SYNTHESIS, CHARACTERIZATION AND SORPTION PROPERTIES OF

MICROPOROUS TITANOSILICATE ETS-10 FROM RICE HUSK ASH

JEI CHING YIH

UNIVERSITI TEKNOLOGI MALAYSIA

iii

To my love one

Wong Hon Loong

To my beloved parents

Jei Mok Choon and Wong Mai Yin

To my beloved brother and sister

Jei Jenn Ning and Jei Chien Fong

For their love that made me firm and resolute

iv

ACKNOWLEDGEMENTS

I am eternally grateful to many individuals for the education, knowledge and

experience that I gained over the past two years. First of all, I would like to express

my sincere appreciation to my project supervisor, Associate Professor Dr. Mustaffa

Shamsuddin for giving me the opportunity to carry out research in the fascinating

area of microporous molecular sieves and zeolites. Besides, I also would like to

thank my project co-supervisor, Associate Professor Dr. Azli Sulaiman for his

professional advice and emotional support. I thank for their helpful suggestion,

direction, advice and sympathetic guidance during the entire course of this research.

I would like to thank all the staffs from the Department of Chemistry and

Ibnu Sina Institute for Fundamental Science Studies, UTM for their prompt and

timely help during my study and research. Grateful acknowledge to the Ministry of

Science, Technology and Innovation (MOSTI) Malaysia for its financial support

through research grant, IRPA funding 09-02-06-0057-SR005/09-05 (Vot 74509). I

also would like to thank Universiti Teknologi Malaysia for offering a UTM-PTP

research scholarship.

I am also deeply grateful to everyone who has encouraged me and assisted

me in completing this research. Next, I would also thank my labmates and

housemates. They are so kind and always willing to share their experience and

knowledge with me.

Last but not least, I would like to send my deepest appreciation to my family

and my love one. They are always there to help us when I am facing problems and

give me supporting at all times.

v

PREFACE

This thesis is the result of my work carried out in the Department of Chemistry;

Universiti Teknologi Malaysia between July 2005 to December 2006 under

supervision of Assoc. Prof. Dr. Mustaffa Shamsuddin. Part of my work described in

this thesis has been reported in the following publications or presentations:

1. Jei, C. Y., Sulaiman, A. and Shamsuddin, M. Synthesis and Characterization

of Microporous Titanosilicate, ETS-10 from Agricultural Waste. Proceeding

of 1st Penang International Conference of Young Chemists. Universiti Sains

Malaysia. 2006.

2. Jei, C. Y., Sulaiman, A. and Shamsuddin, M. Physicochemistry Analysis of

ETS-10 Derived from Rice Husk Ash. Poster presentation at the 19th

Simposium Kimia Analisis Malaysia (SKAM-18). Universiti Teknologi

Malaysia, 2006.

vi

ABSTRACT

A new class of nano-sized microporous titanosilicate ETS-10 has been

prepared through hydrothermal synthesis route in the absence of ETS-4 and organic

template agent. Local agriculture waste – rice husk ash (RHA) has been used as the

silica source and commercial titanium oxide namely P25 as titanium source. For

comparison, the colloidal silica source, LUDOX-30 was also used as a silica source

to synthesize the ETS-10. The influence of some synthesis parameters such as

synthesis time and heating temperature on the crystallization of ETS-10 and the gel

oxides composition have also been investigated. The physico-chemical

characterization of these synthesized materials have been carried out by X-ray

Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), UV-Vis

spectroscopy (UV-VIS), Field Emission Scanning Electron Microscopy (FESEM),

Solid State Nuclear Magnetic Resonance (NMR), nitrogen adsorption-desorption

analysis and Raman spectroscopy. The best ETS-10 sample was successfully

obtained under heating at 220°C for 52 hours using the following molar ratio TiO2 :

3.75SiO2 : 1.5NaOH : 0.54KF : 21.25H2O. The ability of the synthesized ETS-10 as

adsorbents for heavy metal ion such as Pb2+, Cd2+ and Cu2+ was investigated. The

study of equilibrium and adsorption isotherm at 298 K was conducted using batch

mode. The uptake rates for these heavy metal ions were extremely fast and fitted well

with the pseudo-second order model and Langmuir equation with an affinity order of

