et al. synthesized nano C-alumina through low cost and simple method in
which surfactant assisted solution was combusted. The synthesized material was tested with
‗XRD‘ and ‗FESEM‘ characterizations to investigate their size, phase and morphology. BET was
employed to determine the surface properties. Nano C-alumina was used for the adsorption study
of fluorides from aqueous media through batch adsorption mode. The defluoridation was
investigated under various experimental conditions. It was investigated that 96 % fluoride was
adsorbed on C-alumina at pH = 4. The adsorption equilibrium was reached in two hours. The
defluoridation data was also analyzed with various isotherm and kinetic models (Chinnakoti, et
al., 2017).
Selim, et al. modified the surface of glauconite (Egyptian phyllosilicate mineral) and
used it to adsorb the metal ions. It was investigated that modified glauconite enhanced the
adsorption of Zn2+
from 96.67% to 99% and that of Pb2+
from 84% to 94%. The equilibrium data
was subjected to ‗Langmuir‘, Temkin, ‗Freundlich‘, and ‗Dubinin-Radushkevich models‘.
Experimental data for the adsorption of Pb2+
on the modified glauconite was investigated as best
fitted to the Langmuir model which inferred for chemical adsorption. The separation factor for
31
Zn2+
and Pb2+
was investigated as 0.0324 and 0.13207 respectively, which supported the
favorable sorption process (Selim, et al., 2017).
Tavakkoli, et al. proposed a sensitive and simple method which consists of small-column
filled with MWCNTs ―multi-walled carbon-nanotubes‖ in combination with GFAAS ―graphite
furnace atomic absorption spectrometry‖ intended for the investigation of As(III) in aqueous
solution. The effects of experimental parameters like pH, adsorbent dose, adsorbate
concentration were investigated. A quantitative sorption was investigated which could be
desorbed in 3 mol/l HNO3solution made in acetone. This method was successfully applied to
determine As(III) in aqueous media (Tavakkoli, et al., 2017).
Moawed, et al. described a simple, inexpensive and rapid way to develop a new
biosorbent. The material was prepared from miswak-fibers which were modified with NaOH.
The prepared adsorbent was used for the removal of metals from various samples of water. These
metals were completely removed at pH below 7. Sorption capacity of the biosorbent for Co-II,
Fe-III and Ni-II were investigated as 0.15, 0.54, and 0.24 mmol/g, respectively (Moawed, et al.,
2017).
Samadi, et al. used chelating resins for adsorption of Cu2+
from water. The modified
resins were treated with 1, 2-diaminoethane along with ultrasonic irradiation to prepare a nano
sized chelating-resin to removeCu2+
from aqueous media.Cu2+
were determined by using co-
polymers derivative resins of poly‘ SMA ―styrene-alternative-maleic anhydride‖ and ―atomic-
absorption spectroscopy‖. This technique was inexpensive, responsive, simple, and rapid.
Adsorption of Cu2+
was investigated on different parameters such as pH, agitation speed, time,
initial conc. of Copper-II ions and adsorbent dose. The resins showed better tendency and
selectivity for Copper (II) ions even in the high acidic medium. This resin was also useful for the
adsorption of Cu(II) from the industrial waste-water.(Samadi, et al., 2017).
Cai, et al. synthesized phytic acid modified magnetic-CoFe2O4 (PA/CFO) composite by
facile one-pot microwave-hydrothermal technique. The coating of Phytic acid (PA) onto the
CFO-NPs was confirmed by FT-IR, SEM, TEM, and XRD pattern. XRD analysis indicated that
the addition of PA to magnetic-CoFe2O4, decrease its crystallinity whereas the TEM and SEM
32
images inferred that the heterogeneous particle size of the material decreases with the increase
in the additive amount of Phytic acid into the sample which tends to form the particles of
uniform size. The surface of PA/CFO is negatively charged which was used for selective
adsorption of cat-ionic dye like MB ‗methylene blue‘ and metal cat-ions such as Mg2+
, Zn2+
,
Cu2+
and Pb2+
. The adsorption capacity for these metal ions was investigated as 227.3, 126.4,
156.9 and 666mgg−1
respectively. The ferrite-based composite magnetic adsorbent was
considered as efficient adsorbent for adsorption of cationic dyes and ‗metal‘ cat-ions (Cai, et al.,
2107).
Shajahan, et al. considered the Chitosanas a chelating-agent for high adsorption capacity
of dyes, proteins and metal ions. The authors prepared and characterized a variety of‗ fungal
chitosan-nanoparticles‘ ―FCI-1‖ to ―FCI-6 NPs‖ via ionic gelation technique. The adsorption
efficacy for various dyes was investigated. Morphology of ‗FCI-1‘ was inspected as spherical.
Electron micrograph indicated that ‗FCI-1 NP‘ was steady for long time if stored at 4°C.
Removal of various dyes like RBB, DR, NBB, MO, and CSB on ‗FCI-1‘ and ‗FCI-1 NPs‘ was
investigated using spectrophotometry. Results of the adsorption process indicated that FCI-1 NPs
are efficient sorbents (Shajahan, et at., 2017).
Wawrzkiewicz, et al. synthesized meso-porous ‗silica-alumina oxide‘ ―97% SiO2 and 3%
Al2O3‖and used it for the removal of ‗acid orange‘, ‗reactive black‘ and ‗direct blue‘ dyes from
wastewater. The synthesized material was also used for the adsorption of Co2+
, Zn2+
Cu2+
and
Ni2+
from wastewater. Batch mode of adsorption was employed. Effect of various parameters
like agitation time, initial dyes/metal ions concentrations, salt and anionic surfactant were
studied. Equilibrium data was best fitted to Freundlich model. Potentiometric titration indicated
that the adsorption of metal cat-ions and dyes could control the morphology of electric double
layers on the prepared adsorbent interface. Results indicated that the prepared mixed oxide was
efficient adsorbent to remove heavy metal cat-ions form wastewater (Wawrzkiewicz, et al.,
2017).
Jung, et al. synthesized two type of frame-works, ‗Al-FA‘ ―aluminum-fumaric acid‖ and
‗Al-SA‘ ―aluminum-succinic acid‖ which were applied as adsorbent for the removal of azo-dyes.
Adsorption results indicated that Al-SA exhibited more efficiency than Al-FA. The adsorption
33
capacities of Al-SA for the mono and di-azo dyes were investigated as 559.28 and 332.48 mg g-1
respectively (Jung, et al.,2017).
Rashid, et al. investigated the factors affecting the adsorption efficiency of chitosan-
metal complex adsorbent which include various metal-centers cross-linking degree and different
types of metal salts. Chitosan-Fe(III) complex could remove 100% of different dyes in just ten
minutes with efficiency of 349.22 mg g-1
(Rashid, et al., 2017).
Sham & Notley investigated graphene exfoliated with surfactants to remove the organic-
dyes from waste water. ‗Zeta potential‘ analysis showed that graphene particles possess exterior
charges which are dominated by exfoliating surfactant charges that could enhance the adsorption
of dyes. The surface of graphene-particles could be prepared either negatively or positively
charged to adsorb cationic or anionic dyes selectively from aqueous media. Organic dyes were
adsorbed from wastewater was due to ionic interaction between dye molecules and adsorbed
surfactants. The maximum adsorption of dye was inspected for cationic methylen-blue on the
surface of graphene exfoliated with an-ionic surfactants, SDS ‗sodium dodecyl sulfate‘. It was
investigated that variations in the experimental parameters have significant effect on the removal
of dye on ‗SDS exfoliated graphene‘.High uptake capacity of the adsorbent was investigated as
782.3mg g-1
which suggested that the prepared adsorbent has excellent adsorption
properties(Sham &Notley, 2018).
Jin, et al. prepared Ni/PC-CNT [‗Nickel nanoparticles‘ embedded in porous-carbon and
‗carbon nano-tubes‘] hybrids through an easy carbonization method by‗Ni/Zn-MOF‘. The
magnetic Ni nano-particles were encapsulated in the porous carbon/carbon nano-tube after
carbonization. It was investigated that prepared composites contain surface area = 999 m2 g
.-1
which exhibited very high uptake capacity for the adsorption of MG ―Malachite Green‖, CR
―Congo Red‖, Rh B ―Rhodamine B‖ and MB ―Methylene blue‖ (Jin, et al., 2018).
Li, et al. developed adaptable biosorbent ―CH-PAA-T‖ through heat cross linking
chitosan and poly-acrylic acid, which indicated outstanding adsorption capacity for the removal
of oil‘ heavy metal ions and toxic dyes from aqueous media, simultaneously. The uptake
capacities for methylene Blue and Cu2+
were investigated as 990.1 and 135.9 mg g−1
34
respectively. The CH-PAA-T is highly selective for the adsorption of organic dyes, and hence
could be used to separate the mixture dyes. CH-PAA-T could be recycled up to ten times with
almost the same efficiency. Such versatile bio-based adsorbent could be efficiently used for the
waste water purification (Li, et al., 2017).
Masoomi, et al. synthesized Cd2+
-based organo-metalic structure ‗TMU-7‘, through
sono-chemical technique. The prepared sample was analyzed with SEM and XRD analysis.
Moreover, TMU-7 was evaluated to adsorb N2 and Congo red (Masoomi, et al., 2017).
Du, et al. prepared ZIF-67 ‗Zeoliticimidazolate frameworks-67‘ by electrochemical
processing. The product was used to adsorb different organic dyes. It was investigated that‗ZIF-
67‘ has high uptake capacity for certain dyes and could remove some of the organic dyes
selectively from a mixture of dyes. The possible adsorption mechanisms were proposed and
tested as electrostatic interactions, hydrogen bonding, and coordination interactions (Du, et al.,
2017).
Wu, et al. designed a multifunctional scavenger to purify the water. The authors
described a sophisticated method for the preparation of an inorganic/organic-composite material
for the simultaneous removal of disinfection, metal cat-ions and anionic dyes. The prepared
sample has a stable morphology with covalent bonding between MS (magnetic silica) core and
poly ethylenimine derived QAC (quaternary ammonium compound) corona. The sample was
characterized by SEM, TEM, XRD,FT-IR, EDX (energy dispersive, X-ray), TGA (Thermo
gravimetric analysis) and zeta potential. QAC-MS sample showed superior performance for the
adsorption of acid fuchsine and Cu2+
and could be considered as promising material to apply for
water purification (Wu, et al., 2018).
Qiu, et al. modulated ‗UiO-66‘by the addition of HCl or CH3COOH in the forerunner
solution. The resultant material has defined octahedral geometry with elevated surface area (892-
1090 m2/g). Various ‗UiO-66‘ were applied to adsorb an-ionic and cat-ionic dyes selectively.
The acid-promoted UiO-66 indicated high selectivity for an-ionic dyes. The uptake capacities of
methyl orange and methylene blue were investigated as 84.8 mg g-1
and 13.2 mg g-1
,
correspondingly. The mixed dyes (anionic and cationic) adsorption on the UiO-66 proved its
35
selectivity for the an-ionic dyes. The ‗Zeta potential‘ of ‗UiO-66‘ is more positive which also
inferred for its selectivity towards anionic dyes (Qiu, et al., 2017).
Liu, et al. fabricated MS-NiFe2O4 (Functionalized magnetic microsphereNiFe2O4) with
3-D hierarchical porous structure using urea as a modifier by one pot solvothermal method. The
MS-NiFe2O4 showed excellent simultaneous adsorption of metal cat-ions (Cu2+
, Cr3+
, Cd2+
and
Zn2+
ions), and FQs (fluoroquinolone), CIP (ciprofloxacin, ENR (enrofloxacin) and NOR, (nor-
floxacin). The adsorbent could easily be recycled by using external magnetic field. The
adsorption efficiency of the targets was reached upto 80% in 60 min at pH = 5. The adsorption of
one contaminant, the competitive removal of multiple contaminants, the simultaneous and
sequential removal of the co-existent organic contaminants were investigated in detail onto MS-
NiFe2O4. The possible adsorption-mechanism of targets onto MS-NiFe2O4 was also determined
(Liu, et al., 2018).
Fan, et al. investigated adsorption of different organic dyes on ―NH2-MIL-125(Ti)‖
(NH2-functionalized titanium-based organo-metalic framework). The authors first synthesized
and characterized ―NH2-MIL-125(Ti)‖ and ―MIL-125(Ti)‖. The Ti-MOFs were magnetized
facilely by adsorbing Fe3O4-nanoparticles by Lewis acid and Lewis base interactions. The
adsorption investigation of anionic, cat-ionic, and vat dyes showed that the, π-π stack
interactions, electrostatic interaction have significant effect on the adsorption.‗NH2-MIL-
125(Ti)‘ could provide higher adsorption capacity. The kinetics and equilibrium studies
recommended that adsorption of methylene blue on ‗Ti-MOFs‘ followed the ‗pseudo second
order‘ kinetic model. The thermodynamic studies inferred for spontaneous process (Fan, et al.,
2018).
Ma, et al. synthesized a DNHs ‗double network hydrogel‘ with a base of WCFs (waste
cotton fibrics) and ‗polyacrylamide‘ [‗Cellulose/PAM-DNHs‘]. The prepared material was used
for the adsorption of heavy metals. The DNHs exhibited fast kinetics and the sorption
equilibrium was achieved in just 5 min. The DNHs possess efficient adsorption properties and
could be recycled. Therefore, it is an important adsorbent due to resource sustainability and
environmental friendly (Ma, et al., 2018).
36
Tangaraj, et al. investigated the adsorption properties of ―CTAB-saponite and CTAB-
montmorillonite‖ with cat-ionic surfactants, for fluorescent dyes like Rhodamine 640, sulfo-
rhodamine B (SR), perchlorate Rhodamine (Rho), and ‗Kiton red-620‘ (KR). The equilibrium
data was best fitted to the Langmuir model. The adsorbed dyes on the adsorbent were also
highlighted with XRD, TEM, fluorescence measurements and thermal analysis (Tangaraj, et al.,
2017).
Dutta, et al. synthesized the ―amorphous carbon-nanotubes‖ by low temperature ‗solid-
state‘ reaction. CNTs were employed for the adsorption of two fabric dyes, MO ‗Methyl
Orange‘and RB ‗Rhodamine B‘ from wastewater. Adsorption experiments were performed under
different conditions. Experimental results were subjected to ‗Freundlich‘, ‗Langmuir‘ and
‗Temkin‘ models. The kinetics data was best fitted to ‗pseudo first-order‘ mechanism (Dutta, et
al.,2018).
Shaban, et al. used serpentine (a natural layered magnesium-silicate mineral) to
investigate the adsorption of toxic dyes (methylene blue, Congo red) and Cr6+
from industrial
waste water. Adsorption of contaminants was studied at variable experimental conditions like
contact time, initial contaminant concentrations, serpentine dosage and the initial solution pH.
The equilibrium time for ‗Congo red‘, ‗methylene blue‘, and Cr6+
was studied as 180, 240, and
480 min, respectively. The equilibrium data of ‗methylene blue‘ and Cr6+
followed the Langmuir
isotherm model which described monolayer adsorption for these contaminants. The adsorption
data of ‗Congo red‘ dye fitted well to Freundlich isotherm, which revealed for its multilayer
formation. The adsorption of methylene blue was more efficiently inspected in the basic pH
value whereas that of ‗Congo red‘ and Cr6+
was favored in the acidic media. Thermodynamic
investigation suggested that adsorption of methylene blue was endothermic whereas that of
‗Congo red‘ and Cr6+
was exothermic. Acid and thermal modification of serpentine had
improved its adsorption properties to a high degree. Serpentine of 15% concentrated HCl leached
and activated at 20°C was investigated as efficient adsorbent (Shaban, et al., 2018).
Sabet, et al. doped Cd2+
into ZnO crystal-lattice by hydrothermal method. Effect of
different parameters such as reaction time, surfactant, temperature and cadmium source on the
size and morphology of the product was studied. Results of the study showed that each parameter
37
could significantly affect the size and morphology of the product. The ZnO band gap of the
product can be changed by different parameters like cadmium source and particle size as
investigated by the optical properties. The surface activity of nanostructures was inspected by
removing Pb2+
from water. The product was analyzed by XRD‘ EDS‘ SEM‘ and U.V–Visible
spectra (Sabet, et al., 2018).
Sakthisharmila, et al. employed electrochemical technique for the treatment of direct
green-1 (DG-1) dye using ‗metal hydroxides/oxy-hydroxides‘. Various experimental conditions
were employed to determine the maximum adsorption efficiency for the removal of dye. The dye
removal by metal hydroxides was attributed to ‗partial-degradation‘ of azo-bond which was
coagulated on metal hydroxides. This was supported by FTIR, UV-visible, and SEM-EDX
spectroscopic analysis of electro-coagulated flocks and treated water (Sakthisharmila, et al.,
2018).
Stawiński, et al. modified vermiculite to produce an efficient, inexpensive and stable
adsorbent for the adsorption of dyes/metal ions. The adsorbents were activated by three methods
to enhance their uptake capacities. For this purpose the adsorbents were treated with acid, base
and simultaneously with acid-base. Adsorbents were used to test their adsorption capacities for
the adsorption of cationic dyes and Cu2+
. The simultaneous acid/base-treated adsorbent exhibited
better uptake capacity than that of untreated adsorbent however; its uptake capacity for Cu2+
was
similar to that of starting materials. The base treated adsorbent exhibited better adsorption
capacity for metal ions. Moreover, the adsorbent could be regenerated and reused for more
adsorption/desorption cycles. The adsorbed dyes from metal ions could be separated by using
ethanol/NaCl & 0.05 M HNO3 respectively as eluents (Stawiński, et al., 2017).
Sherlala, et al. modified graphene oxide by using organic materials. The organo
functionalized grapheme oxide composites were used for adsorption of metals ions, the authors
investigated the effect of different operational parameters, adsorption kinetics, mechanisms and
stability of the adsorbent (Sherlala, et al., 2018).
Pal, et al. modified CS (chitosan) beads by using SDS (sodium dodecyl sulfate). The
suitable concentration of SDS was selected for the formation of surfactant bi-layer on the surface
38
of CS. The prepared modified beads were named as SMCS (surfactant-modified chitosan) beads
which were used as adsorbents. The adsorbent was characterized by SEM and XRD. The SMCS
beads were employed for removal of Cd2+
from wastewater. Results of adsorption study of
SMCS beads indicated that adsorption capacity of SMCS was three times greater than simple CS
beads. The uptake capacity was investigated as 125 mg/g. 100% of the Cd2+
ions could be
removed from dilute concentration (10-30 mg L-1
) of metal cat-ions whereas the removal
capacity was decreased to 50% for high concentrated solutions (40-100mg/L) (Pal, et al., 2017).
Saad, et al. fabricated ―ZnO-Chitosan coreshell‖ in nano-composite and employed it to
adsorb Cd2+
, Cu2+
and Pb2+
from contaminated water. The prepared material was characterized
by ‗TEM‘, ‗EDX‘, ‗FE-SEM‘, and ‗FTIR‘ which inferred for the nano sized adsorbent particles
with round shape. The optimum adsorption efficacies for Cu2+
, Pb2+
and Cd2+
, were investigated
at pH 4.0, 6.0& 6.50, correspondingly (Saad, et al., 2018).
Li, et al. synthesized composite-adsorbent which was multifunctional material. This
material has high potential for anionic exchange. The material was prepared by hybridization of
LDH ―layered double hydroxides‖ and FA (folic acid). It was investigated that the functional-
groups could be effectively attached on the surface of LDH. Therefore, ability of anion exchange
remained and adsorption efficiency of Orange-II could arrive at 1.9mmolg-1
, this is
approximately equal to that of pure LDH. Moreover, the uptake capacity for ‗Cu2+
, Ni2+
Pb2+
and
Cd2+
‘ was investigated as 2.25, 0.99, 0.98 and 0.16mmol/g respectively. Furthermore, Orange II
& toxic metals could be efficiently adsorbed by the prepared adsorbent (Li, et al., 2018).
Yang, et al. employed the negatively charged adsorbent for the adsorption cationic dyes.
The electrostatic interaction made it an efficient adsorbent for the removal cationic dyes. The
cat-ionic dyes which have been adsorbed on the surface of negatively charged adsorbent include
crystal violet, light yellow, methylene blue and acid green (Yang, et al., 2108).
Gong, et al. investigated the influence of pyrolysis on stabilization of heavy-metals in the
plant residue obtained after phyto-remediation. Ramie residues were collected after phyto-
remediation of metals contaminated sediments, which were pyrolyzed at various temperatures
(300 to 700 °C). It was investigated that pyrolysis could enhance the stabilization of, Cr, Cd Cu,
39
Zn, and Pb in the ramie residue by transforming the acid soluble fractions of metals into residual
forms and hence the TCLP-leachable metal contents are decreased. The pyrolyzed product was
used as adsorbent which indicated excellent adsorption ability for methylene blue with
adsorption capacity = 259.27 mg/g. This study investigated that pyrolysis could be employed for
the stabilization of heavy metal ions into plant residue obtained after phyto-remediation, and the
products can be reutilized for the adsorption of dyes (Gong, et al., 2018).
