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TREATMENT OF ORGANIC WASTE WATER
USING GRAPHENE & GRAPHENE OXIDE
PROJECT THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF CHEMICAL
ENGINEERING OF JADAVPUR UNIVERSITY
UNDER GUIDANCE OF
PROF. S. DATTA
&
SRI PRASANTA. K. BANERJEE
BY
MALOSHREE MUKHERJEE
2ND YEAR, 4TH SEMESTER,
MASTER OF CHEMICAL ENGINEERING
ROLL NO: 001310302020
YEAR: 2014-2015
DEPARTMENT OF CHEMICAL ENGINEERING
JADAVPUR UNIVERSITY
KOLKATA – 700032
INDIA
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JADAVPUR UNIVERSITY
DEPARTMENT OF CHEMICAL ENGINEERING
We hereby recommended that the thesis prepared under our supervision by
MALOSHREE MUKHERJEE entitled "TREATMENT OF ORGANIC WASTE
WATER USING GRAPHENE AND GRAPHENE OXIDE" be accepted in
partial fulfilment of the requirement for the degree of master of chemical
engineering in Jadavpur University in the year 2015.
Thesis Advisers:
______________________________ ___________________________
Prof. Siddhartha Datta Sri Prasanta K. Banerjee
Project Supervisor Project Supervisor
Department of Chemical Engineering Department Chemical of Engineering
Jadavpur University Jadavpur University
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JADAVPUR UNIVERSITY
DEPARTMENT OF CHEMICAL ENGINEERING
CERTIFICATE OF APPROVAL
The foregoing thesis entitled “Treatment of Organic waste water using
Graphene and Graphene Oxide” is hereby approved as a creditable study
of an engineering subject carried out and presented in a manner
satisfactory to warrant its acceptance as a pre requisite to the degree for
which it has been submitted. It is understood that by this approval the
undersigned do not necessarily endorse or approve any statement made,
opinion expressed or conclusion drawn therein but approve the thesis only
for the purpose for which it is submitted.
Department of chemical engineering
Jadavpur University
_____________________________ ___________________________
Prof. C Guha
Head of the Department
Department of Chemical Engineering
Jadavpur University
Dean,
Faculty of Engineering and
technology
Jadavpur University
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ACKNOWLEDGEMENT
I am highly grateful to the department of Chemical Engineering of
Jadavpur University for providing me an opportunity to work on the project
topic of “Treatment of organic waste water using Graphene-Graphene
oxide”.
I would like to express a deep sense of gratitude to Prof. S Datta and Sri
Prasanta K. Banerjee , and for allowing me to do the project under elegant
supervision and guidance. I would also like to extend my gratitude to Prof.
Papita Das Saha for her valuable advice for this project. Their
encouragement and their support has been something that is beyond my
words.
I would also like to extend a sincere thanks to my class mates who have
help during this period of project work.
Last but not the least; my parents have been most supportive throughout
the session, which has been one of my major strength.
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ABSTRACT
Adsorption is a highly popularised and commercialised method used for removal
of organic and inorganic compound from waste water. Several adsorbent
are being used to treat waste water from various industries, municipal
wastes. Today the technology is much more bent towards adsorption
because it is cost effective and reduces operational cost; some of the
adsorbent are easily available. Another most important point is that since
adsorption is a surface phenomenon the adsorbents can be reused. Nano
particles find application in treatment of waste water in industries.
Graphene and Graphene Oxide are the examples of such nano particle that
are used as adsorbents and are still being experimented and studied in lab
scale so that it can be used in near future. Graphene and Graphene oxide
was prepared by Modified Hummers method from Graphite powder. It was
then used as an adsorbent for removal of Methylene Blue and Phenolic
compounds. pH, temperature, and adsorbent dosage was varied to study
the thermodynamics and kinetics of the process.
Key words: Adsorption, Nano particle, Modified Hummers method, Phenolic
compounds, pH, Methylene Blue, temperature, adsorbent dosage,
thermodynamics, kinetics.
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CONTENTS
1. Introduction
1.1. Severity Of Water Pollution And Why It Is Needed To Be Checked
1.2. Sources of Organic Waste in Water Bodies from Industries and
why is it needed to be checked and Methods Employed For Their
Removal.
1.3. Adsorption- An Effective Process of Treatment of Waste Water.
1.4. Motivation And Aim Of The Present Work
2. Literature Review
3. Materials used.
4. Objectives of work.
5. Synthesis of Graphene and Graphene oxide.
6. Adsorption studies
6.1. Adsorption isotherms
6.2. Kinetics study
6.3. Thermodynamics of the adsorption process
7. Characterization of Graphene and Graphene oxide nano sheet.
8. Methylene Blue Removal from water using the method of
adsorption- a batch study.
8.1. Preparation of standard stock solution Of methylene blue
8.2. Removal of methylene blue from water using Graphene oxide
8.3. Treatment of methylene blue using Graphene
9. Treatment of phenol using Graphene oxide.
10. References
11. Nomenclature
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1. INTRODUCTION
1.1. SEVERITY OF WATER POLLUTION AND WHY IT IS NEEDED TO
BE CHECKED.
Pollution as defined by the Environmental Protection Act of 2001 states
that “the direct or indirect introduction by man into the environment of
substances, organisms, genetic material or energy that cause or are likely
to cause hazard to human health, harm to living resources or to
ecosystems, or damage to amenities, or interfere with other legitimate uses
of the environment”.
Water is mainly polluted by sewage discharge, run off from agricultural
fields, discharges from industries, aquaculture, shipping, including
bunkering and harbour dredging. As a result of water pollution there is an
increased stress to aquatic life, accumulation of particulate waste and
death of many aquatic organisms and harm to the mankind.
Water pollution has been a major issue across the globe. If this continues
one day it will lead depletion of fresh water. Our global water resources
consist of saline water (97.02%) and fresh water (2.8%). The fresh water
constitutes the surface water (E.g. ice in ice caps, as mixture, as utilizable
water bodies) (2.2%) and ground water (0.6%). Global fresh water
withdrawal from river, lakes and aquifers has been exacerbated by growth
of population. The water sources in India are almost half -flowing and the
aquatic life could be in danger if the excessive uses of water are not
stopped. In India the average rainfall is 3000 billion cc (approx.) and
indiscriminate falling of trees is adversely affecting the rainfall and thus on
the climate. Also the ground water is getting contaminated due to human
intervention. It is needed to put a measure on controlling the waste water
generation because:
a. The fresh water available on earth is very small in quantity.
b. Major quantity constitutes the saline water. It is very difficult and
expensive to convert saline water to fresh water.
c. Many organisms thrive on and in water. Hence one should be aware
that pollution of water can also lead to ecological imbalances.
So we should carefully use water and try to re use the water for our
purposes.
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1.2. SOURCES OF ORGANIC WASTE IN WATER BODIES FROM
INDUSTRIES AND METHODS EMPLOYED FOR THEIR REMOVAL.
Various types of disposal practices of waste in water bodies from water
bodies, is one of the major cause of water pollution. Industrial wastes
constitute both organic and inorganic waste.
As in this project removal of phenol and methylene blue is concerned. Let
us discuss the sources of these organic wastes.
Methylene blue is a type of cationic dye has a wide application in industries
like paper colouring, dying of cotton and wool [12]. MB has harmful effects
on human and as well as animals. It causes harmful effects such as
vomiting, increased heart rate, diarrhea, shock, cyanosis, jaundice. Hence
it is required to remove MB from environment. [13]
Industrial methods employed to remove dyes are: conventional processes
(coagulation, flocculation and bio degradation, adsorption on activated
carbon), established recovery processes (membrane separation, ion
exchange, oxidation). [22]
Phenol has its sources from leather industries, oil refining, steel foundry,
textile manufacturing industries, petroleum refining industries. [20].
Phenol is regarded as a primary pollutant. It has adverse effect on aquatic
life as well as on mankind. Its continuous exposure causes damages in the
central nervous systems, mostly effects pancreas, liver, kidneys. [21].