Pb2+ > Cd2+ > Cu2+, with values of 1.86, 1.51 and 1.45 mmol/g respectively, which

are the highest adsorptive capacities of the heavy metal ions on zeolite materials

reported so far. This indicates that ETS-10 is a very promising adsorbent for divalent

heavy metals.

vii

ABSTRAK

Titanosilikat ETS-10 mikroliang bersaiz nano telah disintesis melalui tindak

balas hidroterma tanpa ETS-4 sebagai benih dan agen organik. Abu sekam padi yang

merupakan sisa buangan pertanian tempatan telah digunakan sebagai sumber silika

dan titanium oksida komersil (P25) digunakan sebagai sumber titanium. Untuk

tujuan perbandingan, silika koloid (LUDOX-30) juga digunakan sebagai sumber

silika dalam sintesis ETS-10. Parameter yang mempengaruhi proses sintesis ETS-10

dan komposisi oksida gelnya seperti masa dan suhu tindak balas juga dikaji. Hasil

daripada sintesis telah dicirikan menggunakan pembelauan sinar-X (XRD),

spektroskopi infra-merah transformasi Fourier (FT-IR), spektrokopi ultra

lembayung-nampak (UV-VIS), mikroskopi elektron imbasan pancaran medan

(FESEM), spekstroskopi resonans magnet nuklear keadaan pepejal (RMN), analisis

penjerapan dan penyahjerapan nitrogen and spektroskopi Raman. Sampel ETS-10

yang paling tulen didapatkan dengan menggunakan nisbah molar TiO2 : 3.75SiO2 :

1.5NaOH : 0.54KF : 21.25H2O pada suhu 220°C selama 52 jam. Sampel ETS-10

tulen ini kemudiannya digunakan dalam proses penjerapan untuk tujuan

penyingkiran ion logam berat, terutamanya Pb2+, Cd2+ dan Cu2+. Dalam kajian ini,

keseimbangan dan penjerapan isoterma pada suhu 25°C telah dijalankan melalui

kaedah berkelompok. Kadar penjerapan untuk logam berat tersebut sangat pantas dan

mematuhi dengan baik model pseudo tertib kedua dan model isoterma Langmuir

dengan urutan Pb2+ > Cd2+ > Cu2+ dengan nilai keupayaan penjerapan 1.86, 1.51 and

1.45 mmol/g masing-masing yang merupakan muatan penjerapan paling tinggi

berbanding dengan zeolit lain yang dilaporkan setakat ini. Ini membuktikan bahawa

ETS-10 adalah penjerap yang paling berpotensi terutamanya untuk penjerapan logam

berat dwivalen.