On the basis of literature studied, it is cleared that few bio-adsorbents such as cellulose
etc., has been used continuously for the removal of dyes and heavy metals from aqueous media.
But cellulose is mostly consists of carbon, hydrogen and oxygen. Usually considerable mass
containing oxygen and hydrogen is lost during the preparation of charcoal. Moreover,
carbonization of cellulose needs very high temperature (T > 800 °C) to prepare activated carbon;
therefore, the adsorbents prepared from cellulose are expensive. In contrast, the Rice Husk (RH)
is consisting of SiO2 along with organic texture. SiO2 is thermally more stable than cellulose
which avoids the mass loss during the preparation of Rice Husk Char (RHC). Furthermore, the
RHC can be prepared at very low temperature as compared to the activated carbon (T < 500 °C).
Similarly, RHC and rice husk ash (RHA) particles have very high surface energy due to which
they combined with each other and form large aggregates and hence the availability of active
sites decreases when these particles were treated for their applications. They showed poor
dispersion as a result, the targets were not fully achieved. These problems might be solved by
subjecting the particles to physical methods like ball milling method, high power sonication and
mechanical stirring to reduce the particle size and increase the surface area of the adsorbents.
Furthermore, the adsorbents were chemically modified with KOH to enhance the adsorption
efficiencies of the adsorbents. In addition to these, the present work also focuses on the
physicochemical investigations from academic point of view as well.
40
EXPERIMENTAL CHAPTER # 3
3.1 Materials
The source material, ―Rice Husk‖ was collected from the rice processing mills of the
local area of district Mardan Khyber Pakhtunkhwa Pakistan. The textile dyes (Orange G and
Titan yellow) and heavy metal (Pb2+
) salts were obtained from the Merks/Sigma Aldrich, The
analytical grade chemicals (NaOH, HCl, KOH etc) were used with no additional refining. De-
ionized water was subjected for the preparation of stock and operational solutions of dyes and
heavy metal ions. Pyrex glass wares were used for keeping solutions and running out reactions.
Muffle Furnace (PT-1200M) and Tube Furnace (PT-1200T) were used for the preparation and
modification of the adsorbents. UV,-Visible Spectrophotometer (Perkin E
,lmer Lambda
,-25) and
atomic absorption,
Spectrophotometer, (Perkin E
,lmer AAnalyst
,-700) were used for the
determination of residual concentrations of dyes and metal ions respectively. A brief description
of the dyes used is given as follow.
Orange G (OG) Dye: Orange G (orange gelb) is an azo dye. Its serial no = C.I.
16230, chemical formula = ‗C16H10N2Na2O7S
,2 and molar
, mass = 452.38
,g/mol. OG is
carcinogenic dye (Carson, et al., 2009). OG has (–N=N–) chromospheres bonded with
aromatic moieties (Halima, et al., 2008). Its structure formula is:
Figure 3.1 Structural Formula of Orange G Dye
Titan Yellow (TY) Dye: TY is an azo dye. It‘s serial no. = C.I. 19540. Chemical
name = Titan Yellow, chemical formula is C28H19N5Na2O6S4 and molar mass = 695.720
g/mol. CB Number =CB2224187, Melting point = >250°C, solubility, = 29g/l, Color-
index =19540, shape = powder, color =Yellowish-brown, pH range =12(yellow)-13(red),
41
pH =5.1 (10g/l, H2O, 20℃), Water Solubility = almost transparency, λmax = 398-405nm,
Merck =14,9310, Stability = Light sensitive, Incompatible with strong oxidants. Major
Application = Display device, incandescent electric lamps, thin-film device, optical
sensors, inks, pencil leads, photoreceptors, lithographic process, adhesives, paints,
molding materials, steel plates, plastic materials, detection of albumin, treatment of
amyloidosis disorders, treatment of apolipoprotein E-related diseases. (Russo, et al.,
2013). Its structure formula is:
Figure 3.2 Structural Formula of Titan Yellow Dye
3.2 Preparation of Adsorbents from Rice Husk
3.2.1 Preliminary Treatment of Rice Husk (RH) for the Preparation of Adsorbents
The Rice Husk was dispersed in doubly distilled water and agitated with magnetic stirrer
for one hour to remove the water soluble contents. The dispersed, solid was then separated from
water and washed by 1 mol/L of HCl solution through agitation with magnetic stirrer for 30
minutes. The resulting dispersion was filtered to separate solid from liquid, the solid obtained
was dispersed in 0.5 molL-1
of NaOH solution and stirred through magnetic, stirrer for 30
minutes at 25°C. The dispersion was filtered to separate the solid from solution and the obtained
solid was washed through de-ionized water and thereafter this product was dehydrated inside
electric oven,
at 60◦C, for four hours. This product was used for the preparation of different
adsorbents.
42
3.2.2 Preparation of ‗Rice Husk Char‘ (RHC)
Four samples of the ‗Rice Husk Char
‘ (RHC) were prepared from the source material by
thermal treatment. For this purpose a known amount (10 grams) of the Rice Husk (as prepared in
section 3.2.1) was kept in furnace at different temperatures ‗300◦C, 350
◦C, 400
◦C, and 450
◦C‘ for
one hour in each experiment, which results into blackish type products, known as the Rice Husk
Char (RHC). Each of these materials was grinded to find powdered and sieved through a mish of
250 μm and stored in airtight bottle that were used separately as adsorbent for adsorption of dyes
and heavy metal form wastewater. Experimental results indicated that adsorption efficiency of
adsorbent enhanced at elevated temperature from 300◦C to 400
◦C and thereafter no significant
change was inspected. Hence further preparation/activation of RHC was carried out at 400◦C.
3.2.3. Preparation of KOH Modified Rice Husk Char (KMRHC)
15 grams of RHC (prepared at 400◦C as mentioned in section 3.2.2) was dispersed with
3g of solid KOH (5:1 ratio) followed by the addition of 30ml distilled water and was kept on
magnetic stirrer at 80 ◦C for 3 hours. A paste obtained was dried and grinded which was divided
into five parts; each of these was kept in furnace at different temperatures [300°C,350°C,
400°C,450°C, and 500°C] for one hour. The prepared materials were cooled and dispersed with
distilled water and the pH of this suspension was adjusted as 7 by adding small quantity of HCl
solution. Thereafter the solid material was separated from liquid and was dried at 120◦C for two
hours. These materials were grinded to fine powder, sieved through a mesh of 250 micro-meters
and stored in airtight bottles, labeled as KMRHC with the prescribed temperatures. The prepared
materials were employed to adsorb dyes/metal from water. It was investigated that adsorption
efficiency of KMRHC enhances by increasing the activation temperature from 300◦C
to450◦C.Furtherincrease in the activation temperature have no significant effect on the uptake
capacity of dyes and heavy metals. Hence 450◦C was considered the optimum activation
temperature for KOH Modified Rice Husk Char (KMRHC).
3.2.4 Preparation of Rice Husk Ash (RHA)
A known quantity of the Rice Husk (as prepared in section 3.2.1) was burnt in open air.
20 grams of the ashes obtained, were kept in the tube furnace at 700°C for one hour. The product
43
obtained was whitish in color which was named as Rice Husk Ash (RHA). It was grinded and
sieved through a mesh of 250μm and was used as adsorbent for adsorption of dyes/heavy metals
from aqueous‘ media.
3.2.5 Preparation of KOH Modified Rice Husk Ash (KMRHA)
A known amount (15 grams) of RHA (as prepared at in section 3.2.4) was treated with
KOH according to the procedure mentioned in section 3.2.3. The dried product obtained was
grinded and divided into five parts, each of these were kept in furnace at five dissimilar
temperatures ―600◦C, 650
◦C, 700
◦C, 750
◦C and 800
◦C‖ for one hour. Each of the prepared
material was cooled and dispersed in distilled water separately, 0.1M HCl solution was added
drop wise until the pH of suspension became 7 and thereafter the solid materials were separated
from liquid and dried at 120◦C for two hours. These materials were grinded to fine powder,
sieved through the same mesh as mentioned in section 3.2.3, stored in airtight bottle separately
and labeled as KMRHA (with their prescribed temperature). Each of these materials was used to
remove dyes/heavy metals from aqueous media separately. The uptake capacity of KMRHA was
examined to be increased with activation temperature from 650◦C to750
◦C. However, further
increase in the activation temperature has no significant effect on the adsorption efficiency of
dyes. Hence 750◦C was considered the optimum activation temperature for KOH Modified Rice
Husk Ash (KMRHA).
3.3. Adsorbate
1000 mg/L solution was prepared by the addition 0.1g of dye in 100 ml de-ionized. This
solution was used to prepare working and standard solutions i.e. 20mg/L, 40mg/L, 60mg/L,
80mg/L, 100mg/L and 120 mg/L. In a similar way 1000 mg/L of metal ions solution was
prepared and diluted to make working solutions of different concentrations (50mg/L, 100mg/L,
150mg/L, 200mg/L, 250 mg/L and 300 mg/L). 0.1M HCl and 0.1 M NaOH solutions were
employed to adjust the pH.
44
3.4 Adsorption Experiments for the Investigation of Dye
3.4.1 „Equilibrium Study
‟
Adsorption of dye on the adsorbent prepared from RH (2g/L) was investigated at
different interval of time.50 ml variable conc. of dye solutions (20-120 mgL-1
) in a 250 ml
beaker at stirring speed of 240 rpm for 90min at 303k was employed till the equilibrium was
established. Equilibrium dye conc. (Ce) was investigated by analyzing the residual concentration
of dye after the adsorption at a time interval of 10 minutes using UV- Visible Spectrophotometer.
Adsorption capacity and percent adsorption of dye was calculated by using equation (3.1) and
(3.2).
(3.1)
(3.2)
(3.3)
Where, qe= Adsorption capacity‘ ‗mg/g‘, V=Volume of dye solution in Liters, Co and Ce
is the initial and equilibrium dye concentration ‗mg/L‘ respectively and m =adsorbent dose (g).
3.4.2 Effect of ‗Adsorbent Dose‘ on Adsorption of Dye
The adsorbent dose was varied from 1.0 to 5 g/L for 50 ml of 80 mg/L of dye solution
with stirring speed of 240 rpm, for equilibrium time. The residual concentration of dye was
analyzed after solid-liquid separation by using UV-Visible Spectrophotometer. The adsorption
capacity and percent adsorption of dye was calculated by using equation (3.1) and (3.2).
3.4.3 Effect of pH on ‗Adsorption‟ of Dye
50 ml of 80 mg/L of dye solution was taken in a 250 ml beaker with the addition of 2g/L
of the adsorbent. This mixture was stirred at 240 rpm for equilibrium time over a pH range of
2—10 (2, 4, 6, 8, 10). 0.1M ‗HCl
‘ and 0.1M
‗NaOH
‘ solutions were utilized for the adjustment of
45
pH. Separation of liquid from the solid, determination of residual dye concentration, calculation
of uptake capacity and percent adsorption was carried out according to the method mention in
3.4.1.
3.4.4 Effect of „Temperature‘ on Adsorption of Dye‘
The effect of ‗temperature on the ‗adsorption process was examined in the temperature
range of 303-343K, The other experimental conditions were; Initial dye concentrations was
80mg/L, equilibrium agitation time, stirring speed = 240 rpm, pH = 3.5 for TY and 4 for OG dye
and adsorbent dose was 2g/L. After completion of each experiment the suspension was filtered to
separate the solid from liquid and the residual dye conc. was analyzed. The adsorption capacity
and percent adsorption of dye were determined.
3.5 Adsorption Experiments for the Investigation of Metal Ions
3.5.1 Equilibrium Study of the Adsorption of ‗Metal Ions‘
The metal ions adsorption on adsorbent (2g/L) were investigated at variable time (10, 20,
30,….90min) using 50 ml of varying conc. of metal ions (50, 100, 150, 200, 250 and 300 mg/L)
in 250 ml beaker at 303K and stirring speed of 240 rpm, equilibrium time was investigated for
the adsorption of metal ions on each adsorbent. Equilibrium‘ concentrations of metal ions were
investigated by analyzing the filtrate after the adsorption experiment at time interval of 10
minutes using atomic absorption spectrophotometer (Perkin Elmer AAnalyst 700).Adsorption
capacity and percent adsorption of metal ions were calculated by using the equation (3.1) and
(3.3).
3.5.2 Effect of „Adsorbent Dose‟ on Adsorption‟ of (Pb2+
)
The variable ‗adsorbent dose was employed in the range of 1-5gL-1
in 50 ml of 250 mgL-1
solution of Pb2+
with stirring speed of 240 rpm in a 250ml beaker for equilibrium time. the
residual concentration of metal ions were analyzed after solid-liquid separation by using atomic
absorption Spectrophotometer. Uptake capacity and percent removal of metal ions were
calculated by using the equation (3.1) and (3.3)
46
3.5.3 Effect of ‗pH‘ on Adsorption of Metal Ions on Adsorbent
50 ml solution (250 mg/L, Pb2+
) was taken in 250 ml beaker with the addition of 2g/L of
the adsorbent. This combination was agitated at speed of 240 rpm for equilibrium time over a pH
range of 3-6 (3, 4, 5, 6). HCl (0.1M) and NaOH (0.1M) solutions were employed for pH
adjustment. The residual metal ions concentration, uptake capacity and %adsorption of metal cat-
ions were determined.
3.5.4 Effect of ‗Temperature‘ on Adsorption ofPb
2+ on Adsorbent
To investigate the temperature effect the adsorption process was conducted in the
temperature range‗303-343K‘. The other experimental conditions were: Initial metal ions
concentrations = 250 mg/L, equilibrium time, stirring speed = 240 rpm, pH = 6 and adsorbent
dose = 2g/L. At the end of each experiment, liquid was separated from solid and the residual
metal ions concentration, adsorption capacity and %adsorption of metal ions were calculated.
3.6 Characterization
3.6.1 UV–Visible Spectrophotometric Analysis
UV–Vis. spectrophotometer (Perkin Elmer Lambda 25), was used to analyze the residual
dye concentrations after the separation of liquid from the solid. The instrument was standardized
with doubly de-ionized water to adjust the zero absorbance before sample analysis at λmax for the
corresponding dye. The wavelengths (λmax) correspond to maximum absorbance of the OG and
TY dye samples were chosen as 476 nm and 405 nm respectively. The residual concentrations of
OG and TY dyes were determined by using standard calibration curve or by using Beer Lambert
law.
3.6.2 Flame Atomic Absorption Spectroscopy „FAAS‟
FAAS ―Perkin Elmer AAnalyst 700‖was employed to investigate the residual metal
concentration. For this purpose after the completion of each experiment, the liquid and solids
were separated from each other through centrifugation, at 2500 rpm in 10 min. The supernatants
were thereafter filtered through whatman 41 filter paper and were used for analysis of
47
Pb(II)concentration. Standards of different conc. were made using 1000mg/L of Pb(II) standard
solution to obtain the standard calibration curve.
3.6.3 Scanning Electron Microscopy „SEM‟
Exterior structure of the prepared adsorbent was inspected through ‗SEM‘ ―JSM-6490,
JEOL‖. For this determination, the sample powder was scattered on conducting carbon-tap which
was stuck on aluminum-stub. It was transferred to vacuum compartment of sputter ―JFC- 1600,
JEOL‖ and covered with gold. It was then placed in the sample examination chamber of the
SEM. The micrographs were documented at the increasing voltage of fifteen KV and working
compartment of the scanning electron microscope and the images were documented at
accelerating voltage of 15 KV and working space of ten millimeters. Elemental investigation of
the adsorbents was carried with EDX analyzer ―Oxford, Inca-200‖.
3.6.4 X-ray Diffractometry „XRD‟
The prepared adsorbents were analyzed with X ray diffractometer ―XRD, JEOL JDX-
3532‖by Cu-Kα rays. Diffractometer was run through forty kV voltage and twenty miliampere
current. Scanning of the samples were completed in the 2θ range 2−80 °, at a step angle equal to
0.05 °and the scanning speed of 0.1° sec-1. Composition of crystalline entities was known with
the help of standard software ‗JDX-3500‘.
3.6.5 Fourier Transform Infrared Spectrometry „FT-IR‟
All the desired samples analyzed by IR spectroscopy using FTIR spectrometer
―Schimadzue, IR-Prestige-21, FTIR-8400S‖ in the wavenumber range of 400-4000 cm-1
. The
samples were subjected to sample compartment for scanning.
48
RESULTS AND DISCUSSION CHAPTER # 4
4.1 UV,-Visible Spectroscopy of Representative Samples
Analysis of the residual dye concentrations of the desired samples are shown in the figures
4.1 and 4.2. The former indicated that the absorbance peaks of the of the residual dye
concentrations adsorbed on the surface of KOH modified ‗Rice Husk Char
‘ (KMRHC) and KOH
modified ‗Rice Husk Ash
‘ (KMRHA) are very low which presented that adsorption of Orange, G
dye on the surfaces of KMRHC and KMRHA is high as compare to the other two adsorbents.
This indicated that KOH modification of RHC and RHA enhanced their adsorption capabilities.
Almost the same results for adsorption of Titan Yellow dye on identical adsorbents were also
investigated (Fig. 4.2). However, slight differences in the absorbance peaks revealed that the
nature of adsorbate changes which resulted in the variation of the absorbance peaks for
adsorption of OG and TY dyes on the same materials. It suggested that nature of adsorbate could
also affect the adsorption process.
4.2 Scanning Electron Microscope (SEM) Studies
SEM study is employed to examine the exterior structure of adsorbents. The pores present in
the adsorbent can be divided into macropores, transitional pores and micropores. The effective
radius of pores greater than 500- 1000 Å are termed as macropores which have surface area
between 0.5 and 2.0 m2 /g. The radius of transitional pores falls within 40-200 Å with surface
area between 20-70 m2 /g. Micropores have radius usually less than 20 Å which almost provides
95 % of the total surface area (Muthukumaran & Beulah, 2010).
SEM pictures of RHC before and after adsorption indicated in figure 4.3. The picture in
Figure 4.3A indicated irregular pores of different dimensions. The change in the surface
morphology has been inspected after adsorption of (OG) dye on the adsorbent (Fig. 4.3B).
However, some pores of the adsorbent are not completely deposited by the dye molecules which
indicated that the adsorbent don‘t possess too much active sites for the adsorbate molecules. On
the other hand KOH modification of RHC indicated that the surface of adsorbent became highly
porous (Fig. 4.4A) with enhanced surface active sites. The adsorption capability of the modified
Rice Husk Char is very high for the dye (OG) as indicated in Figure 4.4B. After loading of the
49
OG dye, a smooth appearance in surface morphology has been inspected (Fig. 4.4B). The
adsorption of Pb2+
on the surface of KMRHC is shown in the Figure 4.5 which indicated
morphological change in the surface of adsorbent. The porous surface of the particles shown in
the Figure 4.4A is completely changed by the accumulation of the Pb2+
ions.
SEM micrograph of RHA before and after adsorption is shown in the figure 4.6. The
irregular porosity in the surface of RHA (Fig. 4.6A) is completely changed after the adsorption
of Pb2+
(Fig. 4.6B). Furthermore, the growth in particle size of adsorbent after adsorption of Pb2+
indicated that Pb2+
have been accumulated on its surface. KOH modification of the RHA
increased the porosity of adsorbent with foam like appearance and particle size ranging from
nano meter to micro meter (Fig. 4.7A). The small particle size inferred for large surface area
which enhanced the adsorption efficiency of the adsorbent. After adsorption of Pb2+
, its surface
morphology is completely changed with smooth appearance and complete deposition of the
Pb2+
ions (Fig. 4.7B).
50
200 400 600 800
0
1
2
3
4
5
6
Ab
so
rba
nce
Wavelength (nm)
bc
de
a
Figure, 4.1 UV-
,Visible Spectra for (A) Original OG Dye Solution (80mg/L),
(B) Residual Dye Conc. after Adsorption on RHA, (C) Residual Dye Conc. after
Adsorption on RHC, (D) Residual Dye Conc. after The Adsorption on KMRHA, (E)
Residual Dye Conc. after the Adsorption on KMRHC.
51
200 400 600 800
0
1
2
3
4
5
Ab
so
rba
nce
Wavelength (nm)
a
bcd
e
Figure, 4.2 UV Visible Spectra, for (A) Original TY Dye Solution (80mg/L) (B)
Residual Dye Conc. after Adsorption on RHA (C) Residual Dye Conc. after Adsorption
on RHC(D) Residual Dye Conc. after the Adsorption on KMRHA (E) Residual Dye
Conc. after the Adsorption on KMRHC.
52
Figure 4.3 „Scanning Electron Micrograph
‘ ―SEM‖ of, (A) Rice Husk Char,
(B) Orange G Dye Loaded Rice Husk Ash.
A
A
B
53
Figure 4.4 „Scanning Electron Micrograph
‘ ―SEM‖ of, (A) KOH Modified
Rice Husk Char, (B) Orange G Dye Loaded KOH Modified Rice Husk Char.