Therefore it is required to check its entry into water bodies.
Various techniques have been employed for the degradation of phenol, for
example solvent extraction, membrane filtration, photo-catalytic
degradation, electro chemical oxidation. Adsorption is mostly used because
it is cost effective and simple in operation. Different types of adsorbents are
being used to study the removal of phenol e.g.: activated carbon, chitosan,
clay etc. The members of the carbon family have proved to be efficient in
the removal of Phenolic compounds.
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1.3. ADSORPTION- AN EFFECTIVE PROCESS OF TREATMENT OF
WASTE WATER.
Adsorption techniques employ solid adsorbents and are widely used in
industries for the treatment of waste water. Mostly used for treating of
those type of waste water that cannot be biologically degraded. [22]
Adsorption is a process that is due to the result of interaction between solid
adsorbent and the adsorbate. The adsorbate should have an affinity
towards the adsorbent. The adsorbed molecules get accumulated on the
surface of the adsorbent as a result of adsorption. Two types of adsorption
follow namely chemisorptions and physisorptions. In chemisorptions the
interaction between the adsorbate molecules and the adsorbent is strong
since the affinity between them is higher. Chemisorptions may result in the
formation of bond between adsorbate molecules and the adsorbent.
Physisorptions results due to weaker affinity of adsorbate molecules and
the adsorbent. There is no formation of bonds in physisorption.
Adsorption is advantageous over other processes because it generates few
bye products and it is efficient and cost effective process. It also requires
less area it has greater flexibility is designing and operation. [23]
Today nano adsorbents are being used for the treatment of waste water and
Graphene and Graphene oxide a member of carbon family has gained
attention from the scientist and a number of researches are undergoing
with this. Nano technology is thus evolving area today to bring about a new
change in the water treatment as well as water supply systems.
1.4. MOTIVATION AND AIM OF THE PRESENT WORK
This project work aims in degrading the organic compounds such as
phenol and dyes by the process of adsorption with the help of Graphene
and Graphene oxide. Phenols form a major component in effluents of
petroleum refining, leather and textile industries and also in steel foundry],
pesticides and pharmaceuticals Phenols and its compounds are considered
as primary pollutants and harms human beings and aquatic life even at
lower concentration. Methylene Blue is used as a dye is also considered to
be a potent pollutant and can cause different diseases. Hence it is required
to remove MB from environment. Graphene and Graphene oxide are the
new member of the carbon family has because of its characteristics it has
proved to be an area of interest for the researchers.
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2. LITERATURE REVIEW:
Graphitic was first synthesized by Brodie in the year 1859. He repeatedly treated
Ceylon graphite with mixture of potassium chlorate and fuming nitric acid.
After his discovery, many other methods were discovered to make
Graphene and Graphene oxide.. This process came to be known as Brodie
synthesis. [6]
Next method to be discovered was Staudenniaier-Hofmann-Hamdi method.
In this method potassium chlorate was added to the mixture of
concentrated Sulphuric acid & conc. Nitric acid and graphite. The
potassium chlorate was then added slowly into the mixture and stirred and
was cooled for one week. Inert gases such as CO2 or N2, chlorine dioxide
was removed. This process consumed more than 10 grams of potassium
chlorate for each gram of synthesised graphite. This process was time
consuming and was toxic and hazardous and was prone to explosion. [6]
Next method was Hummer‟s method in which preparation of Graphene
oxide was very fast and less fatal and less prone to injuries. In this process,
graphite was treated with conc. sulphuric acid and NaNO3 & KMNO4. Ice
bath was used to remove heat from the process. [6]
Synthesis of Graphene- Graphene oxide from modified Hummer‟s method,
the Graphene oxide was prepared in the first step by mixing graphite
powder with conc. H2SO4, next the KMNO4 was added slowly and the
reaction was carried out in an ice bath. The mixture was then kept for
certain time and hydrogen peroxide was added to the mixture to stop
reaction. Then the mixture was sonicated, filtered, and dried at 55ºC for 1
day. Thus the final product Graphene oxide was formed. The dried
Graphene oxide was then mixed with distilled water to wash it thoroughly
and was heated. Then hydrazine hydrate was added and was placed in a
shaker at 120 rpm at 35ºC. Then the mixture was filtered, washed with
water and dried. Thus graphene from graphene oxide was thus made. [11]
High quality reduced graphene oxides (rGO) were prepared from graphite
through oxidation which then followed the solvo thermal reduction method.
The morphology, structure and composition of graphene oxide (GO) and
rGO were characterized under the scanning electron microscope (SEM),
transmission electron microscope (TEM), Raman spectrum, X-ray
diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The
electrochemical performances of rGO that was used as anode material for
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lithium-ion batteries were evaluated in coin-type cells versus metallic
lithium. Results obtained showed that the obtained rGO exhibited an
incremented reversible specific capacity of 561 mAh/g. The rGO had
excellent cycling stability and high-rate capability as anodes of lithium-ion
battery were attributed to its few layers structure, large-surface area of the
nano sheet, and fast transport of Li-ion and electron on the interface of
electrolyte/electrode.[9]
An exceptional physical properties of graphene has also been claimed and
thus the potential for different applications has also increased.[7]
A Batch mode was carried out for aniline to study the effects of different
parameters such as pH, adsorbent dosage, and contact time, temperature
and adsorption capacity. At first the adsorption capacity was calculated
then the effect of pH, adsorbent dosage was seen by plotting a graph. The
adsorption capacity of aniline was found high and stable under neutral and
acidic pH conditions and the adsorption capacity was found to decrease
with higher value of pH. [5]
By varying the adsorbent dosage the adsorption capacity was found to
change. On increasing the adsorbent dosage the removal of aniline
increased, a sharp rise of aniline adsorption was found in between 0.01-
0.05gms of adsorbent. [1]
On varying the contact time with adsorption capacity it was seen that the
adsorption capacity was higher at initial concentration and gently
decreased until equilibrium was attained. This is due to mass transfer
resistances of aniline between solution and solid adsorbent. [2]
Temperature, being an essential parameter in adsorption, was varied and
the effect on adsorption capacity was studied. It was noted that the
adsorption capacity increased from 298 to 328 K, which represented the
endothermic nature of the reaction. The effect was because increase of
temperature had increased the braking of bonds and thus the adsorption
capacity was increased. [2]
The adsorption isotherm was studied. For optimizing the adsorption study
several isotherms were being used in removal of aniline such as, Langmuir,
Freundlich, Temkin and Harkins–Jura. The regression coefficients for each
of the isotherms were calculated. It was seen that the aniline adsorption by
graphene oxide was found to be best fitted in Langmuir isotherm model.
The applicability of four models were found to be Langmuir > Freundlich
>Temkin > Harkins-Jura. [3]
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The adsorption of fluoride from aqueous solution by Graphene was studied
by batch mode. The adsorption capacities and rates of fluoride onto
Graphene at different pH, contact time, and temperature were evaluated.
The experimental results showed that Graphene was an excellent fluoride
adsorbent with maximum adsorption capacity of up to 17.65 mg/g at initial
fluoride concentration of 25 mg/L and at a temperature of 298 K. The
isotherm analysis that was done indicated that the adsorption data
described by Langmuir isotherm model. The Thermodynamic studies
showed that the adsorption was a spontaneous and endothermic
process.[10]
For finding the adsorption kinetics of batch study several models were
studied. The controlling factors that were found were: mass transfer,
diffusion, chemical reaction. The kinetic models that were used: Pseudo-
first-order kinetic model, pseudo second order kinetic model .In first order
which the uptake at equilibrium by the adsorbent and rate constant for
pseudo first order reaction was determined. In Pseudo second order kinetic
model the equilibrium uptake and rate constant for second order reaction
was determined. For Intra particle diffusion model the intra particle
diffusion rate was found. According to intra particle diffusion model, the
plot of uptake should be linear and if these lines pass through the origin
then the intra particle diffusion is the rate controlling step. It was seen that
aniline adsorption followed pseudo second order kinetic model. [4]
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3. MATERIALS USED
The materials that were used for synthesizing graphene and graphene
oxides are :
1. Graphite fine powder- Loba cheme.
2. Potassium permanganate-Merck.
3. Hydrazine hydrate –Merk.
4. Borosil 1000ml flask.
5. 250ml conicals - Borosil.