viii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

PREFACE v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF TABLES xii

LIST OF FIGURES xv

LIST OF SYMBOLS xxi

LIST OF ABBREVIATIONS xxii

LIST OF APPENDICIES xxiii

1 INTRODUCTION

1.1 Research Background 1

1.2 Scope of Study 4

1.3 Objective of Study 5

2 LITERATURE REVIEW

2.1 Techniques for Heavy Metals Uptake from

Contaminated Water

6

2.1.1 Chemical Precipitation Method 7

2.1.2 Coagulation Method 7

ix

2.1.3 Electrodialysis Method 7

2.1.4 Ultrafiltration Method 8

2.1.5 Reverse Osmosis Method 8

2.1.6 Adsorption Method 8

2.1.7 Ion Exchange Method 9

2.2 Microporous Titanosilicate 10

2.3 Microporous Titanosilicate – ETS-10

2.3.1 Synthesis of ETS-10 13

2.3.2 Properties of ETS-10 16

2.3.2.1 Catalysis 16

2.3.2.2 Optical Properties 18

2.3.2.3 Adsorption and Ion-exchange Capability

19

3 EXPERIMENTAL

3.1 Synthesis of Microporous Titanosilicate, ETS-10 22

3.2 Modification of ETS-10

3.2.1 Desilication 23

3.2.2 Ion Exchange with Sodium, Potassium or Proton Ions

24

3.3 Synthesis of Zeolite 25

3.3.1 Synthesis of Zeolite A, X and Y 25

3.4 Characterization of ETS-10 Samples 26

3.4.1 X-ray Powder Diffraction (XRD) 26

3.4.2 Fourier Transform Infrared Spectroscopy (FTIR)

27

3.4.3 Raman Spectroscopy 27

3.4.4 Diffuse Reflectance Ultraviolet-visible Spectroscopy ( DR UV-vis)

27

3.4.5 Field Emission Scanning Electron Microscopy (FE-SEM)

28

3.4.6 EDAX Elemental Analysis 28

3.4.7 Solid State Nuclear Magnetic Resonance (NMR)

28

3.4.8 BET Surface Area Analysis 29

x

3.4.9 Measurement of Cation Exchange Capacity (CEC)

29

3.4.10 Flame Atomic Absorption Spectroscopy (FAAS)

30

3.5 Batch-Type Sorption Method 31

3.5.1 Sorption Study on Single Metal Ion Systems 31

3.5.1.1 Kinetic Studies 32

3.5.1.2 Effect of Initial pH 32

3.5.1.3 Adsorption Isotherm Studies 33

3.5.2 Sorption Study on Binary and Ternary Metal Ion System

34

3.5.2.1 Kinetic Studies 34

3.5.2.2 Adsorption Isotherm Studies 35

4 RESULTS AND DISCUSSION

4.1 Synthesis of ETS-10

4.1.1 The Effect of Different Ti Sources 36

4.1.2 The Effect of Different Silica Source 39

4.1.3 Influence of the Crystallization Time 40

4.1.4 The Effect of Different Molar Ratio 42

4.2 Characterization of Synthesized ETS-10

4.2.1 Fourier Transform Infrared Spectroscopy (FTIR)

45

4.2.2 Raman Spectroscopy 46

4.2.3 Diffuse Reflectance Ultraviolet-visible Spectroscopy (UV-vis)

48

4.2.4 Field Emission Scanning Electron Microscopy (FESEM)

49

4.2.5 Solid State Nuclear Magnetic Resonance (NMR)

51

4.2.6 BET Surface Area Analysis 54

4.3 Characterization of RHA Synthesized Zeolite A, X, Y 55

4.4 Modification of ETS-10

4.4.1 Desilication 56

4.4.2 Ion Exchange with Sodium, Potassium or Proton Ions

62

xi

4.5 Determination of Cation Exchange Capacity 67

4.6 Sorption Study on Single Metal Ion Systems

4.6.1 Kinetic Study 69

4.6.2 Effect of Initial pH 72

4.6.3 Adsorption Isotherm Studies 73

4.7 Sorption Study on Binary and Ternary Metal Ion System

81

4.7.1 Kinetic Studies 81

4.7.2 Adsorption Isotherm Studies 85

5 CONCLUSIONS AND SUGGESTIONS

5.1 Conclusion 89

5.2 Suggestions 91

REFERENCES 92

Appendices A - C 106

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 The different reactants molar ratio used for ETS-10 synthesis 23