A
A
B
54
Figure, 4.5
„Scanning Electron Micrograph
‘ ―SEM‖ of
, Pb Loaded KOH
Modified Rice Husk Char.
55
Figure 4.6 „Scanning Electron Micrograph‘ ―SEM‖ of (A) RHA, (B) Pb Loaded RHA
A
B
56
Figure 4.7 „Scanning Electron Micrograph
‘ ―SEM‖ of
, (A) KMRHA, (B) Pb Loaded
KMRHA.
A
A
B
57
4.3 „Energy Dispersive X-Ray
‟ „EDX‟ Analysis
‗EDX‘ analysis (Fig. 4.8A) indicated that the adsorbent, Rice Husk Char before adsorption
contained various elements, i.e. Si, O, C, Al, Mg, Ca, p and K in different quantities. After the
adsorption of Titan Yellow dye on the RHC, it contained Sulfur and Nitrogen in addition to these
elements, moreover the intensities of C and O peaks are enhanced (Fig. 4.8B) which revealed the
confirmation of dye adsorption on the surface of adsorbent. Titan Yellow dye is an organic dye
which consists of C, H, O, N and S. Hence Figure 4.8B inferred for the confirmation of
adsorption dye on adsorbent.
‗EDX
‘ analysis (Fig. 4.9A) showed that Rice Husk Ash enclosed several elements, i.e‘ Si, O,
Al, Mg, Fe, P and K in diverse quantities. Presence of maximum of the mentioned elements
within ‗RHA‘ was too stated by other investigators (Estevez, et al, 2009 & Kulak, et al, 2008).
After the adsorption of Pb2+
on the RHA, a sharp peaks Pb was also found in the EDX spectrum
along with the other elements (Fig. 4.9B) which reveals that the adsorbent has affinity for metal
ions.
The KOH modified Rice Husk Char (KMRHC) contained different elements, i.e. Si, O, C,
Al, Mg, p and K in different quantities as indicated in the EDX spectrum (Fig. 4.10A). After the
adsorption of Titan Yellow dye on the KMRHC, it contained S and N in addition to other
elements, moreover the enhancement of intensities of C and O (Fig. 4.10B) revealed that the TY
dye (organic dye) has been adsorbed on the surface of adsorbent. Fig. 4.10C indicated that
adsorbent ‗KMRHC‘ could also have a very strong affinity to adsorb heavy metals as confirmed
by the sharp peak of Pb in the EDX spectrum.
EDX analysis (Fig. 4.11A) inferred that KOH modified Rice Husk Ash (KMRHA) contained
different elements, i.e. Si, O, Al, Mg, p and K in variable amounts. After the adsorption of Titan
Yellow dye on the KMRHA, it contained S and N along with these elements; the enhanced
intensities of C and O peaks (Fig. 4.11B) confirmed that dye has been loaded to adsorbent. The
adsorbent KMRHA could have also strong affinity to adsorb heavy metals which was confirmed
by the sharp peak of Pb in the EDX spectrum (Fig. 4.11C).
58
Figure‟ 4.8 „Energy Dispersive X-Ray
‘ (EDX) Analysis Spectra of (A) RHC, (B) TY
Dye Loaded RHA
59
Figure‟ 4.9 „Energy Dispersive X-Ray
‘ Analysis Spectra of (
‗A
‘) RHA, (
‗B
‘) Pb
Loaded RHA
60
Figure‘ 4.10
„Energy Dispersive X-Ray
‘ Analysis Spectra of (A) KMRHC, (B)
TY Dye Loaded KMRHC, (C) Pb Loaded KMRHC.
61
Figure‟ 4.11 „Energy Dispersive X-Ray
‘ Analysis Spectra of (A) KMRHA, (B) TY Dye
Loaded KMRHA, (C) Pb Loaded KMRHA.
62
4.4 ‗X-Ray Diffraction‘ „XRD‟ Analysis
The crystallinity of synthesized products and its phase compositions could be identified
using XRD technique. Figure 4.12A indicated that Rice Husk Char (RHC) almost consists of
amorphous of Silica (SiO2) as indicated in the EDX Fig. 4.8A. However, due to thermo-chemical
treatment transformed some peaks of crystalline materials were appeared i.e. Al2O3, K2O2,
3K2O.SiO2, SiO2 (quartz), SiO2 (stishovite) (XRD, Fig. 4.12B) while the rest of the matter is
amorphous silica (EDX Fig. 4.8B). This revealed that KOH modification of RHC had
significantly influenced the amorphous nature and phase composition of the adsorbent. The
presence of the crystalline oxides of metals and non-metals in the backbone of amorphous matter
has significantly affected the surface morphology of the adsorbents (SEM, Fig. 4.3A and 4.4A)
which indicated variable changes in the porosity of the two adsorbents. KOH modification of
RHA has also converted some of the amorphous matter into crystalline one i.e. 3K2O.SiO2and
traces of crystalline silica (Cristobalite) (XRD, Fig. 4.13B). The presence of crystalline particles
in the amorphous matter has changed the surface morphology and particle size of the adsorbents
(SEM, Fig. 4.6A and 4.7A).
63
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
0
200
400
600
800
1000
1200
1400
Inte
nsity (
a.u
.)
2(degree)
A. RHC
B. KMRHC
a, 3K2O.SiO
2
b, K2O
2
c, Al2O
3
d, SiO2 (Quartz)
e, SiO2 (Stishovite)
A
B
a
b
a
a
c
dd
ba
e
Figure‘ 4.12 XRD Pattern of (A) RHC, (B) KMRHC.
64
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
Inte
nsity (
a.u
.)
2(degree)
A, RHA
B, KMRHA
a, 3K2O.SiO
2
b, SiO2 (Quartz)
c, SiO2 (Cristobalite)
d, SiO2 (stishovite)
a
a
b
b
c
d
B
A
Figure‘ 4.13 XRD Pattern of (A) RHA, (B) KMRHA.
65
4.5 FT-IR Spectral Analysis
IR analysis provides information about the structure and functional groups carried by
adsorbents. Fig. 4.14 (a, b, c and d) indicated IR spectra of Rice Husk Char (RHC), Pb, TY and
OG Loaded on RHC respectively. The functional groups in adsorbent as well as its porous nature
are accountable for its adsorption properties. IR accessible groups (Fig 4.14a) indicated the
complex nature of RHC. The broad peak between 3000- 3700 cm-1
is because of the H-OH & Si-
OH stretching vibrations (Nakbanopote, et al., 2007; Adam, et al., 2009) the absorption peak at
1614.2 is due to OH bending, that at 1058.3 is due to Si-O-Si, asymmetric stretching, C-O
stretching and peaks at 440 and 794.8 cm-1
are due to Si-O symmetric stretching, (Battisha, et
al., 2001; Dahlan, et al., 2008; Banerjee, et al., 2016). The shifting of peaks from 440.1cm-1
to
440.5cm-1
, 794.8cm-1
to 790.9cm-1
, 1058.3cm-1
to 1055.09cm-1
and 1614.2cm-1
to 1600cm-1
(Fig. 4.14a& 4.14b) indicates the binding Pb(II) ions with Si-O and –OH groups (Sheng, et
al.,2004). Along with the shifting of different peaks, the additional peaks at 1245 and 1926 cm-1
(Fig. 4.14c) and at 1243cm-1
and 2856 cm-1
(Fig. 4.14d) were inspected. The absorption peaks at
1234 and 1245 are due to C=C aromatic bending and that at 2856 and 2926 cm-1
are because of
C-H bending vibrations, (Sheng, et al.2004).
Figure 4.15 ascribed the FTIR, spectra of KMRHC and loaded KMRHC. The shifting of
absorption peaks from 427.5 cm-1
to 439.6cm-1
, 772cm-1
to 776cm-1
, 1032.5cm-1
to 1064.7cm-1
and 3238.2cm-1
t0 3228.1cm-1
inferred for the interaction of metal cat-ions with Si-O and OH
groups of the adsorbent. The peak at 1366cm-1
(Fig. 4.15a) which was due to the OH plane
bending disappeared (Fig. 4.15b) on the interaction to Pb(II) ions (Sheng, et al.,2005). This
showed that binding of Pb(II) with Si-O and OH groups could disturb the plane of bending
vibration of the OH group. Moreover the bending vibration of Si-OH was detected at 962cm-1
(Fig. 4.15b) (Poh, et al., 2006). The absorption peak of OH plane bending at 1366cm-1
(Fig.
4.1.15a) was also disappeared by the interaction of TY and OG dyes (Fig 4.15c and 4.15d). The
absorption peaks at 1256.3cm-1
and 2934.1cm-1
(Fig 4.15c) were attributed to C=C aromatic
bending and C-H bending which confirms the adsorption of organic dyes on the adsorbent. The
same modes of vibration could also be detected at 1252 cm-1
and 2863.01 cm-1
(Fig. 4.15d). The
shifting of peaks at different positions indicated that the chemical nature of adsorbates (TY &
OG dyes) is different from each other.
66
The IR spectra of RHA and Pb, TY and OG loaded RHA are given in the figure 4.16. The
intense peak at 450.8 cm-1
is because of the bending vibration of Si-O-Si, absorption bands at
796.6 cm-1
& 1058.5 cm-1
are attributed to symmetric and asymmetric stretching of Si-O-Si (Fig.
4.16a) (Poh, et al., 2006). This indicates that SiO2 is the major component of Rice Husk Ash.
Shifting of the peaks has been inspected in the spectra which indicated the interaction of Pb and
dye particles with the adsorbent. Furthermore, additional absorption bands at 1246.03 & 2926.06
(Fig 4.16c) and at 1242 & 2856.03 (Fig 4.16d) were inspected which attribute to C=C aromatic
bending and C-H bending. KOH modification of the RHA leads to the shifting of adsorption
bands from 450.8cm-1
to 447.2cm-1
, 796.6cm-1
to793.7cm-1
and 1058.5cm-1
to 1059.9cm-1
(Fig
4.16a and 4.17a). Shifting of absorption bands and additional peaks are inspected in the IR
spectra of KMRHA on loading with Pb and dye particles (Fig. 4.17) which revealed for the
binding of Pb and dye particles with the active sites of the adsorbent.
67
4000 3000 2000 1000 0
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
1614.2
1600
3000-3700
3000-3700
3000-3700
Tra
nsm
itta
nce
(a
.u)
Wavenumber cm-1
a. RHC
b. Pb on RHC
c. TY on RHC
d. OG on RHC
a
b
c
d
1058.34
794.8
440.1
440.5
1055.09
790.9
1965.4
438.5
796.5
1063.9
1603.21965.4
448.0
795.8
1059.1
1965.4
2189.8
2926.0
2856.1
1245.0
1243.05
3000-3700
Figure 4.14 FTIR Spectra of: (A) RHC, (A) Pb Loaded RHC, (C) TY Loaded
RHC and (D) OG Load RHC
68
4500 4000 3500 3000 2500 2000 1500 1000 500 0
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
962
Tra
nsm
itta
nce
(a
. u
)
Wavenumber cm-1
a. KMRHC
b. Pb on KMRHC
c. TY on KMRHC
d. OG on KMRHC
a
b
c
d
1047.2
778.5
436.1
1965.53350.7 414.6
1061.4
3261.3
1064.7
439.6
1965.53228.1
3238.2
1032.5
427.5
1252.0
1256.32934.1
2863.01
1366
772
1507
962776
776.5
Figure 4.15 FTIR Spectra of: (A) KMRHC, (B) Pb Loaded KMRHC, (C) TY Loaded
KMRHC and (D) OG Load KMRHC
69
4000 3000 2000 1000 0
50
100
150
200
250
300
350
400
450
Tra
nsm
itta
nce
(a
. u
)
Wavenumber (cm-1)
a. RHA
b. Pb on RHA
c. TY on RHA
d. OG on RHA
450.8
796.6
1058.5
1060.09
796.86
450.99
1965.6
1068.4
795.9
452.08
448.49
797.4
1063.5
a
b
c
d
1965.5
2856.03
1242
1246.031966.012962.06
566
Figure 4.16 FTIR Spectra of: (A) RHA, (B) Pb Loaded RHA, (C) TY Loaded RHA
and (S) OG Load RHA
70
4000 3000 2000 1000 0
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420T
ran
sm
itta
nce
(a
. u
)
Wavenumber cm-1
a. KMRHA
b. Pb on KMRHA
c. TY on KMRHA
d. OG on KMRHAa
b
c
d 1063.4
793.7
449.9
1059.9
793.7
447.2
1965.46
1965.41
1966.3
1064.2452.6
794.9
1049.8
794.6
451.0
1239.2
1240.5
2934.3
2855.4
Figure 4.17 FTIR Spectra of: (A) KMRHA, (B) Pb Loaded KMRHA, (C) TY Loaded
KMRHA and (D) OG Load KMRHA
71
4.6 Effect of Temperature on the Activation of RHC, KMRHC, RHA and KMRHA
The activated ‗Rice Husk Char‘ and KOH Modified ‗Rice Husk Char‘ were prepared at
different temperatures [300◦C, 350
◦C, 400
◦C, 450
◦C and 500
◦C] and employed for adsorption of
‗Orange G
‘ dye. Results of this study were given in the tables‘ 4.1 & 4.2 and Figure‘ 4.18 which
indicated that adsorption efficiency of the RHC was improved with elevation in temperature
from 300◦C to 400
◦C and thereafter remained constant and that of KMRHC was increased with
the increase in temperature from 300◦C to 450
◦C and further increase in the activation
temperature have no significant effect on the adsorption of dye. Hence further
preparation/activation of RHC and KMRHC was brought out at 400◦C and 450
◦C respectively.
Activation of‗ RHA and KMRHA‘ was completed at varying temperatures [600◦C, 650
◦C,
700◦C,750
◦C, and 800
◦C] and employed for the ‗adsorption of OG dye‘. Experimental results of
this study were listed in the tables 4.3 & 4.4 and Figure 4.19 which revealed that activation of
both the RHA and KMRHA increased with temperature and optimized at 700◦C and 750
◦C
respectively.
Table 4.1 Effect of ‗Temperature
‘ on the Activation of RHC‘
Temperature
(oC)
Absorbance of
the filtrate
Concentration
of the filtrate
Ce (mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
300 0.771 42.8 18.6 46.5
350 0.648 36.0 22.0 55.0
400 0.518 28.8 25.6 64.0
450 0.513 28.5 25.7 64.3
72
Table 4.2 Effect of ‗Temperature
‘ on the Activation of KMRHC‘
Temperature
(oC)
Absorbance of
the filtrate
Concentration of
the filtrate
Ce(mg/L)
Dye
adsorbed
qe(mg/g)
% Dye
adsorbed
300 0.284 15.8 32.1 80.2
350 0.149 8.3 35.8 89.6
400 0.091 5.1 37.4 93.6
450 0.057 3.2 38.4 96.0
500 0.054 3.0 38.5 96.2
Table 4.3 Effect of ‗Temperature
‘ on the Activation of RHA‘
Temperature(oC)
Absorbance of
the filtrate
Concentration
of the filtrate
Ce(mg/L)
Dye adsorbed
qe(mg/g)
% Dye
adsorbed
600 0.876 48.7 15.6 39.1
650 0.705 39.2 20.4 51.0
700 0.610 33.9 23.05 57.6
750 0.603 33.5 23.25 58.1
73
Table 4.4 Effect of ‗Temperature
‘ on the Activation of KMRHA‘
Temperature
(oC)
Absorbance of
the filtrate
Concentration
of the filtrate
Ce(mg/L)
Dye adsorbed
qe(mg/g)
% Dye
adsorbed
600 0.516 28.7 25.6 64.1
650 0.334 18.6 30.7 76.7
700 0.214 11.9 34.05 85.1
750 0.127 7.1 36.4 91.1
800 0.124 6.9 36.5 91.3
Figure 4.18 „Effect of Temperature
‘ on the Activation of RHC & KMRHC.
40
50
60
70
80
90
100
250 300 350 400 450 500 550
% D
ye a
dso
rbe
d
Temperature (oC)
Temperature effect on the activation of adsorbents
RHC
KMRHC
74
Figure 4.19 „Effect of Temperature
‘ on Activation of RHA & KMRHA.
4.7 Adsorption of Orange G (OG) Dye on RHC, KMRHC, RHA and KMRHA
4.7.1 „Effect of
„Contact Time on „Adsorption of OG on RHC, KMRHC, RHA and
KMRHA
Adsorption experiment was run in the time range of 10-90min with the interval of 10
minutes to investigate the effect of stirring time on the adsorption of OG dye on adsorbents. The
equilibrium was established after 80 minutes for RHC, 60 min for KMRHC &RHA and 70 min‘
for KMRHA. The adsorption process was brought out on the original dye conc. equal to 80 mg/L
containing 2gL-1
of the adsorbent dose at pH = 4 with agitation speed of 240 rpm and
temperature of 303K. Experimental results of the adsorption are depicted in the Figures 4.21,
4.22 and tables 4.5, 4.6, 4.7 and 4.8 which indicated that the adsorption capacity (mg/g) of OG
on KMRHC increases in the first 50-60 minutes and then remained constant. At the beginning,
the availability of more active sites of the adsorbents and high concentration of OG increased the
adsorption rate. After 60 min stirring time the availability of surface active sites decreased and
also the dye concentration is reached to its minimum which didn‘t change the adsorption
30
40
50
60
70
80
90
100
550 600 650 700 750 800 850
% D
ye a
dso
rbe
d
Temperature (oC)
'Temperature effect on activation of adsorbents'
RHA
KMRHA
75
capacity significantly. The adsorption capacity (mg/g) of OG on RHC, KMRHC, RHA and
KMRHA was investigated as 26, 38.4, 23.05and 36.45mgg-1
respectivelyonequilibrium stirring
time. The percentage adsorption of OG on RHC, KMRHC, RHA and KMRHA was observed as
65.1%, 96%, 57.6% and 91.1% respectively at equilibrium. Results of the adsorption study
indicated that the uptake capacity (mg/g) and percent adsorption of OG dye on KMRHC and
KMRHA is significantly high as compare to the corresponding RHC and RHA which suggested
that the KOH modification of RHC and RHA enable them efficient adsorbents by making these
adsorbents highly porous with enhanced active sites for removal of OG from aqueous media.
Figure‟ 4.20 Effect of Agitation Time on Percent Adsorption of OG on RHC, KMRHC,
RHA and KMRHA from Aqueous Media, Experimental Conditions were: pH = 4, T =
303K, Adsorbent Concentration = 2g/L, C0= 80 mg/L
0
5
10
15
20
25
30
35
40
10 20 3040
5060
Up
take
cap
acit
y (m
g/g)
Time (min)
RHC
KMRHC
RHA
KMRHA
76
Figure‟ 4.21 Effect of stirring Time on Uptake Capacity (mg/g) of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media, Experimental Conditions were: pH=
4, T = 303K, Adsorbent Concentration = 2g/L, C0= 80 mg/L
0
20
40
60
80
100
120
0 20 40 60 80
% O
G A
dso
rpti
on
Time (min)
RHC
KMRHC
RHA
KMRHA
77
Table 4.5 Time Optimization Study for ‗Adsorption of OG‘ on Rice Husk Char. Co=
80 Mg/L, pH = 4, Temp = 303K Adsorbent Dose = 2g/L
S. No. Stirring
Time (min)
Absorbance
of filtrate
Conc. of
filtrate Ce
(mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
1 10 1.087 60.4 9.8 24.5
2 20 0.869 48.3 15.8 39.6
3 30 0.703 39.1 20.4 51.1
4 40 0.604 33.6 23.2 58.0
5 50 0.531 29.5 25.2 63.1
6 60 0.518 28.8 25.6 64.0
7 70 0.507 28.2 25.9 64.7
8 80 0.502 27.9 26.0 65.1
9 90 0.502 27.9 26.0 65.1
78
Table 4.6 Time Optimization Study for Adsorption‘ of OG on KOH Modified Rice
Husk Char. Co= 80 mg/L, pH= 4, Temp = 303K Adsorbent Dose = 2g/L, Volume of Dye
Solution = 50ml
S. No Stirring
Time (min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye adsorbed
qt (mg/g)
% Dye
adsorbed
1 10 0.531 29.5 25.2 63.1
2 20 0.378 21.0 29.5 73.7
3 30 0.217 12.1 33.9 84.8
4 40 0.118 6.6 36.7 91.7
5 50 0.0738 4.1 37.9 94.8
6 60 0.057 3.2(Ce) 38.4 (qe) 96.0
7 70 0.057 3.2(Ce) 38.4 (qe) 96.0
79
Table 4.7 Time Optimization Study for ‗Adsorption of OG
‘ on Rice Husk Ash. Co=
80 mg/L, pH = 4, Temp = 303K, Adsorbent Dose = 2g/L
S. No. Stirring
Time (min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
1 10 0.869 48.3 15.8 39.6
2 20 0.732 40.7 19.6 49.1
3 30 0.689 38.3 20.8 52.1
4 40 0.649 36.1 21.9 54.8
5 50 0.621 34.5 22.7 56.8
6 60 0.610 33.9(Ce) 23.05 (qe) 57.6
7 70 0.610 33.9(Ce) 23.05 (qe) 57.6
80
Table 4.8 Time Optimization Study for Adsorption‘ of OG Dye on KOH Modified
Rice Husk Char. Co= 80 mg/L, pH= 4, Temp = 303K Adsorbent Dose = 2g/L.