6. Ice bucket- tarson
7. Sulphuric acid grade 97% - Merck.
8. Hydrochloric acid- Merck.
9. Millipore filter paper- Merk.
10. Filter paper ashless- Whatman.
11. Distilled water.
12. Glass rod.
13. Fresh wraps- Hindalco.
14. Funnel –Borosil.
Materials and apparatus used for experiments:
1. Methylene Blue stain- Merck.
2. Phenol- Nice.
3. Test tubes –Borosil.
Apparatus:
1. UV spectrophotometer.
2. Shaker cum incubator.
3. Hot air oven.
4. Centrifuge.
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4. OBJECTIVES OF WORK
The primary objective of this work is to study the removal of synthetic
organic waste ( dye : Methylene Blue and Phenol as adsorbate) from water
using Graphene and Graphene oxide as adsorbents. The study comprises
of following parts:
1. Preparation of Graphene and Graphene oxide by modified
Hummer‟s method.
2. To study the characterization of the prepared adsorbent,
Graphene and Graphene oxide by the following : A) Scanning electron microscope. B) Fourier Transform Infrared Spectrometer (FTIR) to determine the
nature of bonding present in the activated carbon.
3. To study the effect of adsorbent dosage on adsorption.
4. To study the adsorption with the change of pH.
5. To study the adsorption with change of temperature.
6. To study the effect of change in concentration of the adsorbate on
adsorption.
7. To determine the adsorption isotherms that would best fit the
equilibrium data:
A) Langmuir isotherm.
B) Freundlich isotherm.
C) Temkin isotherm.
8. To determine the kinetic model that would best describe the adsorption process.
a) Pseudo First order kinetic model. b) Pseudo second order kinetic model.
c) Intra particle diffusion model.
9. To study the thermodynamics of the process. To calculate the values of ΔH, ΔS, ΔG for the process of adsorption.
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5. SYNTHESIS OF GRAPHENE AND GRAPHENE OXIDE.
SYNTHESIS OF GRAPHENE
Graphene oxide was prepared by modified Hummer‟s Method. The
synthesis was performed by exfoliating graphite powder in the presence of
potassium permanganate (KMnO4) and concentrated sulfuric acid (H2SO4).
Graphite powder (10.0 gm ) was taken and placed in a conical flask, now
50 ml of concentrated sulphuric acid was slowly added and cool it in ice
bucket and, 6.0 gm of potassium permanganate (KMnO4 ) was slowly added
over 20 min with continuous stirring in ice bucket and after 10 min the
mixture was put in hot water bath with continuous stirring at a
temperature of 313 K for 150 min, the mixture was put on room
temperature for 5 min and then 100 ml of distilled water was added slowly
and temperature maintained in the ice bucket of 15 min. At last 150 ml of
hydrogen peroxide (H2O2) 35% was added very slowly in the solution to stop
the reaction, the solution colour appear as brown yellow. The product
solution was filtered in 0.22µm pore size filter by repeated washing with
distilled water and 10% (HCl) to remove metal ions. The cake deposited on
the filter paper was Graphene Oxide it was then dried in hot air oven at
333 K for 48 hours.
SYNTHESIS OF GRAPHENE OXIDE
The synthesis of Graphene by reducing Graphene oxide was base on the
procedure by F.T. Theme et al. It involved making a solution of 10.0 gm of
Graphene oxide in 100 ml of distilled water and heating it in oven at a
temperature 318 K.
Then 3µl of hydrazine hydrate (H2O4) was added to the solution then the
colour of solution changed from brown to black, and put it in shaker at 120
rpm, 308 K for 150 min. After this the solution was filtered with
membrane filter having 0.22µm pore size, the cake is Graphene which was
dry at 333 K for 48 hour.
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6. ADSORPTION STUDIES
6.1. ADSORPTION ISOTHERMS:
To determine the mechanism of the adsorption process, three adsorption
models were studied. Namely: Langmuir isotherm model, Freundlich
isotherm model and Temkins isotherm model.
6.1.1. Langmuir isotherm model:
The Langmuir model (Langmuir, 1916) assumes that molecules are
adsorbed on discrete sites on the surfaces; each active site adsorbs only
one molecule. The adsorbing surfaces are energetically uniform and there is
no interaction among the adsorbed molecules. This type of model follows
Henry‟s law and has a finite saturation limit valid for wide range of
concentration. Mathematically it is written as:
(1)
6.1.2. Freundlich model :
The Freundlich isotherm (Freundlich, 1906) is an empirical equation that is
based on an exponential distribution of adsorption sites and distribution
energies. It is helpful in describing the adsorption properties. The drawback
of Freundlich isotherm is that it cannot describe the saturation behaviour
of an adsorbent.[19]
It does not follows Henry‟s law and have no saturation limit, hence not
applicable for a wide range of concentrations.
A heterogeneous surface is described by the Freundlich adsorption
isotherm. The equation that describes the mathematical form of the
Freundlich adsorption isotherm is represented described:
ln qe = ln Kf+ 1/n ln Ce (2)
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6.1.3. Temkins isotherm model:
Temkin and Pyzhev considered the indirect effects of adsorbate/ adsorbate
interactions on adsorption isotherms, which are regarded as Temkins model. The heat of adsorption of all the molecules in a layer would decrease with coverage due to adsorbate/adsorbate interactions.
Temkin‟s equation is represented below:
(3)
It also doesn‟t follows Henry‟s Law and has no saturation limit, therefore
cannot be used for wide range of concentrations.
Parameters and regression coefficients obtained from the plots of Langmuir
(Ce/qe versus Ce), Freundlich (log qe versus log Ce) and Temkin (qe versus ln
Ce) and on the basis of the regression coefficients obtained the applicability
of the isotherms were determined.
If the Langmuir model fitted well, then maximum adsorption capacity (qmax)
and kL is also found and will indicate the monolayer adsorption. The RL
value was calculated by using the formula:
RL =1/ (1+ (kL *100)) (4)
If the value of RL lies between 0 and 1 the adsorption is favourable.
If the Freundlich isotherm had fitted well then the KF value was found. The
value of the constant „n‟ indicates how favourable the process is. The value
of 1/n, obtained from the slope from the plot of log qe versus log Ce ranging
between 0 and 1 is a measure of adsorption intensity or surface
heterogeneity, if the process is a heterogeneous adsorption then the value
of 1/n gets closer to zero. Value for 1/n <1 indicates a normal Langmuir
isotherm while 1/n >1 is indicative of cooperative adsorption.[19]
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6.2. KINETIC STUDY:
Kinetic studies were conducted to determine the rate of adsorption and for
finding the equilibrium time for the process of adsorption. The amount of
solute adsorbed by the adsorbent was obtained by collecting aliquots at
different intervals of time. The formula of solute uptake per gram of
adsorbent is given by the mass balance of the concentration of the
solute.[17]
qt=(Ci-Ce)*V/W (5)
Percentage removal of was obtained by the following formula as given
below:
Percentageof sorption= [Ci-Co/Ci]*100 (6)
ADSORPTION KINETIC MODELS:
The adsorption kinetic models are required to design the industrial scale
separation processes. The data that was contact time and temperature
dependant was used for determining the kinetics of the model. The models
that were used for determining the kinetics of the processes were: pseudo
first order, pseudo second order and intra particle diffusion models [18].
Pseudo first order equation given by Lagergren and Svenska can be
represented in linear form by the equation given below.
ln(qe− qt ) = ln qe − k1t (7)
Pseudo second order model:
(8)
Intra particle diffusion model:
To test and identify the type of diffusion model, Weber and Moris proposed
a theory. It is an empirical model which showed that the q varies with t ½ .