3.2 The molar ratio, heating temperature and crystallization

period which used for zeolite A, X and Y synthesis 25

3.3 Operating parameters of FAAS in the measurement of the

desired elements 30

3.4 Metal solution used for the sorption kinetic studies 34

4.1 The phases of the final products synthesized using different

Ti sources 38

4.2 The effects of different crystallization time and silica

sources at 220°C towards the ETS-10 synthesis and its

comparative relative crystallinity 41

4.3 The final products synthesized from different molar ratio at

220°C and its comparative relative crystallinity 44

4.4 FTIR spectral data of ETS-10 and the type of vibrations

generating the peaks 46

4.5 The Raman adsorption spectral data of ETS-10 and the type

of vibrations generating the peaks 47

xiii

4.6 The EDAX elementals analytical data for the ETS-10 51

4.7 The chemical shift for LUDOX and RHA synthesized ETS-10 52

4.8 The BET surface area for LUDOX and RHA synthesized

ETS-10 55

4.9 The Raman adsorption spectral data of desilication ETS-10

and the type of vibrations generating the peaks 59

4.10 The CEC and percent of comparative relative crystallinity

for desilicated ETS-10 at different temperature 61

4.11 The CEC and percent of comparative relative crystallinity

for desilicated ETS-10 at different stirring period 61

4.12 The CEC and percent of comparative relative crystallinity

for desilicated ETS-10 at different concentration of sodium

carbonate 62

4.13 The BET surface area for ion exchanged ETS-10 63

4.14 The CEC for Ludox and RHA synthesized ETS-10 at

different time, ion-exchanged ETS-10 and zeolite A, X and

Y 68

4.15 The pseudo-second-order rate constant (k2), correlation

coefficient (r2) and uptake equilibrium (qe) values for the

RHA synthesized ETS-10 in the removal of Pb2+, Cd2+ and

Cu2+ 71

4.16 Some physical parameters of heavy metal ions in solution

[109] 75

xiv

4.17 The Langmuir and Freundlich isotherm parameters of Pb2+,

Cd2+ and Cu2+ on Ludox synthesized ETS-10 (LETS-10)

and RHA synthesized ETS-10 (RETS-10) at pH 5 and 25°C 76

4.18 The Langmuir and Freundlich isotherm parameters of Pb2+,

Cd2+ and Cu2+ on RHA synthesized ETS-10 (RETS-10) and

zeolite A, X and Y at pH 5 and 25°C 80

4.19 The pseudo-second-order rate constant (k2), uptake

equilibrium (qe) values and correlation coefficient (r2) for

the RETS-10 in Pb2+−Cd2+, Pb2+−Cu2+, Cd2+−Cu2+ and

Pb2+−Cu2+−Cd2+ systems 84

4.20 The Langmuir isotherm parameters of Pb2+ and Cd2+ for the

RETS-10 in Pb2+−Cd2+, Pb2+−Cu2+, Cd2+−Cu2+ and

Pb2+−Cu2+−Cd2+ systems 85

xv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 The structure of (a) ETS-4 [36] and (b) ETS-10 [37] 11

2.2 The ETS-10 structure arrangement where the red colour

represents the SiO4 and the blue colour represents the TiO6 12

2.3 The framework structure of ETS-10 showing chains of

corner-sharing TiO6 octahedra which run along two

perpendicular directions, and which are isolated by corner-

sharing SiO4 tetrahedra: (a) single element of the chain;

(b) single TiO6 chain; (c) three dimensional view. For

clarity, extra framework (charge-balancing) cations were

omitted 19

4.1 XRD pattern of the ETS-10 sample synthesized from

commercial anatase TiO2 at 200°C (a) commercial anatase

TiO2, (b) crystallization at 48 hours, (c) crystallization at 52

hours and (d) crystallization at 72 hours. A indicates

unreacted anatase and Q represents quartz 37

4.2 XRD pattern of the ETS-10 sample synthesized from P25 at

200°C (a) P25, (b) crystallization at 48 hours,

(c) crystallization at 52 hours and (d) crystallization at 72

hours. A indicates unreacted P25 37

xvi

4.3 XRD pattern of the ETS-10 sample synthesized from P25

at 220°C (a) P25 and (b) crystallization at 52 hours 38

4.4 XRD pattern of the ETS-10 samples synthesized from

Ludox-30 at 220°C (a) crystallization at 48 hours, (b)

crystallization at 52 hours and (c) crystallization at 72

hours. A indicates unreacted P25 and asterisk indicates the

ETS-4 impurities 39

4.5 XRD pattern of the ETS-10 samples synthesized from RHA

at 220°C (a) crystallization at 48 hours, (b) crystallization at

52 hours and (c) crystallization at 72 hours 40

4.6 XRD pattern of the ETS-10 (1) samples synthesized using

batch 1 molar ratio (TiO2 : 5SiO2 : 3NaOH : 0.75KF :

94.5H2O) at 220°C (a) crystallization at 48 hours, (b)

crystallization at 52 hours and (c) crystallization at 72 hours 42

4.7 XRD pattern of the ETS-10 (2) samples synthesized using

batch 2 molar ratio (TiO2 : 3.75SiO2 : 1.5NaOH : 0.54KF :