S. No Stirring
Time (min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
1 10 0.477 26.5 26.75 66.8
2 20 0.390 21.7 29.15 72.8
3 30 0.307 17.1 31.45 78.6
4 40 0.262 14.6 32.7 81.7
5 50 0.181 10.1 34.95 87.3
6 60 0.149 8.3 35.85 89.6
7 70 0.127 7.1(Ce) 36.45(qe) 91.1
8 80 0.127 7.1(Ce) 36.45 (qe) 91.1
81
4.7.2 Effect of „Adsorbent Dose‟ on Adsorption of OG on RHC, KMRHC, RHA and
KMRHA
Variable adsorbent dose in the range of 1−5 g/L was applied to 50 ml of 80 mg/L of dye
solution at 303 K and pH = 4 to study the adsorption properties of the adsorbents. Results of this
study were listed in figures 4.22, 4.23 and tables 4.9, 4.10, 4.11 and 4.12 which indicated that
adsorption capacity (mg/g‘) was decreased with the increase in adsorbent dose. The highest
adsorption capacity (mg/g) for OG was investigated as 33.9, 52.0, 26.9 and 46.0 mg/g on 1g/L of
the RHC, KMRHC, RHA and KMRHA respectively. This indicated that for limited surface
active sites, the available concentration of dye is high which increase the uptake capacity ‗mg/g‘.
However, % adsorption of the dye is decreased at low value of adsorbent does. The percentage
adsorption of the OG was increased at high mass of adsorbent because of the availability of more
active sites for the definite number of dye molecules (Kulkarni, et al., 2012). The percentage
removal of OG reached to highest at 5g/L of the adsorbent dose. Further increase in the
adsorbent concentration have no effect on the percent removal of OG dye, which inferred for
maximum adsorption of OG dye and minimum level of dye‘s concentration in aqueous media
(Nomanbhay, et al., 2005). It has been inspected that the KOH modified adsorbents (KMRHC &
KMRHA) could remove the OG dye from aqueous media almost completely at adsorbent dose of
5g/L.
82
Figure 4.22 Effect of ‗Adsorbent Dose
‘ on the Uptake Capacity (mg/g) of OG
on RHC, KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 4, T = 303K, C0= 80 mg/L
0
10
20
30
40
50
60
12
34
5
Up
take
Cap
acit
y (m
g/g)
Adsorbent dose (g/L)
OG
RHC
KMRHC
RHA
KMRHA
83
Figure 4.23 Effect of ‗Adsorbent Dose‘ on the %age Removal of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions: pH =
4, T = 303K, C0= 80 Mg/L
0
20
40
60
80
100
120
0 1 2 3 4 5 6
% O
G a
dso
rpti
on
Adsorbent dose (g/L)
RHC
KMRHC
RHA
KMRHA
84
Table 4.9 Adsorbent Dose Optimization Study for Adsorption of Orange G Dye on
Rice Husk Char. Co= 80 mg/L, Initial pH = 4, Temp = 303K, Agitation Time =80min.
Table 4.10 Weight Optimization Study for the ‗Adsorption, of OG
‘ on KOH Modified
Rice Husk Char. Co= 80 mg/L, pH= 4, Temp = 303K Contact Time = 60mins.
S. No. Adsorbent
dose (g/L).
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.829 46.1 33.9 42.3
(2) 2 0.502 27.9 26.0 65.1
(3) 3 0.390 21.7 19.4 72.8
(4) 4 0.329 18.3 15.4 77.1
(5) 5 0.300 16.7 12.6 79.1
S. No. Adsorbent
dose (g/L).
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.504 28 52 65
(2) 2 0.057 3.2 38.4 96.0
(3) 3 0.050 2.8 25.7 96.5
(4)
4 0.045 2.5 19.3 96.8
(5) 5 0.041 2.3 15.5 97.1
85
Table 4.11 Adsorbent Dose Optimization Study for Adsorption of OG on
RHA, Co= 80 mg/L, Initial pH = 4, Temp = 303K, Agitation Time=80min
Table 4.12 Weight Optimization Study for ‗Adsorption of OG‘ on KMRHA,
Co= 80 mg/L, pH = 4, Temp = 303K, Contact Time = 70mins, Volume of Dye Solution
= 50ml
S. No. Adsorbent
dose (g/L).
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.955 53.1 26.9 33.6
(2) 2 0.610 33.9 23.05 57.6
(3) 3 0.498 27.7 17.43 65.3
(4) 4 0.383 21.3 14.67 73.3
(5) 5 0.354 19.7 12.06 75.3
S. No. Adsorbent
dose (g/L).
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.612 34 46.0 57.5
(2) 2 0.127 7.1 36.45 91.1
(3) 3 0.081 4.5 25.16 94.3
(4) 4 0.055 3.1 19.02 96.1
(5) 5 0.052 2.9 15.45 96.3
86
4.7.3 Effect of „Dye Concentration
‟ on Adsorption of OG on RHC, KMRHC, RHA and
KMRHA
The adsorption of ‗OG‘ on RHC, KMRHC, RHA and KMRHA was investigated at the
initial conc. ranging from 20-120 mg/L (20. 40, 60, 80,100, 120). The adsorption experiment was
performed at 303K and pH 4 for equilibrium stirring time and 2g/L of adsorbent dose. Results of
this process are shown in the figures, 4.24, 4.25 and tables 4.13, 4.14, 4.15and 4.16 which
indicated that the dye uptake capacity on the adsorbents was high at high initial conc. of dye. The
maximum adsorption capacity of OG on RHC, KMRHC, RHA and KMRHA was investigated as
28.9, 51.5, 27.9 and 48.5 mg/g, at initial dye conc. of 120 mg/L. The high adsorption capacity
(mg/g) on the surface of adsorbents at high initial concentration of the dye solution is attributed
to multilayer formation. This is confirmed by the high value of correlation factor in the
Freundlich adsorption isotherm (Table 4.27).
The percentage adsorption of OG from aqueous media on the adsorbents was investigated
to be decreased as the initial conc. of dye was increased. For low dye concentration, the active
sites of the adsorbents are greater which completely remove the dye molecules and hence the
percent adsorption of dye increases. However, at elevated dye conc., the active sites of adsorbent
become fewer which are not enough to completely remove the OG molecules from aqueous
media, hence decrease in the percentage adsorption of OG from aqueous media was inspected.
The maximum percentage removals of OG dye on RHC, KMRHC, RHA and KMRHA was
investigated as 88%, 98%, 85.5% and 95.5% at 20 mg/L of the initial dyes concentrations. It
revealed for the efficiency of KOH-modified adsorbents.
87
Figure 4.24 „Effect of Initial Dye Concentration
‘ on the Uptake Capacity, of
OG on RHC, KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 4, T = 303K, Adsorbent Concentration = 2g/L,
0
10
20
30
40
50
60
20 40 60 80100
120
qe
(m
g/g)
Concentration (mg/L)
OG
RHC
KMRHC
RHA
KMRHA
88
Figure 4.25 „Effect of Initial Dye Concentration
‘ on %
‗Adsorption
‘ of OG on
RHC, KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 4, T = 303K, Adsorbent Concentration = 2g/L,
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140
% O
G A
dso
rpti
on
Concentration (mg/L)
RHC
KMRHC
RHA
KMRHA
89
Table 4.13 Concentration Optimization Study for Adsorption of Orange G Dye on Rice Husk
Char. Adsorbent Dose = 2g/L, pH= 4, Temp = 303K.
S. No
Dye
conc.
(mg/L)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe
(mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.043 2.4 8.8 0.380 0.944 0.272 88
2 40 0.149 8.3 15.8 0.919 1.198 0.525 79.2
3 60 0.284 15.8 22.1 1.198 1.344 0.714 73.6
4 80 0.502 27.9 26.0 1.445 1.414 1.073 65.1
5 100 0.790 43.9 28.0 1.642 1.447 1.567 56.1
6 120 1.119 62.2 28.9 1.796 1.460 2.152 48.1
90
Table 4.14 Concentration Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Char. Adsorbent Dose = 2g/L pH = 4, Temp = 303K.
S. No
Dye
conc.
(mg/L)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.007 0.4 9.8 -0.396 0.991 0.040 98.0
2 40 0.021 1.2 19.4 0.079 1.287 0.061 97.0
3 60 0.036 2.0 29.0 0.301 1.462 0.068 96.6
4 80 0.057 3.2 38.4 0.505 1.584 0.083 96.0
5 100 0.120 6.7 46.6 0.826 1.668 0.143 93.3
6 120 0.214 16.9 51.5 1.227 1.712 0.328 85.9
91
Table 4.15 Concentration Optimization Study for Adsorption of Orange G Dye on Rice Husk
Ash, Adsorbent Dose = 2g/L, pH. = 4, Temp. = 303K, stirring Time. =60min.
S. No
Dye
conc.
(mg/L)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.052 2.9 8.55 0.462 0.931 0.339 85.5
2 40 0.221 12.3 13.85 1.089 1.141 0.888 69.25
3 60 0.392 21.8 19.1 1.338 1.281 1.141 63.6
4 80 0.610 33.9 23.05 1.530 1.362 1.470 57.6
5 100 0.853 47.9 26.05 1.680 1.415 1.835 52.1
6 120 1.245 64.2 27.9 1.807 1.807 2.301 46.5
92
Table 4.16 Concentration Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Ash. Adsorbent Dose = 2g/L pH = 4, Temp = 303K, Contact Time = 70min.
S. No
Dye
conc.
(mg/L)
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.016 0.9 9.55 -
0.045 0.980 0.094 95.5
2 40 0.039 2.2 18.9 0.342 1.276 0.116 94.5
3 60 0.084 4.7 27.65 0.672 1.441 0.169 92.3
4 80 0.127 7.1 36.45 0.851 1.561 0.194 91.1
5 100 0.228 12.7 43.65 1.103 1.639 0.290 87.3
6 120 0.430 23.9 48.5 1.378 1.685 0.492 80.08
93
4.7.4 „Effect of pH
‟ on Adsorption of OG Dyes on RHC, KMRHC, RHA and KMRHA
The role of initial pH, on the dye adsorption was studied in range of 2-10., experimental
conditions of the removal of OG on RHC, KMRHC, RHA and KMRHA -adsorbents were: Initial
dye concentrations = 80mg/L, equilibrium agitation time, temperature = 303K and adsorbent
dose = 2g/L. It has been investigated that the dye adsorption on the adsorbents was increased
with the increase in initial pH. Maximum adsorption was inspected at pH = 4, then a slow and
gradual decrease was observed until pH = 8. A sharp decrease was investigated at initial pH>8 as
indicated in the figures 4.26, 4.27 and tables 4.17, 418, 4.19 and 4.20. The maximum dye
adsorption capacity of RHC, KMRHC, RHA and KMRHA was investigated as 26mg/g,
38.4mg/g, 23.05mg/g and 36.45mg/g respectively at pH = 4. The %adsorption of OG on RHC,
KMRHC, RHA and KMRHA was observed as 65.1%, 96% 57.6% and 91.1% respectively at the
same pH. At low pH value the surfaces of adsorbents were protonated which prefer to adsorb
anionic dye (OG). However at very low pH the concentration of proton is very high which may
interact with the anionic dye and hence decreasing the tendency of dye towards the adsorbents.
The maximum interaction of dye molecules with adsorbents was found at pH 4. At high pH, the
degree of protonation is decreased which results in a low dye adsorption value (Han, et at.,
2008). Moreover, at high pH value, the hydroxide ions concentration is high which compete the
OG dye (anionic dye), the former dominates, the positive surface potential of adsorbents
decrease which reduces the net ionic interaction between OG and adsorbent surfaces,
consequently the adsorption of dye decreases (Adegoke, et al., 2015). It was concluded that the
KOH modified adsorbents almost completely remove the Orange G (anionic dye) from aqueous
solution at pH = 4.
94
Figure‘4.26
„Effect of pH
‘ on Uptake Capacity (mg/g) of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media, Experimental Conditions
were: Adsorbent Dose = 2g/L, T = 303K, C0= 80 mg/L
0
5
10
15
20
25
30
35
40
24
68
10
qe
(m
g/g)
pH
RHC
KMRHC
RHA
KMRHA
95
Figure‘4.27 Effect of pH
‘ on % Adsorption of OG on RHC, KMRHC, RHA
and KMRHA, from Aqueous Media. Experimental Conditions were: Adsorbent
Dose = 2g/L, T = 303K, C0= 80 mg/L
0
20
40
60
80
100
120
0 2 4 6 8 10 12
% O
G A
dso
rpti
on
pH
RHC
KMRHA
RHA
KMRHA
96
Table 4.17 pH Optimization Study for Adsorption of Orange G dye on Rice Husk
Char. Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp = 303K,
Agitation Time = 60min.
Table 4.18 pH Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Char. Adsorbent Dose = 2g/L C0= 80mg/L, Temperature = 303K,
Contact Time = 80min
S. No pH
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2 0.295 16.4 31.8 79.5
2 4 0.057 3.2 38.4 96.0
3 6 0.136 7.6 36.2 90.5
4 8 0.210 11.7 34.1 85.3
5 10 0.655 36.4 21.8 54.5
S. No pH
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2 0.295 30.4 24.8 62.0
2 4 0.502 27.9 26.0 65.1
3 6 0.136 35.5 22.2 55.6
4 8 0.210 37.1 21.4 53.6
5 10 0.655 64.9 7.55 18.8
97
Table 4.19 pH Optimization Study for‗ Adsorption‘ of Orange G Dye on RHA,
Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp = 303K, Agitation
Time =60min.
S. No pH
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2 0.637 35.4 22.25 55.7
2 4 0.610 33.9 23.05 57.6
3 6 0.711 39.5 20.25 50.6
4 8 0.847 47.1 16.45 41.1
5 10 1.094 60.9 9.55 23.8
Table 4.20 pH Optimization Study for Adsorption of Orange G Dye on KOH
Modified Rice Husk Ash, Adsorbent Dose = 2g/L,C0= 80mg/L, Temperature =
303K,Contact Time = 70mins.
S. No pH
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2 0.205 11.4 34.3 85.75
2 4 0.127 7.1 36.45 91.1
3 6 0.280 15.6 32.2 80.5
4 8 0.426 23.7 28.15 70.3
5 10 0.599 33.4 23.3 58.2
98
4.7.5 „Effect of Temperature
‟ on Adsorption of OG Dye on RHC, KMRHC, RHA and
KMRHA
The removal of OG dye from aqueous media on RHC, KMRHC, RHA and KMRHA was
investigated at a temperatures range of 303-343K (303, 313, 323, 333 and 343 K±3). It was
inspected that the adsorption of OG from aqueous media decreases as the temperature increases.
Results of the adsorption study were illustrated in the figures4.28, 4.29 and tables 4.21, 4.22,
4.23 and 4.24 which indicated that both uptake capacity and % adsorption, were decreased as the
temperature increased from 303 to 343 K. The maximum adsorption capacity of OG dye on
RHC, KMRHC, RHA and KMRHA was investigated as 26mg/g, 38.4mg/g, 23.05mg/g and
36.45mg/g respectively at 303K. The %adsorption of OG on RHC, KMRHC, RHA and KMRHA
was observed as 65.1%, 96% 57.6% and 91.1% respectively at the same temperature. The fall in
the uptake capacity (mg/g) and %removal of dye with the increase in temperature indicated that
the adsorption of OG on RHC, KMRHC, RHA and KMRHA adsorbents is exothermic process.
99
Figure 4.28 „Effect of Temperature
‘ on Uptake Capacity (mg/g) of OG on
RHC, KMRHC, RHA And KMRHA from Aqueous Media. Experimental
Conditions were: Adsorbent Dose = 2g/L, C0= 80 mg/L
0
5
10
15
20
25
30
35
40
303313
323333
343
qe
(m
g/g)
Temperature (K)
OG
RHC
KMRHC
RHA
KMRHA
100
Figure 4.29 „Effect of Temperature‘ on% Removal of OG on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions were:
Adsorbent Dose = 2g/L, C0= 80 Mg/L
0
20
40
60
80
100
120
300 310 320 330 340 350
% O
G A
dso
rpti
on
Temperature (K)
RHC
KMRHC
RHA
KMRHA
101
Table 4.21 Temperature Optimization Study for Adsorption of Orange G Dye on Rice
Husk Char. Adsorbent Dose = 2g/L,C0= 80mg/L, pH = 4 Contact Time = 80min
S. No Temp (K) Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 303 0.502 27.9 26.0 65.1
2 313 0.531 29.5 25.2 63.1
3 323 0.136 35.3 22.3 55.8
4 333 0.210 39.7 20.1 50.3
5 343 0.655 47.8 16.1 40.2
Table 4.22 Temperature Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Char. Adsorbent Dose = 2g/L, C0= 80mg/L, pH = 4, Contact
Time = 80min.
S. No Temp (K)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 303 0.057 3.2 38.4 96.0
2 313 0.135 7.5 36.25 90.6
3 323 0.235 13.1 33.45 83.6
4 333 0.358 19.9 30.05 75.1
5 343 0.491 27.3 26.35 65.6
102
Table 4.23 Temperature Optimization Study for Adsorption of Orange G Dye on Rice
Husk Ash, Adsorbent Dose = 2g/L, C0= 80mg/L, pH = 4, Contact Time = 60min.
S. No Temp (K)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 303 0.610 33.9 23.05 57.6
2 313 0.635 35.3 22.3 55.8
3 323 0.660 36.7 21.65 54.1
4 333 0.685 38.1 20.95 52.3
5 343 0.714 39.7 20.1 50.3
Table 4.24 Temperature Optimization Study for Adsorption of Orange G Dye on
KOH Modified Rice Husk Ash. Adsorbent Dose = 2g/L, C0= 80mg/L, pH = 4, Contact
Time = 70min.
S. No Temp.(K)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 303 0.127 7.1 36.45 91.1
(2) 313 0.210 11.7 34.1 85.3
(3) 323 0.316 17.6 31.2 78.0
(4) 333 0.390 21.7 29.15 72.8
(5) 343 0.475 26.4 26.8 67.0
103
4.7.6 „Thermodynamic Studies‟
The thermodynamic‘ studies of adsorption of OG on RHC, KMRHC, RHA and KMRHA,
based on Gibbs free energy were investigated, using the following equation (Nethaji, et al.,
2010)
ΔG = − RT lnK (4.1)
Where R is gas constant [8.314 Jmol-1
K-1
]., T is temperature[Kelvin] and K is
‗equilibrium constant which was computed as:
K = Cads/Ce (4.2)
Cads is the adsorbed dye concentration on the surface of adsorbent and Ce is the
equilibrium dye concentration in solution. The value adsorption coefficient (K) decreases with
temperature, the highest value of adsorption coefficient was inspected at lower temperature as
indicated in the Table 4.25 which suggests that the rate of adsorption is high at low temperature.
This could also be supported by the exothermic nature of the process (−ΔH). The values of ΔG
are negative for the adsorption of OG on the adsorbents as illustrated in Table 4.25, which infers
for the spontaneous process. However the negative value of ΔG decreases at higher temperature
(Table 4.25), which suggests that the spontaneous nature of adsorption process decreases with
temperature. This might be due to high vibrational and kinetic energies of the dye molecules
which decrease the attractive forces of dye molecules towards the adsorbent. Moreover, at high
temperature the rate of desorption is relatively higher which decrease the adsorption efficiency
(Figures 4.28 and 4.29). In other words, it can be said that as compared to adsorbate–absorbent
interaction, the interaction of dye with the bulk/solvent becomes prominent with raising the
temperature. Hence at equilibrium the amount of adsorbed dye is lower at high temperature. The
free energy and temperature is related as (Moradi, et al., 2010)
ΔG = ΔH – TΔS (4.3)
The plots of ΔGVs T are shown in the figure‘4.30. Values of ΔS and ΔH could be
determined from the slopes and intercepts of the plots respectively. The thermodynamic,
104
parameters are given the table 4.25. The negative value of ΔH and ΔS inferred for exothermic
process for which the randomness decreases at the adsorbent/adsorbate interface.
Figure 4.30 Plots of ΔG Vs Temperature for the Adsorption of OG on RHC,
KMRHC, RHA and KMRHA from Aqueous Media at Co= 80 mg/L
y = 0.0675x - 22.313 R² = 0.9453
y = 0.151x - 53.428 R² = 0.9861
y = 0.0182x - 6.2899 R² = 0.9959
y = 0.0955x - 34.572 R² = 0.9773
-10
-8
-6
-4
-2
0
2
300 310 320 330 340 350
ΔG
(Kj/
mo
l)
Temperature (K)
RHC
KMRHC
RHA
KMRHA
105
Table 4.25 Thermodynamic Parameters, for Adsorption of OG dye on RHC, KMRHC, RHA
and KMRHA-adsorbents
Temp.