This is provided by the equation given below:
qt = kpt 1/2 + C (9)
The regression coefficients were found from the pseudo first order model
(plot of log (qe −qt) versus t), the pseudo second order model (plot of t/qt versus t) and intra particle diffusion model (plot of qt versus t ½) were compared.
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6.3. THERMODYNAMICS OF THE ADSORPTION PROCESS.
To examine the effect of temperature on the adsorption of methylene blue
on Graphene Oxide surface, the Gibbs free energy change (∆G), entropy change (∆S) and enthalpy change (∆H) were calculated by the help of thermodynamic equations from the values obtained experimentally:
The Gibbs free energy change (∆G) can be determined from the equation:
∆G=-RTlnKef (10)
Where R is the universal gas constant (8.314J/molK), T is absolute
temperature in K and Kef is the equilibrium constant or also known as distribution coefficient. [18]
Kef = (Ci-Ce)/Ce = qe/Ce (11)
The plot of ln Kef versus 1/T was used to determine the endothermic or
exothermic nature of the process by comparing the equation of the plot
with Vant Hoff equation. Vant Hoff equation is given by:
-∆H/RT + ∆s/R =ln kef (12)
The intercept of the curve stated the value of the change in entropy of the
system. If the change in entropy is greater than zero the increment of
degrees of freedom at solid liquid interface at the adsorption process. [1]
In addition, the negative value of ∆H indicates that dye adsorption using is
exothermic nature of the adsorbent. At high temperature the thickness of
the boundary layer decreases due to the increased tendency of the dye
molecules to escape from the adsorbent surface to the solution, which
results in a decrease in the adsorption capacity as temperature increases.
The negative value of ∆Gº for all temperatures indicates that the adsorption
is a spontaneous process.
The change in free energy change for physi-sorption lies in between -20 and
0 kJ /mol. Chemi-sorption lies in a range of -80 to -400 kJ /mol. [24]
20
7. CHARACTERIZATION OF GRAPHENE AND GRAPHENE OXIDE
NANO SHEET
7.1. FTIR (Fourier Transform of infrared spectroscopy)
FTIR spectrum was done to confirm the successful oxidation of Graphite
powder to Graphene oxide and Graphene. The presence of different
functional groups of oxygen was confirmed in Graphene and Graphene
oxide. The presence of different types of oxygen functionalities in graphene
were confirmed at broad and wide peak at 2280 cm-1 can be attributed to
the O-H stretching vibrations of the C-OH groups and water.
(Venkateswara Rao K., et al.) The band located at 1710-1720cm-1 has been
assigned to stretching vibration of carboxyl groups on the edges of the layer
planes. (C.Hontoria Lucas et.al.)
Thus FTIR confirmed the presence of hydroxyl group in Graphene and
Graphene oxide. Results obtained using this technique have allowed us to
establish some hypotheses about the type of surface oxygen groups present
in the graphite oxides, but they cannot conclusively establish their
chemical structures.
Figure showing FTIR spectra of G and Graphene oxide before adsorption.
4000 3500 3000 2500 2000 1500 1000 500
0
20
40
60
80
100
% T
Wavenumber (cm-1)
Graphene
Graphene oxide
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7.2. SEM (SCANNING ELECTRON MICROSCOPE)
The SEM micrographs of synthesized GO with different scale bars are given
from the figure, it can be observed that Graphene oxide has layered
structure, which affords ultrathin and homogeneous Graphene films. Such
films are folded or continuous at times and it is possible to distinguish the
edges of individual sheets, including kinked and wrinkled areas. Graphene
and Graphene oxide both from layered structure, irregular and folding as
shown in the images below.
Figure shows SEM micro graphs of Graphene
Figure below shows SEM micrographs of Graphene Oxide
22
8. METHYLENE BLUE REMOVAL FROM WATER USING THE METHOD
OFADSORPTION- A BATCH STUDY
8.1. PREPARATION OF STANDARD STOCK SOLUTION OF
METHYLENE BLUE
A standard stock solution of methylene blue having concentration of 500
mg/L was prepared by taking 500 mg of methylene blue in 1L of distilled
water. The dye was mixed thoroughly with the help of a magnetic stirrer.
After that the solution was stored. From the 500 mg/L solution different
concentration of solutions were prepared by dilution and were kept in
different test tubes.
After dilution, the samples in the test tube were taken and absorbance of
each samples were measured by using UV-spectrophotometer. The
wavelength at which the absorbance was measured is 667nm which is
specific for Methylene Blue. Water was used as a reference solution and
with respect to water the absorbance of each sample was measured.
After getting the absorbance of each solution, a standard curve was plotted
between absorbance Vs concentration. The data and the chart were very
essential because this graph would be used to get unknown concentration
values for known absorbance values which we will be obtaining further in
the experiment.
23
Table given below is showing different absorbance values for different
concentrations of methylene blue.
Concentration (mg/L) Absorbance 1 0.191
5 0.9061 10 1.8 25 2.671
50 8.3 100 16.1
150 29.1 200 38.3 250 53
300 68.2 350 73.1
400 81.4 450 85.1 500 100.7
The figure below is showing a plot of absorbance versus concentration.
y = 0.202xR² = 0.991
0
20
40
60
80
100
120
0 100 200 300 400 500 600
Ab
sorb
ance
A
concentration (mg/L)
absorbance
Linear (absorbance)
24
8.2. REMOVAL OF METHYLENE BLUE FROM WATER USING
GRAPHENE BY ADSORPTION
8.2.1. EFFECT OF OPERATING PARAMETERS ON THE ADSORPTION
OF METHYLENE BLUE:
The operating parameters such as effect of Temperature, pH, adsorbent
dosage and concentration of the adsorbate at different time intervals were
observed.
8.2.2. EFFECT OF VARIATION OF ADSORBENT DOSAGE ON
ADSORPTION:
Method: In four Borosil conical flasks of 250ml, 100 ml of working volume
of methylene blue solution were taken with an initial concentration of
Methylene Blue was 10 mg/L. To the solutions 0.025 gm, 0.050 gm, 0.075
gm and 0.1 gm of Graphene oxide were added respectively. Those solutions
were put into a shaker cum incubator at 150 rpm at 303K. The samples
were collected after different intervals of time i.e. 15 minutes, 30minutes,
45minutes, 60minutes, 120 minutes each and were centrifuged at 10,000
rpm for 12 minutes. The samples were then put under the UV spectro-
photometer and the absorbances were measured. From the absorbances
that were obtained, the concentrations were calculated from the standard
curve that was made before.
Table 1: Table below shows the final concentration obtained for methylene
blue after adsorption by different weights of the adsorbent at different time.
adsorbent
dosage (gm/0.1L of
Methylene Blue)
Initial
concentration
(mg/L)
concentration (mg/L)obtained at different
time intervals
15 min 30 min 45 min 60 min
120 min
0.025 10 6.99 5.39 4.81 3.66 2.02
0.050 10 6.74 5.02 3.85 2.62 0.76
0.075 10 4.56 4.06 2.78 1.74 0.64
0.100 10
2.83 1.42 1.24 0.74 0.59
25
Table 2 : Table below shows the percentage removal after adsorption of
methylene blue on Graphene oxide at different time intervals by variation of
adsorbent dosage.
Figure 1: Figure below shows a plot of percentage removal of methylene
blue versus adsorbent dosage at 120min.
It was observed that the percentage of dye removal increases with the
increase of adsorbent dosage. This was due to the fact that on increasing
the adsorbent dosage, the surface area increased and more number of
adsorption sites was available [14]. It was seen that at 30 minutes the
removal was 85.8 % obtained for 0.100gm/0.1L of methylene blue. So the
optimum adsorbent dosage was taken as 0.100gm/0.1L of methylene blue
for successive experiments.