21.25H2O) at 220°C (a) crystallization at 48 hours, (b)

crystallization at 52 hours and (c) crystallization at 72 hours 43

4.8 XRD pattern of the ETS-10 (3) samples synthesized using

batch 3 molar ratio (TiO2 : 5.5SiO2 : 3.4Na2O : 1.5K2O :

180H2O) at 220°C (a) crystallization at 48 hours,

(b) crystallization at 52 hours and (c) crystallization at 72

hours 43

4.9 FTIR spectra (a) ETS-10 synthesis from RHA and

(b) ETS-10 synthesis from Ludox 45

4.10 Raman spectra (a) ETS-10 synthesis from RHA and

(b) ETS-10 synthesis from Ludox 47

xvii

4.11 Diffuse reflectance UV-Vis spectra for ETS-10 48

4.12 FESEM for ETS-10 that are synthesized using Ludox at

220°C (a) 48 hours, (b) 52 hours and (c) 72 hours 50

4.13 FESEM for ETS-10 that are synthesized using RHA at

220°C (a) 48 hours, (b) 52 hours and (c) 72 hours 50

4.14 The EDAX spectrum for the ETS-10 synthesized using

RHA at 52 hours crystallization time at 220°C 51

4.15 The MAS 29Si NMR spectra for the LUDOX synthesized

ETS-10 at 220°C for (a) 48 hours, (b) 52 hours and (c) 72

hours. Asterisks indicate the AM-3 impurities 53

4.16 The MAS 29Si NMR spectra for the RHA synthesized ETS-

10 at 220°C for (a) 48 hours, (b) 52 hours and (c) 72 hours.

Asterisk indicates the AM-3 impurity 54

4.17 XRD patterns for the RHA synthesized zeolites

(a) Zeolite A, (b) Zeolite X and (c) Zeolite Y 56

4.18 XRD pattern of the desilicated ETS-10 samples at different

temperature (a) 27°C, (b) 40°C, (c) 50°C, (d) 60°C, (e)

70°C, (f) 80°C, (g) 90°C and (h) 100°C 57

4.19 XRD pattern of the desilicated ETS-10 samples at different

temperature (a)1 hour, (b) 2 hours, (c) 3 hours, (d) 4 hours,

(e) 5 hours and (f) 6 hours 58

4.20 XRD pattern of the desilicated ETS-10 samples at different

temperature (a)0.05 M, (b) 0.1 M, (c) 0.2 M, (d) 0.4 M, (e)

0.6 M, (f) 0.8 M and (g) 1 M 58

xviii

4.21 Raman spectra for desilicated ETS-10 59

4.22 The FESEM micrograph of desilicated ETS-10 60

4.23 The MAS 29Si NMR spectrum of the desilicated ETS-10 60

4.24 The XRD patterns for (a) Na-exchanged ETS-10,

(b) K-exchanged ETS-10 and (c) protonated ETS-10 63

4.25 The FESEM micrographs for (a) Na-exchanged ETS-10,

(b) K-exchanged ETS-10 and (c) protonated ETS-10 64

4.26 The MAS 29Si NMR spectra for (a) Na-exchanged ETS-10,

(b) K-exchanged ETS-10 and (c) protonated ETS-10.