(K)
ΔG (kJ/mol) Values of (K)
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
303 -1.572 -8.005 -0.774 -5.867 1.867 24.0 1.359 10.26
313 -1.398 -5.899 -0.614 -4.591 1.711 9.66 1.266 5.837
323 -0.618 -4.374 -0.444 -3.398 1.259 5.10 1.179 3.545
333 -0.041 -3.059 -0.263 -2.736 1.015 3.02 1.102 2.686
343 1.126 -1.873 -0.042 -2.019 0.673 1.93 1.015 2.030
ΔH kJ/mol ΔS kj/mol/k
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
-22.31 -53.42 -6.289 -34.57 -0.067 -0.151 -0.018 -0.095
106
4.7.7 Adsorption Kinetics
Adsorption kinetics was studied for adsorption of OG on RHC, KMRHC, RHA and
KMRHA-adsorbents from aqueous solution. The pseudo.-first order kinetic model explains the
physical interaction of OG molecules with the adsorbent surface. This model claims that the rate.
of dye adsorption on the surface. of adsorbent is proportional to the available surface sites. Its
nonlinear form is given as (Sari & Tuzen 2009)
dqt/dt = k1 (qe−qt) (4.4)
Where qe. and qt. are the quantity of OG adsorbed at equilibrium and time t, K1. is rate
constant. This equation could be transformed to its linear form by integration.
log.(qe−qt) = log
.qe−K1t/2.303 (4.5)
K1 was obtained from the slop of the plot of log.(qe−qt) Vs t. The chemi-sorption nature
of OG on RHC, KMRHC, RHA and KMRHA-adsorbents was explained by Pseudo.-second
order equation. The nonlinear‘ form of this equation is given as follow (Abdelwaha, et al., 2013)
dqt/dt = k2 (qe−qt)2 (4.6)
This equation was integrated at the boundary conditions to convert into its linear form.
t/qt = t/qe + 1/k2 qe2 (4.7)
The values‘ of K2 and qe were calculated from the slope and intercept of the plot of t/qt
versus t respectively. Figures 4.31 and 4.32 indicated the plots of pseudo-.first and pseudo-
.second order reactions respectively
.. The values K1, K2, qe and R
2 for the adsorption of OG on
RHC, KMRHC, RHA and KMRHA are calculated from these plots and are illustrated in the
table 4.26. The adsorption of OG on RHC, KMRHC, RHA and KMRHA followed both the
kinetic models as inspected from the qe values, both of these are close to the experimental values
which reveals that the ‗adsorption was physico-chemical in nature. However, the value of
correlation factor (R2) for pseudo-second order is very high (R
2 > 0.99) which suggested that this
107
model is best fit to the kinetic data and the process of adsorption is mostly chemisorptions
(Zhang, et al., 2014)
Figure4.31 Pseudo-.First Order Kinetic‘ Models for Adsorption of OG on RHC,
KMRHC, RHA and KMRHA-Adsorbents
y = -0.0317x + 1.6145 R² = 0.9603
y = -0.0356x + 1.5985 R² = 0.9611
y = -0.03x + 1.1605 R² = 0.9626
y = -0.0191x + 1.2321 R² = 0.933
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 10 20 30 40 50 60
log(
qe−
qt)
t (min)
OG
RHC
KMRHC
RHA
KMRHA
108
Figure 4.32 Pseudo-.Second Order Kinetic Models for Adsorption of OG on RHC,
KMRHC, RHA and KMRHA-Adsorbents
Table 4.26 The Values of Rate. Constants
.K1 and K2, qe and Their R
2for the
Adsorption‘ of OG Dye on RHC, KMRHC, RHA and KMRHA-Adsorbents
Adsorbe
nt
Pseudo-.first order Pseudo-
.second order
K1.(min
-1) R
2. qe
.(mg/g) K2.(g/mg.min) R
2 qe(mg/g)
RHC 1.34×10-2
0.960 41.11 6.81×10-4
0.998 43.47
KMRHC 1.51×10-2
0.961 39.62 2.48×10-3
0.996 45.45
RHA 1.30×10-2
0.962 14.45 6.33×10-3
0.999 25.64
KMRHA 8.25×10-3
0.933 17.06 4.93×10-3
0.995 38.46
y = 0.0239x + 0.7765 R² = 0.9984
y = 0.0226x + 0.1956 R² = 0.9965
y = 0.0395x + 0.2406 R² = 0.9996
y = 0.0265x + 0.1377 R² = 0.9953
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60
t/ q
t
t (min)
OG RHC
KMRHC
RHA
KMRHA
109
4.7.8 Adsorption Isotherm Models
Adsorption equilibrium study is one of the most important studies, needed to
understand properly the adsorption procedure. An accurate perception and interpretation
of the adsorption isotherms is significant for the general step up of adsorption mechanism
and useful arrangement of adsorption scheme. In current times, ‗linear regression
analysis‘ is the most practical tool for defining the best fitting
‗adsorption model‘ because
it quantifies the allocation of adsorbates, evaluates the ‗adsorption system
‘, and proves
the reliability of theoretical suppositions of ‗adsorption isotherm model
‘. A brief
description of some very important isotherm models are given here to explain the
homogeneous, heterogeneous, mono-layer, multi-layer, physical and chemical nature of
adsorption process. It is also expected that application of these isotherm models to
current data may also result in extraction of something interesting from academic point
of view as well.
4.7.8.1 ‗Langmuir Adsorption Isotherm Model
‘
The Langmuir. model claims for the homogeneous adsorption. Its linear form is given as
Ce/qe = Ce/qm + 1 / Kqm (4.8)
Where Ce. is eq. conc. of OG (mg/L), qe
. is uptake capacity (mg/g), qm is the ‗maximum
monolayer coverage‘ (mg/g) and K is the Langmuir. constant (L mg
-1), which indicates the
adsorption energy. The values. of qm and K were computed from the intercepts and slopes of the
plots of Ce/qe Vs Ce (Suantak, et al.,2011).
4.7.8.2 ‗Freundlich Isotherm Model
‘
The Freundlich model‘ pretends for reversible and multilayer uptake. It assumes for the
heterogeneous adsorbent surface (Adamson, et al., 1997). Its linear form is as follow.
logqe = log.KF +1/n log
.Ce (4.9)
110
Where qe. is uptake capacity‘ (mg/g), Ce is equilibrium conc. of OG (mg/L)., KF and n are
‗Freundlich constants
‘ which claims for adsorption capacity (mg/g) and ‗adsorption intensity
, of
dye on the surface of KMRHC respectively. The values of KF and n were calculated from the
plot of logqe Vs logCe (Gurusamy, et al., 2002).
4.7.8.3 The Temkin Adsorption Isotherm Model
The Temkin model explains that the heat of adsorption decreases linearly with surface
coverage. Its linear form is given as (Boparai, et al., 2011).
qe = BlnKTK + BlnCe (4.10)
OR
qe = 2.303B logKTK + 2.303BlogCe (4.11)
Where B=RT/b., is Temkim isotherm constant, related to the heat of adsorption., KTK is
Temkin binding constant (L/mg) which claims for the maximum binding energy (Ahad, et al.,
2017). The values of B and KTK could be calculated from the slopes and intercepts of the plots of
qe Vs logCe. The values of b, R2and KTK are listed in Table 4.27. All the three models
(Langmuir., Freundlich
. and Temkin
.) for removal of OG from aqueous media on RHC,
KMRHC, RHA and KMRHA-adsorbents are depicted in the Figures 4.33, 4.34and 4.35. The
adsorption equilibrium data is fit to all the three models (R2> 0.90) as given in table 4.27 (Wang,
& Yan 2011; Kumar, et al., 2010). However, the data is best fit to the Langmuir isotherm model.
(R2
= 0.997). It suggests that the removal of OG on the surfaces of RHC, KMRHC, RHA and
KMRHA-adsorbents is mostly chemical sorption process. The values of R2 greater than 0.90 for
the adsorption of OG on RHC, KMRHC and KMRHA in the Freundlich model revealed for the
multilayer adsorption on the surfaces of these adsorbents. The high value of R2 for Temkin
model (R2> 0.96) for the adsorption of OG on KMRHC suggests that the surface of adsorbent is
heterogeneous (Behnamfard &Salarirad, 2009).
111
Figure 4.33 Langmuir Models for Adsorption of OG on RHC, KMRHC, RHA and
KMRHA-Adsorbents
y = 0.0308x + 0.2264 R² = 0.9988
0
0.5
1
1.5
2
2.5
0 20 40 60 80
Ce
/qe
Ce
RHC
y = 0.0173x + 0.0328 R² = 0.9979
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 5 10 15 20
Ce
/qe
Ce
KMRHC
y = 0.0302x + 0.4086 R² = 0.9812
0
0.5
1
1.5
2
2.5
0 20 40 60 80
Ce
/qe
Ce
RHA
y = 0.0172x + 0.0786 R² = 0.9983
0
0.1
0.2
0.3
0.4
0.5
0.6
0 10 20 30
Ce
/qe
Ce
KMRHA
112
Figure 4.34 Freundlich Isotherm Models for Adsorption of OG on RHC,
KMRHC, RHA and KMRHA-Adsorbents
y = 0.3749x + 0.8401 R² = 0.9567
y = 0.4569x + 1.2571 R² = 0.9102
y = 0.5452x + 0.6044 R² = 0.8247
y = 0.5025x + 1.0701 R² = 0.9516
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
-0.5 0 0.5 1 1.5 2
logq
e
log Ce
OG
RHC
KMRHC
RHA
KMRHA
113
Figure 4.35 Temkin Isotherm Models for‗ Adsorption of OG, on RHC, KMRHC, RHA
and KMRHA-Adsorbents
y = 15.025x + 3.1193 R² = 0.9836
y = 27.766x + 20.687 R² = 0.965
y = 14.901x + 0.1161 R² = 0.9601
y = 28.793x + 10.143 R² = 0.9882
0
10
20
30
40
50
60
-0.5 0 0.5 1 1.5 2
qe
logCe
OG RHC
KMRHC
RHA
KMRHA
114
Table 4.27 Parameters in Langmuir., Freundlich
. and Temkim Adsorption Isotherm
Models for Adsorption of OG Dye on RHC,KMRHC, RHA and KMRHA from Aqueous
Media.
Adsorption
Isotherm
Models
Parameters RHC KMRHC RHA KMRHA
Langmuir
qm(mg/g) 33.33 58.8 33.33 58.8
KL.(L mg-1
) 0.132 0.531 0.073 0.218
R2 0.998 0.997 0.981 0.998
Freundlich
n 2.673 2.192 1.838 1.992
KF(L mg-1
) 6.918 18.07 4.017 11.71
R2 0.956 0.910 0.824 0.951
Temkin
b (j/mol) 386.3 209.05 389.4 201.5
KKT (L/mg) 1.613 5.561 1.018 2.250
R2 0.983 0.965 0.960 0.988
115
4.8 Adsorption of Titan Yellow (TY) Dye on RHC, KMRHC, RHA and KMRHA
4.8.1 Effect of ‗Contact Time on Adsorption‘ of TY Dye on RHC, KMRHC, RHA and
KMRHA
The ‗effect of contact time‘ on the adsorption of TY dye was investigated in the range, of
10-90min with time interval of 10 minutes. The equilibrium was established after 70.min for
RHC, 60.min for KMRHC & RHA and 70.min for KMRHA. The adsorption experiment was
performed at the initial dye conc. of 80 mg/L containing 2g/L of adsorbent dose at pH = 3.5 with
agitation speed of 240 rpm and temperature of 303K. Experimental results of the adsorption are
illustrated in the figures 4.36, 4.37 and tables 4.28, 4.29, 4.30 and 4.31 which indicated that the
adsorption capacity (mg/g) of TY on KMRHC increased in the first 50-60 minutes and then
remained constant. Similar effect was also inspected in section 4.7.1. However, variations in the
adsorption capacities and percent adsorptions were due the different nature of adsorbate (dye)
molecules. The adsorption capacity (mg/g) of TY on RHC, KMRHC, RHA and KMRHA was
investigated as 24.7mg/g, 37.05mg/g, 23.85mg/g and 35.73mg/g respectively at equilibrium
stirring time. The %adsorption of TY on RHC, KMRHC, RHA and KMRHA was observed as
61.8%, 92.6% 59.6% and 89.8% respectively at equilibrium. The high uptake capacity and %
adsorption of TY dye on KMRHC and KMRHA as compare to the corresponding RHC and
RHA was investigated which suggested that KOH modification of RHC and RHA made these
adsorbents highly porous (SEM Fig. 4.4A and 4.7A) with more energetic sites for adsorption of
dye from aqueous media.
116
Figure 4.36 Effect of ‗Contact Time‘ on the Uptake‘ Capacity (mg/g) of TY on
RHC, KMRHC, RHA and KMRHA from Aqueous Media, Experimental
Conditions were; pH = 3.5, T = 303K, Adsorbent Concentration = 2g/L, C0= 80
mg/L
0
5
10
15
20
25
30
35
40
10 20 30 40 50 60
Up
take
cap
acit
y (m
g/g)
Time (min)
TY
RHC
KMRHC
RHA
KMRHA
117
Figure 4.37 Effect of ‗Contact Time‘ on %.Adsorption of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions
were: pH = 3.5, T = 303K, Adsorbent Concentration = 2g/L, C0= 80 mg/L
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80
% T
Y A
dso
rpti
on
Time (min)
RHC
KMRHC
RHA
KMRHA
118
Table 4.28 Time Optimization Study for Adsorption of TY Dye on RHC, Co= 80
mg/L, pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L
S. No. Stirring
time (min)
Absorbance
of filtrate
Conc. of
filtrate Ce
(mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
1 10 1.368 57.4 11.3 28.2
2 20 1.111 46.3 16.8 42.1
3 30 0.914 38.1 20.9 52.3
4 40 0.876 36.5 21.7 54.3
5 50 0.806 33.6 23.2 58.0
6 60 0.751 31.3 24.3 60.8
7 70 0.732 30.5 24.7 61.8
8 80 0.732 30.5 24.7 61.8
119
Table 4.29 Time Optimization Study for the Adsorption of TY Dye on KOH
Modified Rice Husk Char. Co= 80 mg/L, pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L,
S. No.
Stirring
time (min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye adsorbed
qe (mg/g)
% Dye
adsorbed
1 10 0.852 33.5 23.2 58.1
2 20 0.624 26.0 26.0 67.5
3 30 0.410 17.1 31.4 78.6
4 40 0.321 13.7 33.1 82.8
5 50 0.158 6.6 36.7 91.7
6 60 0.141 5.9 37.05 92.6
7 70 0.141 5.9 37.05 92.6
120
Table 4.30 Time Optimization Study for Adsorption of TY Dye on RHA. Co =
80 mg/L, pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L
S. No Stirring
time (min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed qe
(mg/g)
% Dye
adsorbed
1 10 1.353 56.4 11.8 29.5
2 20 1.183 49.3 15.35 38.3
3 30 1.015 42.3 18.85 47.1
4 40 0.916 38.2 20.9 52.2
5 50 0.808 33.7 23.15 57.7
6 60 0.775 32.3 23.85 59.6
7 70 0.775 32.3 23.85 59.6
121
Table 4.31 Time Optimization Study for Adsorption of TY Dye on KMRHA. Co = 80
mg/L, pH = 3.5, Temp = 303K, Adsorbent Dose = 2g/L
S. No
Stirring
time
(min)
Absorbance
of filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed qe
(mg/g)
% Dye
adsorbed
1 10 0.900 37.5 21.25 53.1
2 20 0.696 29.0 25.5 63.7
3 30 0.554 23.1 28.45 71.1
4 40 0.472 19.7 30.15 75.3
5 50 0.302 12.6 33.7 84.2
6 60 0.225 9.4 35.3 88.25
7 70 0.194 8.1 35.93 89.8
8 80 0.194 8.1 35.93 89.8
122
4.8.2 Effect.
of Adsorbent-.Dose on Adsorption of TY on RHC, KMRHC, RHA and
KMRHA
The effect of adsorbent.-dose on adsorption of TY on RHC, KMRHC, RHA and
KMRHA from aqueous media was investigated in the dose range of 1−5 g/L. The adsorption
experiment was performed for equilibrium time using 50 ml of 80 mg/L of ‗dye solution‘ at 303K
and pH = 3.5. Results of this study were listed in the figures 4.38, 4.39 and tables 4.32, 4.33,
4.34 and 4.35, which indicated that uptake capacity was decreased with the increase in adsorbent
dose. The highest adsorption capacity for TY was investigated as 31.9mg/g, 48mg/g, 30.3mg/g
and 43.7 mg/g on 1g/L of the RHC, KMRHC, RHA and KMRHA respectively. However, the
%.adsorption of TY increased for high adsorbent
.-dose due to the availability of more active sites
of the adsorbents. Comparable results were also inspected for ‗adsorption of OG dye as reported
in section 4.7.2.
123
Figure 4.38 Effect of Adsorbent.-Dose on the Uptake Capacity (mg/g) of TY
on RHC, KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: pH = 3.5, T = 303K, C0 = 80 mg/L
0
5
10
15
20
25
30
35
40
45
50
1 23
45
qe
(m
g/g)
Adsorbent dose (g/L)
TY
RHC
KMRHC
RHA
KMRHA
124
Figure 4.39 Effect of Adsorbent-.Dose on the %
.Adsorption of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions
were: pH = 3.5, T = 303K, C0 = 80 mg/L
0
20
40
60
80
100
120
0 1 2 3 4 5 6
% T
Y a
dso
rpti
on
Adsorbent dose (g/L)
RHC
KMRHC
RHA
KMRHA
125
Table 4.32 Adsorbent Dose Optimization Study for Adsorption of TY Dye on
RHC, Co = 80 mg/L, pH = 3.5, Temp = 303K, Agitation Time =70min,
Table 4.33 Weight Optimization Study for Adsorption of TY on KOH
Modified Rice Husk Char. Co = 80 mg/L, pH = 3.5, Temp = 303K, Contact Time =
60min
S. No. Adsorbent
dose (g/L).
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 1.154 48.1 31.9 39.8
(2) 2 0.732 30.5 24.7 61.8
(3) 3 0.628 26.2 17.9 67.2
(4) 4 0.520 21.7 14.5 72.8
(5) 5 0.448 18.7 12.2 76.6
S. No. Adsorbent
dose (g/L).
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.768 32 48.0 60.0
(2) 2 0.141 5.9 37.05 92.6
(3) 3 0.088 3.7 25.4 95.3
(4) 4 0.074 3.1 19.2 96.1
(5) 5 0.062 2.6 15.4 96.7
126
Table 4.34 Adsorbent Dose Optimization Study for Adsorption of TY Dye on Rice
Husk Ash. Co= 80 mg/L, pH = 3.5, Temp = 303K, Agitation Time =70min
Table 4.35 Weight Optimization Study for Adsorption of TYD ye on KOH Modified
Rice Husk Ash. Co = 80 mg/L, pH = 3.5, Temp = 303K, Contact Time = 60mins
S. No. Adsorbent
dose (g/L).
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 0.871 36.3 43.7 54.6
(2) 2 0.194 8.1 35.93 89.8
(3) 3 0.112 4.7 25.1 94.1
(4) 4 0.093 3.9 19.02 95.1
(5) 5 0.076 3.2 15.3 96.0
S. No. Adsorbent
dose (g/L).
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
(1) 1 1.192 49.7 30.3 37.8
(2) 2 0.775 32.3 23.85 59.6
(3) 3 0.679 28.3 17.23 64.6
(4) 4 0.583 24.3 13.92 69.6
(5) 5 0.447 19.9 12.02 75.1
127
4.8.3 ‗Effect of Dye Concentration
‘ on Adsorption of TY on RHC, KMRHC, RHA and
KMRHA
The removal of TY from aqueous media on RHC, KMRHC, RHA and KMRHA was
investigated at initial conc., ranging from 20-120 mg/L. The experiment was performed at 303K
and pH 3.5 for equilibrium stirring time using 2g/L of adsorbent dose. Results of the adsorption
experiments are shown in the figures4.40, 4.41 and tables 4.36, 4.37, 4.38and 4.39., which
indicated high adsorption capacity‘ (mg/g) of TY on the adsorbents for more concentrated
solution. The maximum adsorption capacity of TY on RHC, KMRHC, RHA and KMRHA was
investigated as 28.9 mg/g, 49.75 mg/g, 29.15 mg/g and 45.95mg/g respectively, at initial dye
conc. of 120 mg/L. The percentage adsorption of TY from aqueous media was declined with the
raise in initial dye conc. The maximum percentage removals of TY dye on RHC, KMRHC, RHA
and KMRHA was investigated as88%, 96%, 84.5% and 94.5% respectively at 20 mg/L of the
initial dyes concentrations. Similar results were also reported in section 4.7.3 for adsorption of
OG. Slight variances in the results of the two dyes adsorbed on the same adsorbent indicated that
adsorbent/adsorbate interaction could also be affected by changing the nature of adsorbate (dye).