70
75
80
85
90
95
100
0 0.02 0.04 0.06 0.08 0.1 0.12
% r
em
ova
l of
me
thyl
en
e b
lue
adsorbent dosage((gm/0.1L of methylene blue)
adsorbent
dosage (gm/0.1L of
Methylene Blue )
Initial concentration
(mg/L)
percentage removal of methylene blue
obtained at different intervals
15 min 30 min
45 min
60 min 120 min
0.025 10 30.1 46.1 51.9 63.4 79.8 0.050 10 32.6 49.8 61.5 73.8 92.4 0.075 10 54.4 59.4 72.2 82.6 93.6 0.100 10 71.7 85.8 87.6 92.64 94.1
26
8.2.3. EFFECT OF VARIATION OF INITIAL pH ON ADSORPTION:
Method: The normal pH of methylene blue is 6.8. The initial pH of 10mg/L
of methylene blue was varied by using 0.1N HCl (to make it acidic) and
0.1N NaOH (to make it basic). The different pH of methylene blue was 2,
4,9,11 respectively. Each 0.1 L volume of working solution was transferred
in a 250ml Borosil flask and 0.1 gm of Graphene oxide was put into each
flask. The mixture was put into incubator cum shaker at 303K and
samples were collected at 15 minutes, 30minutes, 45 minutes, 60minutes,
and 120 minutes respectively. The samples were centrifuged at 10,000
rpm for 12 minutes. The samples were then put under the UV spectro-
photometer and the absorbances were measured. From those absorbances
which were obtained, the concentrations were calculated from the standard
curve that was made before. The values obtained from the experiment have
been given below.
Table 3: Table below shows concentration of methylene blue obtained after
adsorption by Graphene oxide at different interval of time and different pH.
Table 4: Table below shows percentage removal of methylene blue obtained
at different initial pH and at different time intervals.
pH of methylene
blue
solution
initial concentration of methylene
Blue (mg/L)
concentration (mg/L) of the adsorbent obtained at different intervals
15 min 30 min
45 min
60 min
120 min
2 10 7.202 7.143 6.108 6.094 3.089
4 10 6.212 4.143 2.123 1.064 1.049
9 10 0.133 0.094 0.074 0.069 0.064
11 10 0.074 0.069 0.049 0.0198 0.0049
pH of
methylene blue
solution
initial
concentration of methylene blue (mg/L)
percentage removal of the adsorbent obtained
after certain intervals
15 min 30
min
45
min
60 min 120
min
2 10 27.98 28.57 38.92 39.066 69.11
4 10 37.8 58.57 78.77 89.36 89.51
9 10 98.67 99.06 99.26 99.31 99.36
11 10 99.26 99.31 99.51 99.8 99.95
27
Figure 2: Figure below shows the percentage removal of methylene blue at
different pH and at 120minutes.
The percentage removal increased with increase in pH of the solution. This
happened because the pH of the solution had changed charge on the
surface of Graphene oxide. At lower pH two equilibriums existed.
The H+ ions compete with the cations of the dye at lower pH. Thus at lower
pH the adsorption was lower. At higher pH values more GO- ions occur
which enhances the electrostatic force of attraction and thus percentage
removal is more. [15]
Figure below shows the adsorption of methylene blue on Graphene oxide.
0
20
40
60
80
100
120
0 2 4 6 8 10 12
% r
em
ova
l of
me
thyl
en
e b
lue
pH
28
8.2.4. EFFECT OF VARIATION OF INITIAL DYE CONCENTRATION
ON ADSORPTION:
Different concentration of the adsorbate i.e. 10mg/L, 20mg/L, 30mg/L, 40
mg/L, 50mg/L of working volume of 0.1 L was taken in 250ml of conical
flasks and 0.100 gm of Graphene oxide was given into it and was put into a
shaker cum incubator at 150 rpm at 303K. The samples were collected
after certain intervals of time i.e. 15 minutes, 30minutes, 45minutes,
60minutes, 120 minutes each and were centrifuged at 10,000 rpm for 12
minutes. The samples were then put under the UV spectro-photometer and
the absorbances were measured. From the absorbances which were
obtained, the concentrations were calculated from the standard curve that
was made before. The values obtained from the experiment have been given
below.
Table 5: Table below shows the effect on different initial concentration of
methylene blue after certain interval of time after adsorption.
concentration of methylene Blue
(mg/L)
concentration (mg/L) of methylene blue obtained after certain intervals after adsorption
15 min
30 min
45 min
60 min
120 min
5 0.039 0.009 0.009 0.005 0.003
20 11.96 10.63 5.19 2.21 0.32
30 22.56 16.43 8.42 4.98 1.05
40 31.67 26.32 24 12.36 3.05
50 39.67 37.5 22.5 12.5 5
Table 6 : Table below shows the effect on percentage removal of methylene
blue versus different concentration of methylene blue after different time
intervals.
concentration of methylene
Blue (mg/L)
percentage removal of methylene blue after adsorption obtained after certain intervals of time
15 min
30 min
45 min
60 min
120 min
5 97.9 98.57 98.92 99.06 99.11
20 40.2 46.85 74.05 88.95 98.4
30 24.8 45.23 72.26 83.43 96.5
40 20.8 34.2 40 69.82 92.37
50 20.66 25 55 75 90
29
Figure: 3 The figure below shows the plot of percentage removal of
methylene blue versus different concentration of methylene blue obtained
after 120 minutes
Percentage removal decreased on increasing the temperature. There are
limited numbers of adsorbent sites present on the Graphene oxide which
becomes saturated after some time. Therefore at larger concentration most
of the molecules are left unadsorbed due to saturation of the binding sites.
[16]
8.2.5. EFFECT OF TEMPERATURE VARIATION ON ADSORPTION:
Into four 250ml conical flask, 0.1L working volume of methylene blue was
taken in each flask and 0.1gm of adsorbent was given in each flask and the
1st flask was placed at 313K, second flask at 308K, third flask at 298K and
the fourth one at 293K and each of the flask was shaken at 150 rpm. The
samples were collected from each flask after certain intervals of time i.e. 15
minutes 30minutes, 45minutes, 60minutes, and 120 minutes each and
were centrifuged at 10,000 rpm for 12 minutes. The samples were then put
under the UV spectro-photometer and the absorbances were measured.
From the absorbances obtained, the concentrations were calculated from
the standard curve that was made before. The values obtained from the
experiment have been given below.
88
90
92
94
96
98
100
0 10 20 30 40 50 60
% r
em
ova
l of
me
thyl
en
e lu
e
initial concentration of methylene blue (mg/L)
30
Table shows below the effect of temperature on adsorption of methylene
blue by Graphene oxide.
Temperature
(K)
initial
concentration of methylene
blue (mg/L)
Concentration obtained after certain intervals
15 min 30 min 45
min
60
min
120
min
313 10 6.63 5.82 5.65 5.09 4.05
308 10 0.98 0.75 0.43 0.32 0.30
298 10 3.21 3.04 2.994 2.32 1.09
293 10 4.32 3.64 2.846 2.624 1.44
Table 7: Percentage removal of methylene blue obtained after temperature
variation at different time intervals:
The figure below shows the plot of percentage removal of methylene blue
versus temperature at 120minutes.
This showed that the reaction is endothermic in nature since with increase
in temperature the percentage removal increases.