Asterisk indicates the AM-3 impurity while Q3 and Q4

indicate the Q3 and Q4 silicon signals 65

4.27 The uptake kinetic of Pb2+, Cd2+ and Cu2+ on ETS-10 at

25°C using the initial concentration of 8 mmol/L and batch

factor of 200 mL/g 69

4.28 Pseudo-second-order sorption kinetics of Pb2+, Cd2+ and

Cu2+ onto ETS-10 71

4.29 The effect of pH on the uptake capacity of Pb2+, Cd2+ and

Cu2+ on ETS-10 at 25°C using the initial concentration of

8 mmol/L and batch factor of 200 mL/g 72

4.30 The uptake isotherms of Pb2+, Cd2+ and Cu2+ on RHA

synthesized ETS-10 at pH 5 and 25°C 73

4.31 The uptake isotherms of Pb2+, Cd2+ and Cu2+ on Ludox

synthesized ETS-10 at pH 5 and 25°C 74

xix

4.32 The adsorption isotherms of Pb2+ on RHA synthesized

ETS-10 and zeolite A, X and Y at pH 5 and 25°C 77

4.33 The adsorption isotherms of Cd2+ ions on RHA synthesized

ETS-10 and zeolite A, X and Y at pH 5 and 25°C 78

4.34 The adsorption isotherms of Cu2+ on RHA synthesized

ETS-10 and zeolite A, X and Y at pH 5 and 25°C 78

4.35 The competitive adsorption kinetics in Pb2+−Cd2+ system

on RETS-10 at 25°C using the initial concentration of 10

mmol/L and batch factor of 200 mL/g 82

4.36 The competitive adsorption kinetics in Pb2+−Cu2+ system

on RETS-10 at 25°C using the initial concentration of 10

mmol/L and batch factor of 200 mL/g 82

4.37 The competitive adsorption kinetics in Cd2+−Cu2+ system

on RETS-10 at 25°C using the initial concentration of

10 mmol/L and batch factor of 200 mL/g 83

4.38 The competitive adsorption kinetics in Pb2+−Cd2+−Cu2+

system on RETS-10 at 25°C using the initial concentration

of 10 mmol/L and batch factor of 200 mL/g 83

4.39 The competitive adsorption isotherm in Pb2+−Cd2+ system

on RETS-10 at 25°C using the initial concentration of 10

mmol/L and batch factor of 200 mL/g 86

4.40 The competitive adsorption isotherm in Pb2+−Cu2+ system

on RETS-10 at 25°C using the initial concentration of 10

mmol/L and batch factor of 200 mL/g 86

xx

4.41 The competitive adsorption isotherm in Cd2+−Cu2+ system

on RETS-10 at 25°C using the initial concentration of 10

mmol/L and batch factor of 200 mL/g 87

4.42 The competitive adsorption isotherm in Pb2+−Cd2+−Cu2+

system on RETS-10 at 25°C using the initial concentration

of 10 mmol/L and batch factor of 200 mL/g 87

xxi

LIST OF SYMBOLS

°C - Degree Celsius

Co - Initial concentration

Ce - Equilibrium concentration

cm - Centi meter

g - Gram

kg - Kilo gram

kV - Kilo Volt

L - Liter

m - Meter

M - Molar

meq - Mili equivalent

mg - Mili gram

MHz - Mega Hertz

mL - Mili Liter

mm - Mili meter

mmol - Mili mol

mW - Mili Watt

N - Normal

nm - Nano meter

ppm - Part per million

Å - Angstrom

µL - Micro Liter

µm - Micro meter

λ - Lambda

δ - Delta

θ - Theta

xxii

LIST OF ABBREVIATIONS

ETS-4 - Engelhard titanosilicate-4

ETS-10 - Engelhard titanosilicate-10

AAS - Atomic Absorption Spectroscopy

BET - Brunauer, Emmet, and Teller

CEC - Cation Exchange Capacity

FAAS - Flame Atomic Absorption Spectroscopy

FAU - Faujasite

FESEM - Field Emission Scanning Electron Microscopy

FTIR - Fourier Transform Infrared

h - Hour

ICP-MS - Inductively Coupled Plasma Mass Spectrometry

FTIR - Fourier Transform Infrared

NMR - Nuclear Magnetic Resonance

RHA - Rice Husk Ash

rpm - Revolution per minute

TEACl - Tetraethylammonium chloride

TMACl - Tetramethylammonium chloride

UV-Vis - Ultra Violet-Visible

XPS - X-ray photoelectron spectroscopy

XRD - X-Ray Diffraction

XRF - X-Ray Flourescence

V - Volume

xxiii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A FAAS Standard Calibration Curve for Lead

(Pb)

106

B FAAS Standard Calibration Curve for

Cadmium (Cd)

107

C FAAS Standard Calibration Curve for Copper

(Cu)

108

1

CHAPTER 1

INTRODUCTION

1.1 Research background

Due to the modern life nowadays, a lot of new technologies bring us to the

easier life but at the same time it also brings the worst effects to the environment.