128
Figure 4.40 Effect of ‗Initial Dye Concentration
‘ on Uptake Capacity of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions were; pH
= 3.5, T = 303K, Adsorbent Dose = 2g/L
0
5
10
15
20
25
30
35
40
45
50
20 40 6080
100120
qe
(m
g/g)
Conc. (mg/L)
TY
RHC
KMRHC
RHA
KMRHA
129
Figure 4.41 Effect of ‗Initial Dye Conc. on %.Adsorption of TY on RHC, KMRHC,
RHA and KMRHA from Aqueous Media. Experimental Conditions were: pH = 3.5, T =
303K, Adsorbent Dose = 2g/L
30
40
50
60
70
80
90
100
0 50 100 150
% T
Y A
dso
rpti
on
Conc. (mg/L)
RHC
KMRHC
RHA
KMRHA
130
Table 4.36 Concentration Optimization Study for ‗Adsorption‘ of TY Dye on RHC,
Adsorbent Dose = 2g/L, pH = 3.5, Temp = 303K, Agitation Time =70 min
S. No
Dye
conc.
(mg/L)
Absorbanc
e of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.081 3.4 8.3 0.531 0.919 0.409 83.0
2 40 0.271 11.3 14.3 1.053 1.155 0.790 71.7
3 60 0.475 19.8 20.1 1.296 1.303 0.985 67.0
4 80 0.732 30.5 24.7 1.484 1.392 1.234 61.8
5 100 1.101 45.9 27.05 1.661 1.432 1.696 54.1
6 120 1.636 62.2 28.9 1.793 1.460 2.152 48.1
131
Table 4.37 Concentration Optimization Study for the Adsorption of TY Dye on KOH
Modified Rice Husk Char, Adsorbent Dose = 2g/L, pH = 3.5, Temp = 303K, Contact Time =
60min
S. No
Dye
conc.
(mg/L)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.019 0.8 9.6 -0.096 0.982 0.083 96.0
2 40 0.064 2.7 18.6 0.431 1.269 0.145 93.2
3 60 0.093 4.3 27.8 0.633 1.444 0.154 92.8
4 80 0.141 5.9 37.05 0.770 1.568 0.159 92.6
5 100 0.309 12.9 43.5 1.110 1.638 0.296 87.1
6 120 0.492 20.5 49.75 1.311 1.696 0.412 82.9
132
Table 4.38 Concentration Optimization Study for ‗Adsorption‘ of TYD ye on RHA,
Adsorbent Dose = 2g/L, pH = 3.5, Temp = 303K, Agitation Time =70 min
S. No
Dye
conc.
(mg/L)
Absorbance
of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.074 3.1 8.45 0.491 0.926 0.366 84.5
2 40 0.292 12.2 13.9 1.086 1.143 0.877 69.5
3 60 0.501 20.9 19.55 1.320 1.291 1.069 65.1
4 80 0.775 32.3 23.85 1.509 1.377 1.354 59.6
5 100 1.149 47.9 26.05 1.680 1.415 1.838 52.1
6 120 1.480 61.7 29.15 1.790 1.464 2.166 48.5
133
Table 4.39 Concentration Optimization Study for Adsorption of TY Dye on KOH Modified
Rice Husk Ash. Adsorbent Dose = 2g/L pH = 3.5, Temp = 303K Contact Time = 60min
S. No
Dye
conc.
(mg/L)
Absorbanc
e of the
filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
logCe logqe Ce/qe % Dye
adsorbed
1 20 0.026 1.1 9.45 0.041 0.975 0.116 94.5
2 40 0.081 3.4 18.3 0.531 1.262 0.185 91.5
3 60 0.136 5.7 27.15 0.755 1.433 0.209 90.5
4 80 0.194 8.1 35.93 0.908 1.555 0.225 89.8
5 100 0.405 16.9 41.55 1.227 1.618 0.406 83.1
6 120 0.674 28.1 45.95 1.448 1.662 0.611 76.5
134
4.8.4 Effect of ‗pH on Adsorption‘ of TY Dye on RHC, KMRHC, RHA and KMRHA
The effect of initial pH on ‗adsorption‘ process was deliberated in the pH range of 2-6.,
other conditions of the removal of TY on RHC, KMRHC, RHA and KMRHA-adsorbents were:
Initial dye concentrations = 80mg/L, equilibrium agitation time, temperature = 303K and
adsorbent dose = 2g/L. It was investigated that ‗adsorption of dye on the adsorbents increases‘
with the increase in pH of solution. Maximum adsorption was inspected at pH = 3.5, then a slow
and gradual decrease was inspected up to pH 4.5 and afterward a sharp decrease was observed as
indicated in the figures 4.42, 4.43 and tables 4.40, 4.41, 4.42 and 4.43. The maximum dye
adsorption capacity of RHC, KMRHC, RHA and KMRHA was investigated as 24.7mg/g,
37.05mg/g, 23.85mg/g and 35.93mg/g respectively at pH = 3.5. The %adsorption of TY on
RHC, KMRHC, RHA and KMRHA was observed as 61.8%, 92.6%, 59.6% and 89.8%
respectively at the same pH; at low pH value the surfaces of adsorbents were protonated which
prefer to adsorb anionic dye. However at very low pH the concentration of protons (H+) is very
high that interact with the anionic dye, hence decreasing its affinity towards the adsorbent which
resulted into low adsorption of TY dye on the surface of adsorbents. The best interaction of TY
with adsorbents was inspected at pH 3.5, Further increase in the pH have lowered the adsorption
of dye because at high pH, the degree of protonation is decreased and hence the dye adsorption
was decreased (similar report is mentioned in section 4.7.4). It was concluded that the KOH
modified adsorbents have the potential to remove TY dye from solution almost completely at pH
3.5.
135
Figure. 4.42 ‗Effect of pH‘ on the Uptake Capacity (mg/g) of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions
were: Adsorbent dose = 2g/L, T = 303K, C0 = 80 mg/L
10
15
20
25
30
35
40
2 2.5 3 3.5 4 4.5 5 5.5 6
qe
(m
g/g)
pH
TY
RHC
KMRHC
RHA
KMRHA
136
Figure 4.43 ‗Effect of pH‘ on the %.Adsorption of TY on RHC, KMRHC, RHA
and KMRHA from Aqueous Media. Experimental Conditions were: Adsorbent
Dose = 2g/L, T = 303K, C0 = 80 mg/L
30
40
50
60
70
80
90
100
1.5 2.5 3.5 4.5 5.5 6.5
% T
Y A
dso
rpti
on
pH
RHC
KMRHC
RHA
KMRHA
137
Table 4.40 pH Optimization Study for the ‗Adsorption of TY‘ Dye on RHC,
Adsorbent Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp = 303K, Agitation
Time =70min
S. No pH Absorbance of
the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2.0 0.849 35.4 22.3 55.7
2 2.5 0.813 33.9 23.05 57.6
3 3.0 0.780 32.5 23.75 59.3
4 3.5 0.732 30.5 24.7 61.8
5 4.0 0.741 30.9 24.55 61.3
6 4.5 0.760 31.7 24.1 60.3
7 5.0 .0883 36.8 21.6 54.0
8 5.5 0.940 39.2 20.4 51.0
9 6.0 1.029 42.9 18.55 46.3
138
Table 4.41 ‗pH‘ Optimization Study for the Adsorption of TY Dye on KOH Modified
Rice Husk Char. Adsorbent Dose = 2g/L, C0= 80mg/L, Temperature = 303K,Contact
Time = 80mins
S. No pH Absorbance of
the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2.0 0.345 14.4 32.8 82.0
2 2.5 0.271 11.3 34.35 85.8
3 3.0 0.208 8.7 35.65 89.1
4 3.5 0.141 5.9 37.05 92.6
5 4.0 0.160 6.7 36.6 91.5
6 4.5 0.220 9.2 35.4 88.5
7 5.0 0.427 17.8 31.1 77.7
8 5.5 0.525 21.9 29.05 72.6
9 6.0 0.607 25.3 27.35 54.7
139
Table 4.42 pH Optimization Study for ‗Adsorption‘ of TY Dye on RHA, Adsorbent
Dose = 2g/L, Initial Dye Concentration = 80mg/L, Temp = 303K, Equilibrium Agitation
Time,
S. No pH Absorbance of
the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2.0 0.940 39.2 20.4 51.0
2 2.5 0.883 36.8 21.6 54.0
3 3.0 0.852 35.1 22.45 56.1
4 3.5 0.775 32.3 23.85 59.6
5 4.0 0.780 32.5 23.75 59.3
6 4.5 0.811 33.8 23.1 57.7
7 5.0 0.892 37.2 21.4 53.5
8 5.5 0.998 41.6 19.2 48.0
9 6.0 1.068 44.5 17.75 44.3
140
Table 4.43 pH Optimization Study for the Adsorption of TY Dye on KOH Modified
Rice Husk Ash, Adsorbent Dose = 2g/L, C0= 80mg/L, Temperature = 303K, Contact
Time = 80mins.
S. No pH Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 2.0 0.465 19.4 30.3 75.7
2 2.5 0.362 15.1 32.45 81.1
3 3.0 0.220 9.2 35.4 88.5
4 3.5 0.194 8.1 35.93 89.8
5 4.0 0.208 8.7 35.65 89.1
6 4.5 0.271 11.3 34.35 85.8
7 5.0 0.475 19.8 30.1 75.2
8 5.5 0.597 24.9 27.55 68.8
9 6.0 0.679 28.3 25.85 64.6
141
4.8.5 ‗Effect of Temperature‗
on Adsorption of TY Dye on RHC, KMRHC, RHA and
KMRHA
The removal of TY dye from aqueous media on RHC, KMRHC, RHA and KMRHA was
investigated at varied temperatures, (303, 313, 323, 333 and 343 K±3). Low adsorption results of
TY were inspected at high temperature as illustrated in the figures 4.44, 4.45 and tables 4.44,
4.45, 4.46 and 4.47 which indicated that the maximum dye adsorption capacities of RHC,
KMRHC, RHA and KMRHA were investigated as 24.7mg/g, 37.05mg/g, 23.85mg/g and
35.93mg/g respectively at 303K. The %adsorption of TY on RHC, KMRHC, RHA and KMRHA
was observed as 61.8%, 92.6%, 59.6% and 89.8% respectively at 303K. The decrease in uptake
capacity (mg/g) and %.removal at high temperature indicated that the adsorption of TY on RHC,
KMRHC, RHA and KMRHA adsorbents is exothermic process like that reported in section
4.7.5. At high temperature the interaction of dye with the bulk/solvent is high as compare to that
with the adsorbents which decrease the adsorption of dye on the adsorbents.
142
Figure 4.44 ‗Effect of Temperature‘ on the Uptake Capacity. (mg/g) of TY on
RHC, KMRHC, RHA and KMRHA from Aqueous Media. Experimental
Conditions were: Adsorbent Dose = 2g/L, C0= 80 mg/L
0
5
10
15
20
25
30
35
40
303313
323333
343
qe
(m
g/g)
Temperature (K)
TY
RHC
KMRHC
RHA
KMRHA
143
Figure 4.45 ‗Effect of Temperature, on the %
.Removal of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media. Experimental Conditions
were: Adsorbent Dose = 2g/L, C0= 80 mg/L
40
50
60
70
80
90
100
300 310 320 330 340 350
% T
Y a
dso
rpti
on
Temperature (K)
RHC
KMRHC
RHA
KMRHA
144
Table 4.44 Temperature Optimization Study for‗ Adsorption‘ of TY Dye on RHC,
Adsorbent Dose = 2g/L,C0 = 80mg/L, pH = 3.5, Contact Time = 70 min
Table 4.45 Temperature Optimization Study for the Adsorption of TY Dye on KOH
modified Rice Husk Char. Adsorbent Dose =2g/L, C0 = 80mg/L, pH = 3.5, Contact Time
= 60min
S. No Temp.
(K)
Absorbance of
the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed qe
(mg/g)
% Dye
adsorbed
1 303 0.732 30.5 24.7 61.8
2 313 0.806 33.6 23.2 58.0
3 323 0.847 35.3 22.3 55.8
4 333 0.876 36.5 21.7 54.3
5 343 0.952 39.7 20.1 50.3
S. No Temp.
(K)
Absorbance of
the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed qe
(mg/g)
% Dye
adsorbed
1 303 0.141 5.9 37.05 92.6
2 313 0.218 9.1 35.45 88.6
3 323 0.328 13.7 33.1 82.8
4 333 0.453 18.9 30.55 76.3
5 343 0.607 25.3 27.35 68.3
145
Table 4.46 Temperature Optimization Study for ‗Adsorption‘ of TY Dye on RHA,
Adsorbent Dose = 2g/L, C0 = 80mg/L, pH = 3.5, Contact Time = 70 min
Table 4.47 Temperature Optimization Study for ‗Adsorption‘ of TY Dye on KMRHA,
Adsorbent Dose =2g/L, C0 = 80mg/L, pH = 3.5, Contact Time = 60min
S. No
Temp.
(K)
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 303 0.775 32.3 23.85 59.6
2 313 0.811 33.8 23.1 57.7
3 323 0.876 36.5 21.7 54.3
4 333 0.931 38.8 20.6 51.5
5 343 0.950 39.6 20.2 50.5
S. No Temp.
(K)
Absorbance
of the filtrate
Conc. of
filtrate
Ce(mg/L)
Dye
adsorbed
qe (mg/g)
% Dye
adsorbed
1 303 0.194 8.1 35.93 89.8
2 313 0.271 11.3 34.35 85.8
3 323 0.381 15.9 32.05 80.1
4 333 0.472 19.7 30.15 75.3
5 343 0.559 23.3 28.35 70.8
146
4.8.6 ‗Thermodynamic Studies‘
The thermodynamic study for the adsorption of TY on RHC, KMRHC, RHA and
KMRHA from aqueous media was investigated on the basis of Gibbs free energy as given in
equation (3), the equilibrium constant K was calculated using equation (4) (section 4.7.6). The
negative ΔG values for the adsorption of TY on RHC, KMRHC, RHA and KMRHA (Tab. 4.48)
inferred for the spontaneous process. The relationship between free energy and temperature is
given in eq. (5) (section 4.7.6).The plots of ΔGVs T are shown in the figure 4.46. Values of ΔS
and ΔH were computed from ‗slopes and intercepts‘ of these plots respectively. The
thermodynamic parameters are given the table 4.48. The negative value of ΔH and ΔS inferred
for exothermic process for which the randomness decreases at the adsorbent/adsorbate interface.
147
Figure 4.46 Plots of ΔG Vs Temperature for the Adsorption of TY on RHC,
KMRHC, RHA and KMRHA from Aqueous Media at Co= 80 mg/L
y = 0.0271x - 9.3906 R² = 0.9695
y = 0.1045x - 38.02 R² = 0.9998
y = 0.025x - 8.5631 R² = 0.9759
y = 0.0816x - 30.214 R² = 0.995 -7
-6
-5
-4
-3
-2
-1
0
1
300 310 320 330 340 350
ΔG
(kJ
/mo
l)
Temperature (K)
TY
RHC
KMRHC
RHA
KMRHA
148
Table 4.48 ‗Thermodynamic Parameters‘ for the Adsorption of TY Dye on RHC, KMRHC,
RHA and KMRHA-Adsorbents
Temp.
(K)
ΔG (kJ/mol) Values of (K)
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
303 -1.219 -6.374 -0.982 -5.500 1.622 12.559 1.476 8.876
313 -0.839 -5.342 -0.813 -4.696 1.380 7.791 1.366 6.079
323 -0.634 -4.234 -0.471 -3.743 1.266 4.839 1.191 4.031
333 -0.485 -3.248 -0.166 -3.097 1.191 3.232 1.061 3.060
343 -0.042 -2.198 -0.057 -2.536 1.015 2.162 1.020 2.433
ΔH kJ/mol ΔS kj/mol/k
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
-9.39 -38.02 -8.563 -30.21 -0.027 -0.104 -0.025 -0.081
149
4.8.7 Adsorption Kinetics
Adsorption kinetics for adsorption of TY on RHC, KMRHC, RHA and KMRHA-
adsorbents was studied. The pseudo.-first order kinetic ‗model explains physical interaction of
TY molecules with the adsorbent surface. It‘s nonlinear‘ and linear, forms are given in eq. (4.4
and 4.5) (section 4.7.7).The chemi-sorption nature of TY on RHC, KMRHC, RHA and
KMRHA-adsorbents is explained by Pseudo-second order equation. The nonlinear‘ and linear‘
forms of this model are given in eq. (4.6) and (4.7) (section 4.7.7). Figures 4.47 and 4.48
indicated the plots of pseudo.-first and pseudo
.-second order
, reactions respectively. The
numerical values of K.1, K2., qe and R2 for the adsorption of TY on RHC, KMRHC, RHA and
KMRHA were computed with the help of these plots which are demonstrated in the table 4.49.
The adsorption of TY on RHC, KMRHC, RHA and KMRHA followed both the kinetic models
as inspected from the qe values, both of these are close to the experimental values which
revealed that TY adsorbed on the adsorbents physico-chemically. However, the numerical value
of correlation factor (R2) for pseudo-second order was very high (R
2 > 0.98) for the adsorption of
TY dye on KMRHC, RHA and KMRHA which suggested that this model was best fit to the
kinetic data and the process of adsorption is dominantly chemisorption. Moreover, the
investigational statistical values of qe were found in concord with the computed ones for the
three adsorbents. Adsorption of TY dye on RHC followed the pseudo- first order reaction due to
its high value of correlation factor (R2>0.98). Moreover, the experimental qe value was matching
with the theoretical value as indicated in table 4.49.
150
Figure 4.47 Pseudo.-First Order
, Kinetic Models for Adsorption of TY on
RHC, KMRHC, RHA and KMRHA-Adsorbents
y = -0.0232x + 1.3478 R² = 0.9836
y = -0.0364x + 1.7071 R² = 0.8155
y = -0.0231x + 1.3596 R² = 0.9852
y = -0.0189x + 1.4011 R² = 0.9257
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 10 20 30 40 50 60
log(
qe−
qt)
t (min)
TY RHC
KMRHC
RHA
KMRHA
151
Figure 4.48 Pseudo.-Second Order Kinetic Models for the Adsorption of OG
on RHC, KMRHC, RHA and KMRHA-adsorbents
y = 0.0116x + 0.4114 R² = 0.8908
y = 0.023x + 0.2531 R² = 0.9832
y = 0.0324x + 0.5919 R² = 0.988
y = 0.0257x + 0.253 R² = 0.9883
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60
t/ q
t
t (min)
TY
RHC
KMRHC
RHA
KMRHA
152
Table 4.49 The Numerical Values of Rate Constants K1 andK2, qe and their R2for the
Adsorption of TY Dye on RHC, KMRHC, RHA and KMRHA-Adsorbents
Adsorbent
Pseudo.-first order Pseudo
.-second order
K1.(min-1
) R2
qe.
(mg/g) K2.(g/mg.min) R
2
qe.
(mg/g)
RHC 5.29×10-2
0.983 22.23 1.2×10-4
0.890 90.9
KMRHC 8.29×10-2
0.815 50.93 5.29×10-4
0.983 43.47
RHA 5.29×10-2
0.985 22.85 1.02×10-3
0.988 31.25
KMRHA 4.14×10-3
0.925 25.17 6.02×10-4
0.988 40.0
4.8.8 Adsorption Isotherm Models
The linear, form of Langmuir
,, Freundlich and Temkin models are given in eq. (4.8),
(4.9) and (4.10) or (4.11)respectively (section 4.7.8).All the three models (Langmuir,, Freundlich
and Temkin.) for, the amputation of TY from aqueous media on RHC, KMRHC, RHA and
KMRHA-adsorbents were depicted in the figures 4.49, 4.50 and 4.51. Numerical values of the
parameters in these models were listed in table 4.50. The adsorption equilibrium data is fit to all
of these models (R2> 0.90) as given in table 4.50. However, the data is best fit to Langmuir
,
isotherm [R2
greater than 0.98]. It suggested that TY was mostly chemically adsorbed on the
surfaces of RHC, KMRHC, RHA and KMRHA-adsorbents. The correlation
coefficientR2wasalso found to be greater than 0.90 for the adsorption of TY on RHC, KMRHC,
RHA and KMRHA in the Freundlich model which indicated that the surfaces of the adsorbents
are heterogeneous and the adsorption continued to multilayer formation.