0
20
40
60
80
100
120
290 295 300 305 310 315
pe
rce
nta
ge r
em
ova
of
me
thyl
en
Blu
e
T (K)
Temperature (K)
initial concentration of methylene blue
(mg/L)
Percentage removal of methylene blue obtained after different time intervals
15 min
30 min
45 min
60 min
120 min
313 10 33.7 41.76 43.44 49.1 59.5 308 10 90.16 92.43 95.7 96.79 96.99 298 10 67.9 69.6 70.06 76.8 89.1 293 10 56.8 63.6 71.54 73.76 85.54
31
RESULT & DISCUSSION:
Table 8: Table showing adsorption capacity for different concentration of
adsorbate at temperature 303K
weight of adsorbent
(mg) (W)
initial concentration
(mg/L) Ci
volume of solution
(L) V
final concentration
(mg/L)after 2 hours Cf
q e(mg/g)
=(Ci-Cf)*V/W
Ce/qe
(gm/L)
0.1 5 0.1 0.03 4.97 0.006
0.1 30 0.1 1.05 28.95 0.0362
0.1 50 0.1 5 45 0.11
Figure below shows the Langmuir isotherm model:
Results from the graph:
By comparing equation (1) and
Ce/qe = 0.020 Ce + 0.009
(2)
We get,
Slope, m= 0.020, qmax = 1/m =50 mg/g,
Intercept= 0.009, hence kL=1/ (0.009* 303) =0.0634
RL =1/ (1+ (intercept x100)) =0.5263; i.e. 0< RL <1. So the adsorption is
favourable.
ce/qe = 0.020 ce + 0.009R² = 0.991
0
0.02
0.04
0.06
0.08
0.1
0.12
0 1 2 3 4 5 6
Ce
/qe
Ce
Langmuir isotherm
32
FREUNDLICH ISOTHERM:
Table 9: Table below shows adsorption capacity for different adsorbate
concentration at 303K
The figure below shows the freundlich isotherm
From graph slope, m=0.274 and intercept, c=3.340
By comparing equation (3) and
ln qe = 0.274 ln Ce + 3.340
We get, Kf= exp( 3.30)=27.11,
1/n=0.274, n=3.64
ln qe = 0.274ln ce + 3.340R² = 0.978
3.3
3.35
3.4
3.45
3.5
3.55
3.6
3.65
3.7
3.75
3.8
3.85
0 0.5 1 1.5 2
ln q
e
ln ce
Freundlich
weight of adsorbent
(mg) (W)
initial concentration
(mg/L) Ci
vol of sol
(L) V
final concentration
(mg/L)after 2 hours Cf
q e(mg/g) = (CiCf)*V/W
Ce/qe
gm/L
ln Ce ln qe
0.1 30 0.1 1.05 28.95 0.0362 0.048 3.36
0.1 40 0.1 3.052 36.95 0.0826 1.116 3.61
0.1 50 0.1 5 45 0.11 1.61 3.81
33
TEMKIN ISOTHERM MODEL:
Table 10: Table below shows adsorption capacity for different adsorbate
concentration at 303K
The figure below shows Temkin isotherm
Results from the graph:
From graph slope, m=9.837 and intercept, c=27.87
RT/b = B, B= 9.837, T=303K. R=8.314 (J/mol K)
RT ln(A/b)= 27.87
A= 258.936.
qe = 9.837(ln Ce) + 27.87R² = 0.956
0
5
10
15
20
25
30
35
40
45
50
0 0.5 1 1.5 2
qe
ln Ce
Temkin
weight of adsorbent
(mg) (W)
initial concentration
(mg/L) Ci
vol of sol (L)
V
final concentration (mg/L)after 2
hours Ce
q e(mg/g) =
(CiCf)*V/W
ln qe
0.1 30 0.1 1.05 28.95 3.36
0.1 40 0.1 3.052 36.95 3.61
0.1 50 0.1 5 45 3.81
34
Table 11 :Table showing the v alues obtained from Langmuir, Freundlich
and Temkin isotherm model fitting.
Langmuir Freundlich Temkin
kL qmax R² n Kf R2 A b
R²
0.0634 50 0.991 3.64 27.11 0.978 258.936 256.088 0.956
From the results, it can be concluded that for GO adsorbent, the Langmuir isotherm (R2> 0.991) fits the experimental results comparably to that of Freundlich isotherm (R2> 0.978) and Temkin (R2>0.956) indicates a
homogenous surface. The MB ions were occupying only specific sites of the Graphene Oxide adsorbent, which is valid for monolayer adsorption on a surface. [19] The maximum adsorption capacity was found to be 50mg/g.
THERMODYNAMICS:
Table 12: Table below showing the values of ln keq for various1/T
vol
of adsorbate
(L)
Weight of
adsorbent
(mg)
Temper
ature
(K)
value of ln Keq obtained after certain
intervals of time
1/T
(K-1) x10-3 15
min
30
min
45
min
60
min
120
min
0.1 0.1 308 2.215 2.50 3.102 3.406 2.215 3.2
0.1 0.1 298 0.749 0.82 0.850 1.197 0.749 3.33
0.1 0.1 293 0.273 0.55 0.921 1.033 0.273
3.41
0.1
0.1
303 0.929 1.79 1.950 2.532 0.929
3.3
35
The figure below is showing the plot of ln keq versus 1/T
Table 13: Table below is showing the values ∆s and ∆H
Line no.
R2 equation time (hours) ∆s ∆H
1 0.926 ln keq =-15212T-1 + 52.68
1 52.68 -15212
2 0.860 ln keq = -13727T-1
+ 47.40 0.75 47.40 -13727
3. 0.956 ln keq = -12250T-1
+ 42.20 0.50 42.20 -12250
4. 0.865 ln keq= -10788T-1 +
36.95 0.25 36.95 -10788
It is seen from the graph and the table that the ∆s>0. This means that GO
has an affinity towards Methylene blue and ∆s varies between 36.95 J/mol
K to 52.68 KJ/mol K.
The values ∆s>0 indicated about the increment of degrees of freedom at
solid liquid interface at the adsorption process.
In addition, the negative value of ∆H indicates that dye adsorption using
GO is exothermic nature. At high temperature the thickness of the
boundary layer decreases due to the increased tendency of the dye
molecules to escape from the adsorbent surface to the solution, which
4. ln keq= -10788T-1 + 36.95R² = 0.865
3. ln keq = -12250T-1 + 42.20R² = 0.956
2. ln keq = -13727T-1 + 47.40R² = 0.860
1. ln keq = -15212T-1 + 52.68R² = 0.926
0
0.5
1
1.5
2
2.5
3
3.5
4
0.0032 0.00325 0.0033 0.00335 0.0034 0.00345
ln K
eq
T-1 (K-1)
Thermodynamics
1
2
4
3
36
results in a decrease in the adsorption capacity as temperature increases.
The value of ∆H varies in between -15212 J/mol and - 10788 J/mol.
To get the value of ∆G at a given temperature, we will have to consider
formula
∆G= -RTlnKef (7) Considering the values of 60minutes, we get the values of ∆G as follows:
Table14:
Temperatures
(K)
∆G (J/mol) ∆G
(KJ/mol)
303 -6378 -6.37
308 -8721.78 -8.721
298 -2965.65 -2.965
293 -2517.68 -2.517
The negative value of ∆Gº for all temperatures indicates that the adsorption
is a spontaneous process.
The change in free energy change for physi-sorption lies in between -20 and 0 kJ /mol. Chemisorptions lies in a range of -80 to -400 kJ /mol. Hence the values of ∆G lie in between -20KJ/mol and 0 KJ/mol hence the
type of adsorption is physi-sorption.
Table 15: Table below is showing the different values of adorption capacity
and its ratio at different time interval
ci mg/L
vol (L)
mass (gm)
cf
mg/L time hour
qt
mg/g t/q hour/(mg/g)
ln (qe-qt) t1/2
hour1/2
20 0.1 0.1 5.2 0.25 14.8 0.016 1.585 0.5
20 0.1 0.1 4.32 0.5 15.68 0.031 1.38 0.707
20 0.1 0.1 3.19 0.75 16.81 0.044 1.054 0.866
20 0.1 0.1 2.64 1 17.36 0.057 0.841 1
37
Figure below is representing pseudo first order model
Figure below is representing pseudo second order model
y = -1.025x + 1.857R² = 0.990
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 0.2 0.4 0.6 0.8 1 1.2
ln (
qe
-qt)
t(h)
pseudo 1st order
y = 0.047x + 0.007R² = 0.996
0
0.02
0.04
0.06
0.08
0.1
0.12
0 0.5 1 1.5 2 2.5
t/q
t (h)
pseudo second order
38
Figure below is showing intra particle diffusion model
The regression coefficient of pseudo second order was found to be more
than the other model. The regression coefficient is 0.996. Hence the
adsorption follows pseudo second order model.
discussions:
The adsorption follows Langmuir model. That is monolayer
adsorption takes place.
The adsorption follows pseudo second order kinetics.