Heavy metals such as lead (Pb), copper (Cu) and cadmium (Cd) which are released

into aquatic environments largely from various anthropogenic activities are serious

concern for human health and the environment. Therefore, removal of the heavy

metal pollutants from aqueous systems has received a considerable amount of

attention in order to control wastewater into an acceptable level according to the

environmental regulations worldwide.

There are many water treatment processes such as chemical precipitation [1],

adsorption [2], reverse osmosis [3], electro-dialysis [4], ultra-filtration [5,6] and ion-

exchange [7,8] that are currently available for removal of heavy metals. Among them,

the sorption process including ion-exchange and adsorption are the attractive ones,

due to their relatively simple and safe process. Ion exchange for cation removal is

often competitive with the classical chemical methods as it exhibits good

performances, reasonable costs and sometimes metal recovery ability [9]. Hence, the

good performances adsorbent has been investigated widely for this purpose.

Since its first introduction for heavy metal removal, it is undoubted that

activated carbon has been the most and widely used adsorbent in wastewater

2

treatment applications throughout the world. In spite of its prolific use, activated

carbon remains an expensive material since higher the quality of the activated carbon,

the higher it cost. Therefore, this situation makes it no longer attractive to be widely

used in the small-scale industries due to cost inefficiency. Until currently, there are

still many researchers working on inexpensive materials in search of the low-cost

adsorbents for heavy metal removal. As a result, the low-cost adsorbents which have

high adsorption capacity and locally available are desired. It is evident from the

literature survey of about 100 papers that low-cost adsorbents have demonstrated

outstanding removal capabilities for certain metal ions as compared to activated

carbon [10].

In the past few decades, both natural and synthetic zeolites have been studied

for heavy metal removal [11]. With increasingly stringent environmental regulations

for heavy metal presence in drinking water and wastewater, novel zeolite ion

exchangers with fast ion exchange rates and high uptake capacities are desired.

Natural zeolites gained a significant interest among scientists due to their ion-

exchange capability to preferentially remove unwanted heavy metals such as

strontium and cesium [10]. This unique property makes zeolites favourable for

wastewater treatment. However, the abundance of natural zeolites, an unavoidable

problem of the utilization is the coexistence of the considerable impurities within the

zeolitic tuffs, which interferes the exchange behavior of natural zeolites with heavy

metals. As a result, synthetic zeolites which usually posses higher exchange capacity,

easily controlled and known physico-chemical properties relative to that natural

zeolites, have been preferred [12].

Currently many researches are being carried out on the synthesis of zeolite or

microporous and mesoporous materials for the better heavy metal removal. In 1989,

a new class of microporous titanosilicate molecular sieves zeolite with octahedral

coordinated titanium framework known as (Engelhard Titanosilicate-4), ETS-4 with

pore size 0.3 – 0.4 nm and ETS-10 with pore size 0.49 – 0.76 nm were discovered by

Kuznicki [13-15]. This new family of microporous titanosilicates have been shown

to possess zeolite-like properties such as catalysis, separation, absorption and ion

exchange [16].

3

The ETS-10 comprises of corner-sharing [SiO4]4- tetrahedra and [TiO6]8-

octahedra linked through oxygen atoms, forming a three-dimensional 12-membered

ring network with pore-opening size of about 0.8 nm [17]. In ETS-10 the titanium

(IV) is found in the centre of the corner-sharing octahedral and the silicon in the

centre of corner sharing tetrahedral. This produces an anionic framework whereby,

whenever titanium is present in the structure, there is an associated two minus charge

which is compensated by extra-framework cations (Na+ and K+ in as-synthesised

ETS-10) [18]. Such a unique framework property has been demonstrated to display

unusual adsorption properties towards heavy metal ions in aqueous solution [19].

Unlike conventional aluminosilicate zeolites which are chemically constituted from

SiO4 and AlO4 tetrahedrals giving rise to one negative charge for each AlO4

tetrahedron balanced by an ion-exchangeable cation like Na+. Therefore the

associated two minus charge in ETS-10 structure make it a very interesting and

suitable material for extremely fast ion exchange especially for divalent heavy metal

cations removal compared with the zeolites which only has one minus charge in the

structure.