153
Figure 4.49 Langmuir Models for Adsorption of TY on RHC, KMRHC, RHA
and KMRHA-Adsorbents
y = 0.0285x + 0.3899 R² = 0.9931
y = 0.0293x + 0.4081 R² = 0.9834
0
0.5
1
1.5
2
2.5
0 20 40 60 80
Ce
/qe
Ce
TY
RHC
RHA
y = 0.0162x + 0.0807 R² = 0.988
y = 0.018x + 0.1023 R² = 0.9937
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30
Ce
/qe
Ce
TY
KMRHC
KMRHA
154
Figure 4.50 Freundlich Isotherm for Adsorption of TY on RHC, KMRHC,
RHA and KMRHA-Adsorbents
y = 0.4461x + 0.6956 R² = 0.9832
y = 0.5225x + 1.0706 R² = 0.9534
y = 0.4242x + 0.7125 R² = 0.99
y = 0.5037x + 1.0053 R² = 0.9446
0.7
0.9
1.1
1.3
1.5
1.7
1.9
-0.5 0 0.5 1 1.5 2
logq
e
logCe
TY RHC
KMRHC
RHA
KMRHA
155
Figure 4.51 Temkin Isotherms for Adsorption of TY on RHC, KMRHC, RHA
and KMRHA-Adsorbents
y = 17.17x - 1.8138 R² = 0.9806
y = 29.917x + 10.312 R² = 0.9642
y = 16.15x - 1.0412 R² = 0.962
y = 27.577x + 7.1546 R² = 0.9699
0
10
20
30
40
50
60
-0.5 0 0.5 1 1.5 2
qe
logCe
TY
RHC
KMRHC
RHA
KMRHA
156
Table 4.50 Parameters in Langmuir,, Freundlich and Temkim Adsorption Isotherms for
Adsorption of TY on RHC, KMRHC, RHA and KMRHA-adsorbents
Adsorption
Isotherm
Models
Parameters RHC KMRHC RHA KMRHA
Langmuir
qm(mg/g) 35.75 62.5 34.48 55.5
KL.(L mg-1
) 0.0719 0.20 0.0710 0.176
R2 0.993 0.998 0.983 0.993
Freundlich
n 2.240 1.915 2.358 1.988
KF(L mg-1
) 4.954 11.74 5.152 10.11
R2 0.983 0.953 0.990 0.944
Temkin
b (j/mol) 337.9 194.07 359.04 210.45
KTK (L/mg) 0.784 2.212 0.862 1.817
R2 0.980 0.964 0.962 0.969
157
4.9 Adsorption of Pb2+
on RHC, KMRHC, RHA and KMRHA
4.9.1 Time Optimization Study for Adsorption of Pb2+
on RHC, KMRHC, RHA and
KMRHA-Adsorbents
To investigate the optimum time for the adsorption of Pb2+
on RHC, KMRHC, RHA and
KMRHA, the experiment was performed at the agitation time ranging from 10 – 90 min with
time interval of 10 min at experimental conditions; initialPb2+
ions conc. of 250 mg/L containing
2g/L of the adsorbent dose at pH = 6 with stirring speed of 240 rpm at 303K. Experimental
results were illustrated in the figures 4.52, 4.53 and tables 4.51, 4.52, 4.53 and 4.54 which
indicated that maximum adsorption capacities (mg/g) of Pb2+
on RHC, KMRHC, RHA and
KMRHA-adsorbents were 92.2, 119.9, 86.75 and 113.7 mg/g. This suggested that the
modification of RHC with KOH enhanced its adsorption capacity from 92.2 to 119.9mg/g while
that of RHA from 86.75 and 113.7 mg/L. Equilibrium (optimum) agitation time for Pb2+
removal, was investigated as 50 min each on RHC and KMRHC as indicated in the tables 4.51
and 4.52, However the equilibrium is reached after 80 and 70 min for the adsorption of Pb2+
ions
on RHA and KMRHA respectively as shown in the tables 4.53 and 4.54. It indicated that
adsorption rate on the surfaces of RHC and KMRHC is comparatively higher than that on RHA
and KMRHA. It also suggested that after 50 minutes the available binding sites of RHC and
KMRHC are saturated and the Pb2+
ions concentration reaches to its minimum whereas the
surfaces of RHA and KMRHA are saturated after 80 and 70 min respectively. From the figures
and tables the maximum adsorption efficiencies of Pb2+
ions were noted as 74%, 95.9%, 86.75%
and 90.6% on RHC, KMRHC, RHA and KMRHA respectively, which revealed that percent
adsorption of Pb2+
ions on KMRHC and KMRHA are greater than the corresponding values of
RHC and RHA. These results inferred for the high efficiencies of the KOH modified adsorbents.
158
Figure 4.52 Time Optimization Study for the Adsorption Capacity (mg/g) of
Lead Ions on RHC, KMRHC, RHA and KMRHA, Co = 250 mg/L, pH = 6, Temp =
303K,Adsorbent Dose = 2g/L
40
50
60
70
80
90
100
110
120
130
10 20 30 40 50 60
qm
(m
g/g)
Time (min)
Pb2+
RHC
KMRHC
RHA
KMRHA
159
Figure 4.53 Time Optimization Study for the %.Adsorption of Lead Ions on
RHC, KMRHC, RHA, and KMRHA. Co = 250 mg/L, pH = 6, Temp = 303K,
Adsorbent Dose = 2g/L
0
20
40
60
80
100
120
0 20 40 60 80
%P
b2
+ ad
sorb
ed
Time (min)
RHC
KMRHC
RHA
KMRHA
160
Table 4.51 Time Optimization Study for Adsorption of Lead Ions on Rice Husk Char.
Co = 250 mg/L, pH = 6, Temp = 303K, Adsorbent Dose = 2g/L
Table 4.52 Time Optimization Study for Adsorption of Lead Ions on KMRHC Co =
250 mg/L, pH = 6, Temp = 303K, Adsorbent Dose = 2g/L
S. No Stirring
time (min)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qt (mg/g)
%Pb2+
adsorbed
1 10 115.0 67.5 54.0
2 20 94.1 77.95 62.3
3 30 78.6 85.7 68.5
4 40 68.3 90.85 72.6
5 50 65.0 92.2 (qe) 74.0
6 60 65.0 92.2 (qe) 74.0
S. No Stirring time
(min)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qt (mg/g)
%
Pb2+
adsorbed
1 10 55.0 97.5 78
2 20 34.1 107.9 86.3
3 30 22.6 113.7 90.9
4 40 14.3 117.85 94.28
5 50 10.2 119.9 (qe) 95.9
6 60 10.2 119.9 (qe) 95.9
161
Table 4.53 Time Optimization Study for Adsorption of Pb2+
on RHA, Co = 250 mg/L,
pH = 6, Temp = 303K, Adsorbent Dose = 2g/L
S. No Stirring time
(min)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed qt
(mg/g)
% pb2+
adsorbed
1 10 135.0 57.5 46
2 20 109 70.5 56.4
3 30 98.6 75.7 60.5
4 40 88.3 80.85 64.6
5 50 82.0 84.0 67.2
6 60 79.0 85.5 68.4
7 70 77.0 86.5 69.2
8 80 76.5 86.75 (qe) 69.4
9 90 76.5 86.75(qe) 69.4
162
Table 4.54 Time Optimization Study for Adsorption ofPb2+
on RHA, Co = 250 mg/L,
pH = 6, Temp = 303K, Adsorbent Dose = 2g/L
S. No Stirring
time (min)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qt (mg/g)
% Pb2+
adsorbed
1 10 102 74 59.2
2 20 79.0 85.5 68.4
3 30 65.0 92.2 74.0
4 40 50.7 99.65 79.7
5 50 34.1 107.9 86.3
6 60 27.6 111.2 88.9
7 70 22.6 113.7 (qe) 90.9
8 80 22.6 113.7 (qe) 90.9
163
4.9.2 ‗Effect of Adsorbent Dose on Adsorption of Pb2+
on RHC, KMRHC, RHA and
KMRHA-Adsorbents
Variable adsorbent dose ranging from 1 to 5 g/L was employed to study it‘s effect on the
removal of Pb2+
ions on RHC, KMRHC, RHA and KMRHA-adsorbents from aqueous solution.
50. ml of 250
. mg/L of Pb
2+.solutions were employed at 303 K and pH = 6 for the adsorption
experiments. Results of this study are listed in figures 4.54, 4.55 and tables 4.55, 4.56, 4.57 and
4.58 which indicated low adsorption capacities (mg/g) for high adsorbent dose at the same
concentration of Pb2+
in solution. The upper limit of adsorption capacity for Pb2+
on RHC,
KMRHC, RHA and KMRHA was inspected as 136mg/g, 172mg/g, 106mg/g and 152 mg/g
respectively on 1g/L of each of the adsorbent. It suggested that the adsorption of metal cat-ions
(Pb2+
) on the KOH modified RHC and RHA was extremely high as compared to that on RHC
and RHA. The increase in the adsorption capacity from 114 mg/g to172 mg/g and 106 mg/g to
152 mg/g suggested that KOH modification of RHC and RHA enhanced their adsorption
capacity to maximum values. The highest adsorption capacities for the lowest value of adsorbent
dose inferred that for limited surface sites the available Pb2+
ions are high, which afford to
enhance the adsorption capacity of adsorbents. This might be due to the multilayer formation on
the surface of adsorbents, which is also confirmed by the high value of correlation factor in the
Fruendlich isotherm model (Table 4.73). However, the % adsorptions of the Pb2+
ions are
lowered at low adsorbent does. The %adsorption of the Pb2+
is increased for high adsorbent dose
as indicated in the figure 4.55. It revealed that the availability of surface active sites of the
adsorbent are increased which attributes for the high values of %.adsorption of Pb
2+ on
adsorbents (Kulkarni, et al., 2012).The figure 4.55 indicated that %.adsorption of Pb
2+was
increased for high adsorbent dose and reached to its maximum level at 5g/L for each adsorbent.
Further increase in the adsorbent concentration doesn‘t affect the percent removal of the
Pb2+
from aqueous media which inferred that maximum of Pb2+
ions have been removed and its
conc. in the solution reached to minimum level (Nomanbhay & Palanisamy, 2005).
164
Figure 4.54 Effect of Adsorbent.-Dose on Adsorption Capacity of Pb
2+on RHC,
KMRHC, RHA and KMRHA-Adsorbents
0
20
40
60
80
100
120
140
160
180
0 1 2 3 4 5
qm
(m
g/g)
adsorbent dose (g/L)
Pb 2+
RHC
KMRHC
RHA
KMRHA
165
Figure 4.55 Effect of Adsorbent-.Dose on % Adsorption of Pb
2+ on RHC,
KMRHC, RHA and KMRHA-Adsorbents
0
20
40
60
80
100
120
0 1 2 3 4 5 6
% P
b A
dso
be
d
Adsorbent dose (g/L)
RHC
KMRHC
RHA
KMRHA
166
Table 4.55 Weight Optimization Study for, Adsorption of Pb
2+ on RHC, Co = 250
mg/L, pH = 6, Temp = 303K Agitation Time = 50min
S. No Adsorbent dose
(g/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
% Pb2+
adsorbed
(1) 1 136 114 45.6
(2) 2 65.0 92.2 74.0
(3) 3 51.1 66.3 79.5
(4) 4 45.7 51.07 81.72
(5) 5 38.1 42.3 84.7
Table 4.56 Weight Optimization Study for, Adsorption of Pb
2+ on KMRHC, Co = 250
mg/L, pH = 6, Temp = 303K Agitation Time = 50min
S. No Adsorbent
dose(g/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
% Pb2+
adsorbed
(1) 1 78.0 172.0 68.8
(2) 2 10.2 119.9 95.9
(3) 3 7.6 80.8 96.9
(4) 4 6.4 60.9 97.4
(5) 5 5.9 48.8 97.6
167
Table 4.57 Weight Optimization Study for,
Adsorption of Pb2+
on RHA, Co = 250
mg/L, pH = 6, Temp = 303K, Agitation Time = 80min
S. No Adsorbent dose
(g/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
% Pb2+
adsorbed
(1) 1 144 106 42.4
(2) 2 76.5 86.75 69.4
(3) 3 61.1 62.96 75.5
(4) 4 55.2 48.7 77.9
(5) 5 48.8 40.2 80.4
Table 4.58 Weight Optimization Study for, Adsorption of Pb
2+ on KMRHA, Co = 250
mg/L, pH = 6, Temp = 303K, Agitation Time = 70min
S. No Adsorbent
dose(g/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
% Pb2+
adsorbed
(1) 1 98.0 152 60.8
(2) 2 22.6 113.7 90.9
(3) 3 16.2 77.93 93.5
(4) 4 11.7 59.5 95.3
(5) 5 7.6 48.4 96.9
168
4.9.3 ‗Effect of Pb
2+.Conc.on‗Adsorption of Pb
2+‘on RHC, KMRHC, RHA and KMRHA
The effect of Pb2+
conc. on adsorption of Pb2+
on RHC, KMRHC, RHA and KMRHA was
studied in the range of 50-300 mg/L (50, 100, 150, 200, 250, 300mg/L). The adsorption
experiments were performed at 303K and pH = 6 for equilibrium agitation time using 2g/L of the
adsorbent dose. Results of the adsorption process are given in the figures 4.56, 4.57 and tables
4.59, 4.60, 4.61, & 4.62. Highest adsorption capacity was inspected for the concentrated solution
of Pb2+
. Maximum adsorption capacity for Pb2+
ions were investigated as 107mg/g, 138.7mg/g,
97mg/g and 131 mg/g on RHC, KMRHC, RHA and KMRHA respectively at Co = 300 mg/L. In
contrast the %.removal of Pb
2+was enhanced at lower conc. of Pb
2+solution as shown in the
figure 4.57. For low conc. of Pb2+
, the surface active sites of adsorbents are greater which could
remove the Pb2+
completely from aqueous media. However, for more concentrated solution of
Pb2+
, the surface active sites of the adsorbent became fewer to completely remove the Pb2+
from
aqueous solution. The maximum percentage removals of Pb2+
ions on the surfaces of RHC,
KMRHC, RHA and KMRHA-adsorbents were investigated as 83.6%, 98.7%, 90.6% and 96.4%
respectively. Hence these results indicated that KMRHC and KMRHA are efficient adsorbents
for the removal of Pb2+
from aqueous media.
169
Figure 4.56 Concentration Optimization Study for Adsorption Capacity of lead Ions on
RHC, KMRHC, RHA and KMRHA, Adsorbent Dose = 2g/L pH = 6, Temp = 303K,
0
20
40
60
80
100
120
140
160
50 100 150 200 250 300
qm
(m
g/g)
Concentration (mg/L)
Pb2+
RHC
KMRHC
RHA
KMRHA
170
Figure 4.57 Concentration Optimization Study for %.Adsorption of lead Ions on RHC,
KMRHC, RHA and KMRHA, Adsorbent Dose = 2g/L pH = 6, Temp = 303K,
60
65
70
75
80
85
90
95
100
105
0 100 200 300 400
%P
b2
+ A
dso
rbe
d
Concentration (mg/L)
RHC
KMRHC
RHA
KMRHA
171
Table 4.59 Concentration Optimization Study for Adsorption of Lead Ions on Rice Husk
Char. Adsorbent Dose = 2g/L, pH = 6, Temp = 303K, Agitation Time = 50min
S. No
Pb2+
conc.
(mg/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
logCe Logqe Ce/qe % Pb
2+
Adsorbed
1 50 1.5 24.25 0.176 1.384 0.061 97.0
2 100 16.4 41.8 1.214 1.621 0.392 83.6
3 150 32.4 58.8 1.510 1.769 0.551 78.4
4 200 49.1 75.4 1.691 1.877 0.651 75.4
5 250 65.0 92.2 1.812 1.964 0.704 74.0
6 300 86.0 107 1.934 2.029 0.803 71.3
172
Table 4.60 Concentration Optimization Study for Adsorption of Lead Ions on KOH Modified
Rice Husk Char. Adsorbent Dose = 2g/L, pH = 6, Temp = 303K, Agitation Time = 50min,
S. No
Pb2+
conc.
(mg/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
logCe Logqe Ce/qe % Pb
2+
Adsorbed
1 50 0.40 24.8 -0.937 1.394 0.016 99.2
2 100 1.30 49.35 0.113 1.693 0.026 98.7
3 150 4.71 72.64 0.673 1.861 0.0648 96.8
4 200 7.74 96.13 0.888 1.982 0.080 96.1
5 250 10.2 119.9 1.008 2.078 0.085 95.9
6 300 22.6 138.7 1.354 2.142 0.162 92.4
173
Table 4.61 Concentration Optimization Study for Adsorption of Pb2+
on RHA, Adsorbent
Dose = 2g/L, pH = 6, Temp = 303K,Agitation Time = 80min
S. No
Pb2+
conc.
(mg/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
logCe Logqe Ce/qe
%
Pb2+
Adso
rbed
1 50 4.7 22.65 0.672 1.355 0.207 90.6
2 100 23.4 38.5 1.369 1.585 0.607 76.6
3 150 44.4 52.8 1.647 1.722 0.840 70.4
4 200 59.6 70.2 1.775 1.846 0.849 70.2
5 250 76.5 86.75 1.883 1.938 0.881 69.4
6 300 106.0 97.0 2.025 2.025 1.092 64.6
174
Table 4.62 Concentration Optimization Study for Adsorption of Lead Ions on KOH Modified
Rice Husk Ash, Adsorbent Dose = 2g/L, pH = 6, Temp = 303K, Agitation Time = 70min.
S. No
Pb2+
conc.
(mg/L)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
logCe Logqe Ce/qe % Pb
2+
Adsorbed
1 50 1.8 24.1 0.255 1.382 0.074 96.4
2 100 5.1 45.9 0.707 1.661 0.111 94.9
3 150 9.6 70.2 0.982 1.846 0.137 93.6
4 200 16.7 91.65 1.222 1.962 0.181 91.65
5 250 22.6 113.7 1.354 2.055 0.198 90.9
6 300 37.4 131 1.572 2.117 0.285 87.5
175
4.9.4 Effect of pH on the Adsorption of Pb2+
on RHC, KMRHC, RHA and KMRHA-
Adsorbents
The pH could affect the surface polarity of adsorbent. Therefore it could control the
amputation of Pb2+
.from aqueous media. The effect of pH on removal of Pb2+
ions on the
surfaces of RHC, KMRHC, RHA and KMRHA was studied in the range of 3-6 at 250 mg./L of
initial Pb2+
conc. and 303 K using 2g/L of adsorbent dose. Results of the adsorption studies at
variable pH are listed in the Figures 4.58, 4.59 and tables 4.63, 4.64, 4.65 and 4.66. The
maximum adsorption capacity of metal ions on RHC, KMRHC, RHA and KMRHA were
investigated as 92.2mg/g, 119.9mg/g, 86.7mg/g and 113.7 mg/g respectively, as indicated in
figure 4.58. Figure 4.59 indicated that the highest percentage adsorptions of metal ions on the
RHC, KMRHC, RHA and KMRHA were also inspected at pH 6 as74%, 95.9%, 69.4% and
90.9% respectively. It is because in acidic media, the surfaces of adsorbents are highly
protonated which decrease the adsorption of Pb2+
. At high pH, ‗the degree of protonation
, on the
surface, of adsorbent, decreases gradually and thus the %
.removal ofPb
2+increases (Han, et al.,
2008). Moreover, at high pH the concentration of hydroxide ion is increased which increase the
negative surface potential of adsorbents and hence the adsorption of metal cat-ions increases
(Kadirvelu & Namasivayam, 2003). However the adsorption experiment was conducted at
controlled pH = 6 because the Pb2+
ions are precipitated as Pb(OH)2. at pH > 6.7 (Momĉilović.,et
al., 2011).
176
Figure 4.58 Effect of pH‘ on the Uptake Capacity of Pb
2+on RHC,
KMRHC, RHA and KMRHA
Figure 4.59 Effect of pH‘ on Percent Adsorption of Pb
2+ on RHC,
KMRHC, RHA and KMRHA
30
40
50
60
70
80
90
100
110
120
3 45
6
Up
take
cap
acit
y (m
g/g)
pH
Pb2+
RHC
KMRHC
RHA
KMRHA
30
40
50
60
70
80
90
100
2.5 3.5 4.5 5.5 6.5
% P
b2
+ ad
sorp
tio
n
pH
RHC
KMRHC
RHA
KMRHA
177
Table 4.63 pH Optimization Study for Adsorption ofPb2+
on RHC, Adsorbent
Dose = 2g/L Co = 250 mg/L, Temp = 303K, Agitation Time = 50min
Table 4.64 pH Optimization Study for Adsorption of Lead Ions on KOH
Modified Rice Husk Char, Adsorbent Dose = 2g/L, Co = 250 mg/L, Temp = 303K,
Agitation Time = 50min
S. No pH
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 3 143.7 53.15 42.2
2 4 97.8 76.1 60.8
3 5 78.5 85.7 68.6
4 6 65.0 92.2 74.0
S. No pH
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 3 143.7 53.5 42.8
2 4 77.8 86.1 68.8
3 5 25.5 112.25 89.8
4 6 10.2 119.9 95.9
178
Table 4.65 pH Optimization Study for Adsorption of Pb2+
onRHA, Adsorbent
Dose = 2g/L, Co = 250 mg/L, Temp = 303K,Agitation Time = 80min.