The adsorption process is endothermic, spontaneous reaction.
y = 5.295x + 12.09R² = 0.988
14.5
15
15.5
16
16.5
17
17.5
18
0 0.2 0.4 0.6 0.8 1 1.2
qt
t1/2
intra particle diffusion
39
8.3. TREATMENT OF METHYLENE BLUE USING GRAPHENE
8.3.1. Variation of adsorbent dosage
Method: In four Borosil conical flasks of 250ml, 100 ml of working volume
of methylene blue solution were taken with an initial concentration of
Methylene Blue was 10 mg/L. To the solutions 0.025 gm, 0.050 gm, 0.075
gm and 0.1 gm of Graphene were added respectively. Those solutions were
put into a shaker cum incubator at 150 rpm at 303K. The samples were
collected after different intervals of time i.e. 15 minutes, 30minutes,
45minutes, 60minutes, 120 minutes each and were centrifuged at 10,000
rpm for 12 minutes. The samples were then put under the UV spectro-
photometer and the absorbances were measured. From the absorbances
that were obtained, the concentrations were calculated from the standard
curve that was made before.
Table 16: Table below shows the final concentration obtained for methylene
blue after adsorption by different weights of the adsorbent at different time.
weight of Graphene
(mg) per 0.1L of methylene blue
initial
concentration (mg/L)
concentration obtained after
differentinterval of time
15
min
30
min
45
min
60
min
120
min
0.025gm 10 7.32 6.826 5.465 4.45 3.4
0.050gm 10 6.72 5.53 4.93 4.06 2.37
0.075 gm 10 3.628 3.425 2.4 2.34 1.22
0.100 gm 10 2.841 2.579 1.336 0.31 0.25
Table 17: Table showing percentage removal at for different adsorbent
Weight of the adsorbent (mg) per 0.1L of adsorbate
percentage removal of methylene obtained after certain time
15 min
30 min
45 min
60 min
120 min
0.025gm 26.8 31.74 45.35 55.5 66
0.050gm 32.8 44.7 50.7 59.4 76.3
0.075 gm 63.72 65.75 76 76.6 87.8
0.100 gm 71.59 74.21 86.64 96.9 97.5
40
Table showing percentage removal of methylene blue, at different interval of
time, for different weights of adsorbent.
It was observed that the percentage of dye removal increases with the increase of adsorbent dosage. This was due to the fact that on increasing
the adsorbent dosage, the surface area increased and more number of adsorption sites was available [14]. It was seen that at 30 minutes the
removal was 74.21 % obtained for 0.100gm/0.1L of methylene blue. So the optimum adsorbent dosage was taken as 0.100gm/0.1L of methylene blue for successive experiments.
8.3.2. EFFECT OF VARIATION OF INITIAL DYE CONCENTRATION
ON ADSORPTION:
Different concentration of the adsorbate i.e. 10mg/L, 20mg/L, 30mg/L, 40
mg/L, 50mg/L of working volume of 0.1 L was taken in 250ml of conical
flasks and 0.100 gm of Graphene was given into it and was put into a
shaker cum incubator at 150 rpm at 303K. The samples were collected
after certain intervals of time i.e. 15 minutes, 30minutes, 45minutes,
60minutes, 120 minutes each and were centrifuged at 10,000 rpm for 12
minutes. The samples were then put under the UV spectro-photometer and
the absorbances were measured. From the absorbances which were
obtained, the concentrations were calculated from the standard curve that
was made before. The values obtained from the experiment have been given
below.
0
20
40
60
80
100
120
0 50 100 150
% r
em
ova
l of
me
thyl
en
e b
lue
time
0.025 gm
0.050 gm
0.075 gm
0.100 gm
41
Table 18: Table below shows the effect on different initial concentration of
methylene blue after certain interval of time after adsorption
Table 19: Table below shows the percentage removal of methylene blue
obtained different intervals of time
Concentration of methylene bluesolution (mg/L)
weight of adsorbent(mg)/0.1Lof adsorbate
concentration of methylene blue(mg/L) obtained at different intervals of time
15 min
30 min
45 min
60 min
120 min
10 0.100gm 2.84 2.57 1.33 0.31 0.25
20 0.100 gm 15.2 10.6
8
5.46 2.63 1.79
30 0.100 gm 26.4 19.6 11.6 9.64 4.86
40 0.100 gm 35.8 21.2 16.5 14.9 13.2
Concentration of methylene blue solution (mg/L)
percentage removal of methylene blue obtained at different intervals of time
15 min 30min 45 min 60 min 120 min
10 71.59 74.21 86.64 96.9 97.5
20 23.8 46.6 72.7 86.85 91.05
30 11.93 34.6 61.3 67.86 83.8
40 10.275 46.9 58.725 62.575 66.825
42
Figure below shows the percentage removal of methylene blue at different
temperature
Percentage removal decreased on increasing the concentration. There are
limited numbers of adsorbent sites present on the Graphene oxide which
becomes saturated after some time. Therefore at larger concentration most
of the molecules are left unadsorbed due to saturation of the binding sites.
[16]
0102030405060708090
100110
0 20 40 60 80 100 120 140
per
cen
tage
rem
ova
l
time (min)
percentage removal Vs time
10 20 30
43
8.3.3. EFFECT OF VARIATION OF INITIAL pH ON ADSORPTION
Method: The normal pH of methylene blue is 6.8. The initial pH of 10mg/L
of methylene blue was varied by using 0.1N HCl (to make it acidic) and
0.1N NaOH (to make it basic). The different pH of methylene blue was 2,
4,9,11 respectively. Each 0.1 L volume of working solution was transferred
in a 250ml Borosil flask and 0.1 gm of Graphene was put into each flask.
The mixture was put into incubator cum shaker at 303K and samples were
collected at 15 minutes, 30minutes, 45 minutes, 60minutes, and 120
minutes respectively. The samples were centrifuged at 10,000 rpm for 12
minutes. The samples were then put under the UV spectro-photometer and
the absorbances were measured. From those absorbances which were
obtained, the concentrations were calculated from the standard curve that
was made before. The values obtained from the experiment have been given
below.
Table 20: Table below shows concentration of methylene blue obtained
after adsorption by Graphene at different interval of time and different pH.
Table 21: Table shows below the percentage removal obtained at different
intervals of time.
pH of the
solution
initial concentration
of the solution (mg/L)
concentration (mg/L) obtained at different interval of time
15 min
30 min
45 min
60 min 120min
pH 3 10 4.69 3.37 2.124 1.65 1.02
pH 5.5 10 3.87 2.76 1.69 0.952 0.31
pH 9.5 10 0.201 0.18 0.092 0.084 0.041
pH 11 10 0.165 0.084 0.054 0.051 0.01
pH of methylene
blue
solution
initial concentration
(mg/L)
percentage removal of the adsorbent obtained at different intervals
15 min 30 min
45 min
60 min 120 min
pH 2 10 27.98 28.57 38.92 39.066 69.11
pH 4 10 37.8 58.57 78.77 89.36 89.51
pH 9 10 98.67 99.06 99.26 99.31 99.36
pH 11 10 99.26 99.31 99.51 99.8 99.95
44
Figure below shows the percentage removal of methylene blue obtained at
different intervals of time
The H+ ions compete with the cations of the dye at lower pH. Thus at lower
pH the adsorption was lower. At higher pH values more GO- ions occur
which enhances the electrostatic force of attraction and thus percentage
removal is more. [15]
0
20
40
60
80
100
120
0 2 4 6 8 10 12
pe
rce
nta
ge r
em
ova
l
pH
percentage removal Vs pH
15 min
45 min
30 min
45
8.3.4. EFFECT OF VARIATION OF TEMPERATURE AT DIFFERENT
TEMPERATURES
Into four 250ml conical flask, 0.1L working volume of methylene blue
was taken in each flask and 0.1gm of adsorbent was given in each flask
and the 1st flask was placed at 313K, second flask at 308K, third flask
at 298K and the fourth one at 293K and each of the flask was shaken at
150 rpm. The samples were collected from each flask after certain
intervals of time i.e. 15 minutes 30minutes, 45minutes, 60minutes, and
120 minutes each and were centrifuged at 10,000 rpm for 12 minutes.