Since the first report of ETS-10, many titanium sources have been used to

synthesize ETS-10. TiCl3 was used as the Ti source in the initial report of synthesis

of ETS-10 by Kuznicki [13]. Due to the relatively expensive of TiCl3, the search for

alternative Ti source had been carried out. Thus, organotitanium compounds, TiCl4

and TiF4 had been used as Ti precursor to prepare ETS-10. However, the commercial

pure anatase TiO2 and commercial nano-sized TiO2 (commercially known as P25) is

of particular interest for the synthesis of ETS-10 because they are commercially

readily available and do not bring any unwanted guest anions like Cl- and F-.

Silica is one of the basic raw materials in synthesizing ETS-10. Many

researchers have used Ludox to synthesize the ETS-10. At present, there is still no

report of the rice husk ash being used as silica source to synthesize the ETS-10.

Since the rice husk is an agricultural waste material and locally available with high

percentage of silica, it becomes very suitable for low cost ETS-10 production. These

advantages make it an important material for water purification process, especially in

drinking water and waste water treatment. This will lead to an improved water

quality for healthier life and green environment in Malaysia.

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1.2 Scope of Study

In the research, the synthesis of ETS-10 was carried out using locally

produced rice husk ash as the silica source and titanium dioxide (namely P25) as the

titanium source in different molar oxide gel ratio. During the synthesis of ETS-10,

optimisation of the experimental conditions such as pressure, heating temperature,

pH, duration of stirring and reaction time were investigated. The structure and of the

synthesized ETS-10 from rice husk ash will be compared with the ETS-10

synthesized from colloidal silica source, LUDOX-30.

Modification of the ETS-10, will also be carried out where a novel method

called desilication will be applied to the synthesized ETS-10. In this method, some

silicon will be selectively removed from the ETS-10 framework in order to create an

extra ion exchange capacity. The desilication process toward ETS-10 will be

optimized systematically by altering the temperature, time and concentration of the

modifier. The original ETS-10 and desilicated ETS-10 will then be modified with

NaNO3, KNO3 and NH4NO3 to produce the sodium, potassium loaded ETS-10 and

protonated ETS-10 in order to use it as an ion-exchanger.

All the synthesized ETS-10, desilicated ETS-10 and modified ETS-10 were

characterized by Fourier transform infrared spectroscopy (FTIR), Raman

spectroscopy, UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), solid state

nuclear magnetic resonance (NMR), field emission scanning electron microscopy

(FESEM), thermogravimetric analysis and simultaneous differential thermal analysis

(TG-SDTA), nitrogen adsorption-desorption study for surface area analysis and

cation exchange capacity for the ion-exchange capacity analysis (CEC).

The sorption properties of the RHA synthesized ETS-10 were tested using

water samples containing toxic heavy metals such as Pb2+, Cd2+ and Cu2+ under

single, binary or ternary systems. The selectivity, kinetics and equilibrium, efficiency

and ion exchange capacity of the ETS-10 were determined by Flame Atomic

Absorption Spectroscopy (FAAS).

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For comparison purpose, the LUDOX synthesized ETS-10 and RHA

synthesized zeolite such as Zeolite A, Zeolite X and Zeolite Y samples were tested

using water samples containing toxic heavy metals such as Pb2+, Cd2+ and Cu2+ under

single metal ion system. The selectivity, kinetics and equilibrium, efficiency and ion

exchange capacity of this LUDOX synthesized ETS-10 and zeolite will be

determined by Flame Atomic Absorption Spectroscopy (FAAS).

1.3 Objective of Study

(i) To synthesize the microporous titanosilicate 10 (ETS-10) using rice husk ash

as a silica source.

(ii) To modify the synthesized ETS-10 by desilication and ion-exchange methods.

(iii) To characterize the physico-chemical properties of the synthesized and

modified ETS-10.

(iv) To study the sorption properties of the synthesized and modified ETS-10 as

an ion exchanger for Pb2+, Cd2+ or Cu2+ in aqueous samples.

(v) To compare the sorption properties of ETS-10 and zeolite under single metal

ion system toward the removal of Pb2+, Cd2+ or Cu2+ in the aqueous samples.