Table 4.66 pH Optimization Study for Adsorption of Lead Ions on KOH
Modified Rice Husk Ash, Adsorbent Dose = 2g/L, Co = 250 mg/L, Temp = 303K,
Agitation Time = 70min,
S. No pH
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 3 125.7 62.15 49.7
2 4 113.7 68.15 54.5
3 5 88.3 80.85 64.6
4 6 76.5 86.75 69.4
S. No pH
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 3 83.7 83.2 66.7
2 4 50.7 99.65 79.7
3 5 34.1 107.9 86.3
4 6 22.6 113.7 90.9
179
4.9.5 Effect of ‗Temperature on Adsorption of Pb
2+‘ on RHC, KMRHC, RHA and
KMRHA-Adsorbents
The removal of Pb2+
on RHC, KMRHC, RHA and KMRHA from aqueous solution was
studied at various temperatures (303, 313, 323, 333 and 343 K±3). Results of ‗adsorption studies‘
are given in figures 4.60, 4.61 and tables 4.67, 4.68, 4.69 and 4.70 which indicated that the
removal of Pb2+
on adsorbents‘ from aqueous media was decreased at elevated temperature. The
figures and tables indicated high uptake capacity (mg/g) of Pb2+
on the adsorbents at 303K. A
gradual decrease was inspected with the increase in temperature as indicated in the figure
4.60.The % removal of Pb2+
on the surfaces of RHC, KMRHC, RHA and KMRHA also
decreased gradually with the increase in temperature as shown in the figure 4.56. This revealed
that the adsorption of Pb2+
on the surfaces of RHC, KMRHC, RHA and KMRHA is exothermic
process. At high temperature the kinetic and vibrational energies of the adsorbents and
adsorbates are high which reduces the adsorbate/adsorbent interactions. It would also facilitate
the desorption of Pb2+
from the upper layers, adsorbed on the surface of adsorbents. The
multilayer formation on the surface of adsorbents has been confirmed by the Freundlich isotherm
as indicated from its high values of correlation factor (Table 4.73). It would also suggest that at
elevated temperature the adsorption of Pb2+
on the modified adsorbents turns into chemical from
physico-chemical adsorption. Hence temperature could affect the physical and chemical nature
of adsorption. The values of equilibrium constants and hence that of rate constants decreased at
high temperature as illustrated in the table 4.71, which indicated that the rate of adsorption
decreases at elevated temperature. Thus temperature could adversely affect the kinetics of
adsorption of Pb2+
.on the modified adsorbents. In other words we could say that the rate of
desorption increases at high temperature consequently, the rate of adsorption decreases. The
highest adsorption rate for all the modified adsorbents was investigated at 303K as indicated in
the table 4.71
180
Figure 4.60 Effect of‗ Temperature‘ on the Uptake Capacity (mg/g) of Pb
2+ on
RHC, KMRHC, RHA and KMRHA.
Figure 4.61 Effect of Temperature‘ on %.Adsorption of Pb
2+on RHC, KMRHC,
RHA and KMRHA
0
20
40
60
80
100
120
303 313 323 333 343
Up
take
Cap
acit
y (m
g/g)
Temperature (K)
RHC
KMRHC
RHA
KMRHA
0
20
40
60
80
100
120
300 310 320 330 340 350
%P
b2
+ A
dso
rbe
d
Temperature (K)
RHC
KMRHC
RHA
KMRHA
181
Table 4.67 Temperature Optimization Study for Adsorption of Pb2+
on Rice
Husk Char. Adsorbent-.Dose = 2g/L,Co = 250 mg/L, pH = 6, Agitation Time = 50min
Table 4.68 Temperature Optimization Study for Adsorption of Lead Ions on
KOH Modified Rice Husk Char. Adsorbent Dose = 2g/L, Co = 250 mg/L, pH = 6
Agitation Time = 50min
S. No Temp. (K)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 303 65.0 92.2 74.0
2 313 78.5 85.7 68.6
3 323 99.1 75.45 60.3
4 333 110.7 69.65 55.7
5 343 121.3 64.35 51.4
S. No Temp. (K)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 303 10.2 119.9 95.9
2 313 18.4 115.8 92.6
3 323 32.5 108.7 87.0
4 333 51.3 99.3 79.8
5 343 72.6 88.7 70.9
182
Table 4.69 Temperature Optimization Study for Adsorption of Pb2+
on RHA,
Adsorbent Dose = 2g/L, Co= 250 mg/L, pH = 6, Agitation Time = 80min
Table 4.70 Temperature Optimization Study for Adsorption of Pb2+
on
KMRHA, Adsorbent Dose = 2g/L, Co = 250 mg/L, pH = 6, Agitation Time = 70min.
S. No Temp. (K)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 303 76.5 86.75 69.4
2 313 82.0 84.0 67.2
3 323 93.4 78.3 62.6
4 333 109 70.5 56.4
5 343 123.8 63.1 50.4
S. No Temp. (K)
Conc. of
filtrate
Ce(mg/L)
Pb2+
adsorbed
qe (mg/g)
%Pb2+
adsorbed
1 303 22.6 113.7 90.9
2 313 27.6 111.2 88.9
3 323 51.3 99.3 79.8
4 333 83.7 83.2 66.7
5 343 99.5 75.25 60.02
183
4.9.6 ‗Thermodynamic Studies
The ‗thermodynamic studies of the adsorption‘ of Pb
2+ ions on RHC, KMRHC, RHA and
KMRHA adsorbents was explained on the basis of Gibbs free energy, which were calculated by
using equation (4.1),the equilibrium constant ‗K‘ was calculated using eq. (4.2) (section 4.7.6).
The values of ΔG were found negative for‘ adsorption of Pb2+
ions on RHC, KMRHC, RHA and
KMRHA as listed in table 4.71, which inferred for spontaneous process. The relationship
between free energy and temperature is given in eq. (4.3)(section 4.7.6). The plots of ΔGVs
Temperature are shown in figure 4.62. The values of ΔS and ΔH were computed from ‗slopes
and intercepts‘ of the plots respectively. ‗The thermodynamic parameters
‘ are listed in the table
4.71. The negative value of ΔH inferred for exothermic process. The negative values of ΔS
revealed that the adsorbate particles (Pb2+
) are localized on the surface of adsorbents and hence
the randomness decreased at the adsorbent/adsorbate interface.
Figure 4.62 ‗Plots of Free Energy
‘ Vs Temperature for the Adsorption of
Pb2+
on RHC, KMRHC, RHA and KMRHA-Adsorbents
y = 0.0629x - 21.649 R² = 0.9852
y = 0.1363x - 49.195 R² = 0.9988
y = 0.0517x - 17.915 R² = 0.9646
y = 0.128x - 44.943 R² = 0.9637 -9
-8
-7
-6
-5
-4
-3
-2
-1
0
300 320 340 360
ΔG
(K
j/m
ol)
Temperature (K)
Pb2+
RHC
KMRHC
RHA
KMRHA
184
Table 4.71 ‗Thermodynamic Parameters‘ for Adsorption of Pb
2+ on RHC, KMRHC, RHA
and KMRHA-Adsorbents
Temp.
(K)
ΔG (kJ/mol) Values of (K)
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
303 -2.619 -7.953 -2.062 -5.816 2.846 23.50 2.267 10.06
313 -2.029 -6.562 -1.866 -5.430 2.184 12.45 2.048 8.057
323 -1.127 -5.104 -1.385 -3.636 1.522 6.692 1.676 3.873
333 -0.636 -3.748 -0.712 -1.900 1.258 3.873 1.293 1.986
343 -0.168 -2.547 -0.054 -1.180 0.061 2.443 1.019 1.512
ΔH kJ/mol ΔS kj/mol/k
RHC KMRHC RHA KMRHA RHC KMRHC RHA KMRHA
-21.64 -49.19 -17.91 -44.94 -0.062 -0.136 -0.051 -0.128
4.9.7 ‗Adsorption Kinetics‘
Adsorption kinetics was studied for the investigation of rate and mechanism of the
removal of Pb2+
ions on RHC, KMRHC, RHA and KMRHA-adsorbents from aqueous media.
The pseudo.-first order‘ kinetics model is related to the physical interaction of the Pb
2+ ions and
adsorbent surface. Its nonlinear‘ and linear‘ forms are given in equations (4.4) and (4.5)
respectively. The chemical sorption of the Pb2+
ions on adsorbents was explained by Pseudo-
second order equation. Its nonlinear‘ and linear‘ forms are given in eq. (4.6) and (4.7) respectively
(section 4.7.7). Figures 4.63 and 4.64 indicated the plots of pseudo.-first and pseudo
.-second
order reactions respectively.
Values of both the rate constants, K1and K2., qe and R2 for the ‗adsorption‘ of Pb
2+ ions on
RHC, KMRHC, RHA and KMRHA-adsorbents were calculated from the plots given in the
185
figures 4.63 and 4.64, which are listed in the table 4.72. The R2values for pseudo
.-second order‘
model are greater than that of pseudo.-first order‘ model, also the values of qe, computed from
pseudo.-second order‘ kinetic model were agreed with the experimental ones which indicated that
this model is best fit to the kinetics data. It suggested that the adsorption of Pb2+
ions on RHC,
KMRHC, RHA and KMRHA-adsorbents is mostly chemical process (R. D. Zhang, et al., 2014).
Figure 4.63 Pseudo.-First Order
, Kinetic Model for‘ Adsorption of Pb
2+ on
RHC, KMRHC, RHA and KMRHA-Adsorbents
y = -0.0413x + 1.9035 R² = 0.9425
y = -0.034x + 1.734 R² = 0.9787
y = -0.0225x + 1.686 R² = 0.9923
y = -0.0147x + 1.7495 R² = 0.9925
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 10 20 30 40 50
Log(
qe−
qt)
Time (min)
Pb2+
RHC
KMRHC
RHA
KMRHA
186
Figure 4.64 Pseudo.-Second Order‘ Kinetic Model for Adsorption of Pb
2+ Ions
on RHC, KMRHC, RHA and KMRHA-Adsorbents
Table 4.72 The Numerical Values of ‗Rate Constants‘K1 andK2, qe andR
2for the Adsorption
of Pb2+
Ions on RHC, KMRHC, RHA and KMRHA-Adsorbents
Adsorbent
Pseudo.-first order‘ Pseudo
.-second order‘
K1.(min
-1). R
2. qe(mg/g).
K2.
.(g/mg.min) R
2. qe. (mg/g)
RHC 1.78×10-2
0.942 79.98 6.9×10-4
0.996 125
KMRHC 1.47×10-2
0.978 54.20 1.96×10-3
0.998 142.8
RHA 9.5×10-3
0.992 48.52 1.47×10-3
0.999 100
KMRHA 6.03×10-3
0.992 56.10 1.25×10-3
0.996 125
y = 0.0086x + 0.092 R² = 0.9969
y = 0.0079x + 0.0254 R² = 0.9985
y = 0.0108x + 0.0684 R² = 0.9992
y = 0.0089x + 0.0514 R² = 0.9967
0
0.1
0.2
0.3
0.4
0.5
0.6
0 10 20 30 40 50
t/ q
t
t (min)
Pb2+
RHC
KMRHC
RHA
KMRHA
187
4.9.8 Adsorption Isotherm Model
The linear form of Freundlich, Langmuir and Temkin models are given in eq. (4.8), (4.9)
and (4.10) or (4.11)(section 4.7.8).All the three models (Langmuir, Freundlich and Temkin) for‘
removal of Pb2+
from aqueous media on RHC, KMRHC, RHA and KMRHA-adsorbents are
depicted in the Figures 4.65, 4.66 and 4.67. The values of the parameters in these models are
listed in table 4.73.The equilibrium data was fit to all of the three isotherm models as indicated in
table 4.73.However the data is best fit to the Freundlich model which had the highest values of
R2
(0.938, 0.982, 0.951 and 0.991 for RHC, KMRHC, RHA and KMRHA-adsorbents
respectively). It assumed for multilayer coverage and physical-sorption. The other two models
could also be employed to explain the adsorption process. It has been found in the literature that
the experimental data could be fit to more than one model (Wang & Yan, 2011; Kumar, 2010).
The R2 value for Langmuir model is also high (R
2 = 0.986) for‘ adsorption of Pb
2+on KMRHA
which suggested for chemical adsorptions process. The R2 value for‘ Temkin model is greater
than 0.969 for‘ adsorption of Pb2+
ions on KMRHA which suggested for its heterogeneous
surface (Behnamfard, 2009). Hence the correlation factor R2 indicated that adsorption‘ of Pb
2+.
on KMRHA followed all the three models (Freundlich, Langmuir and Temkin).
188
Figure 4.65 Freundlich Isotherm for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA and
KMRHA from Aqueous Solution
189
Figure 4.66 Langmuir‘ Isotherms for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA, and
KMRHA from Aqueous Solution
190
Figure 4.67 Temkin Isotherms for‘ Adsorption of Pb2+
on RHC, KMRHC, RHA and KMRHA
from Aqueous Solution
191
Table4.73 Parameters in Langmuir‘, Freundlich. and Temkim Adsorption Isotherm
Models for‘ Adsorption of Pb2+.
on RHC, KMRHC, RHA and KMRHA from Aqueous
Solution
Adsorption
Isotherm
Model
Parameters RHC KMRHC RHA KMRHA
Langmuir
qm(mg/g) 125 166.6 142.8 200
KL.(L mg-1
) 0.0414 0.272 0.0205 0.0657
R2 0.873 0.974 0.85 0.986
Freundlich
n 2.785 2.985 2.036 1.742
KF(L mg-1
) 18.79 48.417 9.50 17.94
R2 0.938 0.982 0.951 0.991
Temkin
b (j/mol) 58.15 51.24 46.71 30.09
KTK (L/mg) 1.158 3.265 0.654 0.935
R2 0.808 0.882 0.853 0.969
192
4.10 Comparative Study
Adsorption of a representative dye Orange G (OG) was studied on the Rice Husk (source
material), thermally modified Rice Husk (RHC and RHA) and thermo-chemically modified Rice
Husk (KMRHC and KMRHA)under experimental conditions: Adsorbent dose =2g/L, C0 =
80mg/L, pH = 4 and temperature = 303K. Results of comparative study were demonstrated in the
figures 4.68 and 4.69, which indicated that the adsorption capacity (mg/g) and percent adsorption
of Rice Husk (RH) is very small as compare to the modified adsorbents. The figures indicated
that uptake capacity (mg/g) and %.adsorption of dye on Rice Husk was significantly improved
with thermal modification, which were further enhanced by the chemical modification. Hence
thermal and thermo-chemical modification of the source material (Rice Husk) could lead to
prepared adsorbents of ‗high efficiency‘ for the removal of toxic dyes and heavy metal ions from
aqueous media.
Figure 4.68 Comparative Study of Adsorption of Orange G Dye on RH, RHC,
RHA, KMRHC and KMRHA
0
5
10
15
20
25
30
35
40
10 20 30 40 50 60
qe
(m
g/g)
Time (min)
Comparative Study
RH
RHC
RHA
KMRHC
KMRHA
193
Figure 4.69 Comparative ‗Study of the Adsorption‘ of Orange G Dye on
RH, RHC, RHA, KMRHC and KMRHA
0
20
40
60
80
100
120
0 20 40 60 80
% O
G d
ye a
dso
rbe
d
Time (min)
Comparative study
RH
RHC
RHA
KMRHC
KMRHA
194
Conclusions
Different types of thermally and thermo-chemically modified adsorbents from locally
produced Rice Husk (RH) (low cost material) were successfully prepared.
An easy and economical method was developed for the chemical modification adsorbents
of high adsorption efficiencies.
KOH was employed for the chemical modification of adsorbents prepared from rice husk.
The KOH modified adsorbents were used for the adsorption of toxic dyes (OG and TY)
and heavy metal ions (Pb2+
) from aqueous media.
Results of the adsorption study indicated that the KOH modified adsorbents could
remove the toxic dyes (OG, TY) and Pb2+
ions from aqueous media almost completely at
dilute level.
The KOH modified Rice Husk Char could remove 96% OG dye from 80mg/L aqueous
solution, with adsorption capacity of 38.4 mg/g at 303K. The same adsorbent could
remove 95.9% Pb2+
ions from 250mg/L aqueous solution, with adsorption capacity of
119 mg/g at 303K.
The KOH modified Rice Husk Ash could remove 91.1% OG dye from 80mg/L aqueous
solution, with adsorption capacity of 36.45 mg/g at 303K. Whereas, it could remove
86.75% Pb2+
ions from 250mg/L of aqueous solution, with adsorption capacity of 113.7
mg/g at 303K.
Various adsorption isotherms such as Langmuir, Freundlich, and Temkin were employed
to the adsorption data and it was found that the data follow all the three isotherm models
in general, however, the values of correlation coefficients (R2) were found to vary with
varying the experimental conditions.
It was further found that adsorption efficiency, kinetics and thermodynamic behavior
were not only changing with the experimental conditions but also with the type of
adsorbent used.
We believed that the outcome of this study, which we are going to be published in the
journal of international repute, would provide guidelines for the industry people for the
production of chemically modified adsorbents on the commercial scale for wide range of
applications.
195
Future Recommendations
The adsorbents prepared via thermal and thermo-chemical process from the agricultural
waste product, Rice Husk, would provide guide lines for the researchers to prepare modified and
functionalized adsorbents from RH that would have high adsorption capability and economical
values. Though the thermal and KOH modified adsorbent prepared from rice husk have high
adsorption efficiencies, yet their preparation requires energy hence the RH is need to be
functionalized with specific functional groups to solve the economical task and to enhance its
marketing values. Selective adsorption of cationic and anionic dyes is the research task of the
day, which could be solved to prepared functional materials from RH through specific functional
groups. Furthermore, the % adsorption capability for contaminants, of the prepared adsorbents in
this work is high in very dilute solutions, Hence further research is needed to prepared activated
adsorbents from RH, that have high %adsorption efficiency for highly concentrated solutions of
dyes and heavy metal ions.
196
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List of Publications
HAQ, I. U., AKHTAR, K. & MALIK, A. 2014. Effect of experimental variables on the
extraction of silica from the rice husk ash. J. Chem. Soc. Pak, 36, 382.
AKHTAR, K., KHALID, H., HAQ, I. U. & MALIK, A. 2016. Improvement in tribological
properties of lubricating grease with quartz-enriched rice husk ash. Tribology
International, 93, 58-62.
MALIK, A., KHAN, A. & HUMAYUN, M. 2018. Preparation and Chemical Modification of
Rice Husk Char for the Removal of a Toxic Dye (Orange G) from Aqueous Medium.
Zeitschrift für Physikalische Chemie. DOI: https://doi.org/10.1515/zpch-2018-1190
KHAN, M., TIEHU, L., ZHAO, T. K., ALI, Z., MALIK, A., KHAN, A., KHAN, I., ULLAH,
A., JIAO, S., IDREES, M., XIONG, C. 2017. Effects of multi walled carbon
nanotubes and nanodiamond particles on the properties of pitch derived carbon foam
composites. Diamond & Related Materials. DOI: doi: 10.1016/j.diamond.2017.09.008
MALIK, A., KHAN, A., ANWAR, N., & NAEEM, M. 2018.Comparative Study of the
Adsorption of Congo red Dye on Rice Husk (RH), Rice Husk Char (RHC) and
Chemically Modified Rice Husk Char (CMRHC) from Aqueous Media.( Korean
Journal of Chemical Engineering) (Submitted for Publication to Bulitin of The
Chemical Society Ethopia & under Review).
MALIK, A., KHAN, A., KHAN, G. S. & SHAH, L. A. 2018. Thermo-chemical modification of
Rice Husk for the removal Pb2+
from aqueous medium. (Submitted for Publication to
Chinese Journal of Chemical Physics & under Review).
MALIK, A., KHAN, A. 2018. Enhancement of the adsorption efficiency of rice husk ash by
chemical modification for the removal of crystal violet dye from aqueous media.
(Submitted for Publication to Journal of the Chilean Chemical Society & Under
Review).
MALIK, A., KHAN, A., 2019. Removal of Direct Blue (DB) and Titan Yellow (TY) dyes from
aqueous media using KOH Modified Rice Husk Char (KMRHC).(Submitted for
Publication to Russian Chemical Bulitin & under Review).
226
MALIK, A., KHAN, A. 2019. Enhancement of the sorption capacity of MS-adsorbent by Silica
enriched Rice Husk Ash for the removal of Congo red dye from aqueous
media).(under prepration).
MALIK, A., KHAN, A. 2019. Comparative study for the removal direct blue dye by Rice Husk
Char and Chemically Modified Rice Husk Char.(under prepration).
MALIK, A., KHAN, A. 2019. Removal of toxic dyes (Crystal Violet and Orange G) from
aqueous media by KOH Modified Rice Husk Ash (KMRHA).(under prepration).
(NOTE: The front pages of the published papers are hereby attached with the thesis)