The samples were then put under the UV spectro-photometer and the
absorbances were measured. From the absorbances obtained, the
concentrations were calculated from the standard curve that was made
before. The values obtained from the experiment have been given below.
Table 22 : The table below shows concentration obtained for methylene
blue at different intervals of time
temperature
(K)
initial
concentration (mg/L)
Concentration(mg/L) obtained at
different intervals of time
15min
30min
45min
60min
120min
308 10 0.784 0.499 0.26 0.241 0.22
303 10 2.841 2.579 1.336 0.31 0.25
298 10 3.86 2.97 2.61 1.76 1.09
293 10 4.21 3.56 2.98 2.01 1.56
Table 23: percentage removal of methylene blue obtained at different intervals of time
Temperature
(K)
initial
concentration (mg/L
percentage removal obtained after
certain interval of time
15 min
30 min
45 min
60 min
120 min
308 10 92.16 95.01 97.4 97.59 97.8
303 10 71.59 74.21 86.64 96.9 97.5
298 10 61.4 70.3 73.9 82.4 89.1
293 10 57.9 64.4 70.2 79.9 84.4
46
Figure below shows shows percentage removal obtained at 20° C and 30°C
The percentage removal increases on increase of temperature. This states
that the nature of the reaction is endothermic.
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
per
cen
tage
rem
ova
l
time (min)
percentage removal vs time at different temperature
30 degrees 20
47
8.3.5. RESULTS AND DISCUSSION
ISOTHERM FITTING:
Langmuir isotherm:
Table 24 : The table below shows adsorption capacity obtained at different
concentration:
initial conc
(mg/L)
final conc
(mg/L)
volume of solution (L)
mass (mg)
q (mg/g)
Ce/qe ln ce lnqe
10 0.25 0.1 0.1 9.75 0.025 -1.38 2.27
20 1.79 0.1 0.1 18.21 0.098 0.58 2.90
30 4.86 0.1 0.1 25.14 0.193 1.58 3.22
40 13.27 0.1 0.1 26.73 0.496 2.58 3.2857
Figure below shows Langmuir isotherm model
Equation obtained from the graph:
ce/qe = 0.035ce + 0.023
ce/qe = 0.035ce + 0.023R² = 0.998
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14
ce/q
e
Ce
Langmuir isotherm
48
qmax= 1/0.035 =28.57 mg/g (maximum adsorption capacity)
kL = 1/(28.57 x0.035)= 0.999, (0<KL <1) ( favourable)
Freundlich isotherm:
ln qe = ln Kf+ 1/n ln Ce
Figure below shows Freundlich isotherm
Comparing equation given in the graph
ln qe = 0.191ln ce + 2.834
1/n = 0.191, n=5.235.
Kf = 17.01
R² = 0.865
ln qe = 0.191ln ce + 2.834R² = 0.865
2.85
2.9
2.95
3
3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
0 0.5 1 1.5 2 2.5 3
ln q
e
lnce
Freundlich
49
Temkin isotherm:
qe = (RT/b) ln (ACe)
Figure below shows Temkin isotherm
RT/b=B, RT/b=4.250, T= 303K, =8.314 (J/mol K)
Hence, b=592.73
RTlnA/b= 16.63. A=50.045
R² = 0.883
qe = 4.250 lnce + 16.63R² = 0.883
0
5
10
15
20
25
30
0 0.5 1 1.5 2 2.5 3
qe
ln Ce
Temkin isotherm
50
Thermodynamics of the system:
Table 25: Table below shows the values of ln keq at different temperatures.
Temp
(K)
ln keq
at 15 min
ln keq
at 30 min
ln keq
at 45 min
ln keq
at 60 min
ln keq
at 120
1/T
X10-3 (K-1)
308 2.46 2.49 2.971 3.62 3.70 3.247
303 0.92 0.960 1.211 1.98 3.44 3.3
298 0.46 0.59 0.911 1.14 1.62 3.35
293 0.31 0.4250 0.679 0.98 1.43 3.413
The figure below shows the plot of lnkeq versus 1/T
4. ln keq= -11774 1/T + 40.31R² = 0.797
3. ln keq = -12861 1/T + 44.25R² = 0.779
2. ln keq = -15699 1/T + 54.19R² = 0.864
1. ln keq = -15572 1/T + 54.39R² = 0.877
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0.0032 0.00325 0.0033 0.00335 0.0034 0.00345
ln K
eq
1/T (K-1)
Thermodynamics
1
2
34
51
Let us consider equation 1 from the graph:
ln keq = -15572 1/T + 54.39
And comparing with equation
Where, R is the universal gas constant = (8.314 J/mol K), T in K
-∆H/R= -15572
Or ∆H = 15572 kJ/ mol. (Endothermic reaction)
∆s = 54.39 (∆s >0) (affinity of graphene towards methylene blue).
Values of:
∆ G (308) =-RTlnK = -8.314x308x 2.464287= -6309.59J/ mol
∆ G (303) = -RTlnK = -8.314x303x 0.924214= -2366.64J/ mol ∆ G (298) = -RTlnK = -8.314x398x 0.464158= -1535.88J/ mol
It has been found that ∆G< 0 (spontaneous process).
52
Kinetics of the adsorption process
Table 26: Table below shows different values for determining the kinetic
model.
initial
con (mg/L)
final
con (mg/l)
vol
(L)
wt
(gm)
q
(mg/g)
time
(h)
t/q qe-qt ln (qe-
qt)
t 1/2
20 15.24 0.1 0.1 4.76 0.25 0.052 13.45
2.59 0.5
20 10.68 0.1 0.1 9.32 0.5 0.053 8.89 2.18 0.70
20 5.46 0.1 0.1 14.54 0.75 0.051 3.67 1.30 0.86
20 2.63 0.1 0.1 17.37 1 0.057 0.84 -0.17 1
20 1.79 0.1 0.1 18.21 2 0.109 0 1.4
Pseudo first order kinetic model:
ln(qe − qt ) = ln qe − k1t
Figure below shows pseudo first order model
Comparing with the equation that is obtained from the graph:
ln( qe-qt) = -2.597 t+ 3.326
we get,
ln qe=3.326
k1= -2.597
ln( qe-qt) = -2.597 t+ 3.326R² = 0.958
0
0.5
1
1.5
2
2.5
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
ln (
qe
-qt)
t (h)
pseudo- 1st order
53
Pseudo second order kinetic model:
The equation is given by:
Figure below shows pseudo second order kinetic model
Comparing with equation from the graph:
y = 0.048x + 0.012
1/qe= 0.048
1/k2qe2 =0.012
R2 =0.990.
y = 0.048x + 0.012R² = 0.990
0
0.02
0.04
0.06
0.08
0.1
0.12
0 0.5 1 1.5 2 2.5
t/q
t (h)
pseudo-2nd order
54
Intra particle diffusion model:
qt = kpt 1/2 + C
Figure below shows the intra particle diffusion model.
Comparing with equation we get,
Kp= 5.589
C= thickness of the boundary layer=10.59
R2= 0.690
y = 5.589x + 10.59R² = 0.690
0
2
4
6
8
10
12
14
16
18
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
qt
t 1/2
intra particle diffusion
55
Discussion:
From the isotherm model fitting it can be found that the regression
coefficient of the Langmuir model was 0.998 which is near to unity.
And the regression coefficient was found higher than that of
Freundlich and Temkin‟s. So we conclude that methylene blue
adsorption on Graphene was higher and it followed Langmuir
isotherm model. The maximum mono layer adsorption capacity was
found to be 28.57 mg/gm of Graphene. The dimensionless constant
for Langmuir isotherm RL also stated that the value of RL lies between
0 and 1. So the process is favorable. [Y. Li et al. / Materials Research
Bulletin 47 (2012) 1898–1904].
The thermodynamics of the system was studied and it provided
information about the energy changes involved in the process of
adsorption. The effect of temperature was considered to study the
thermodynamics of the system. The feasibility of the adsorption
process was calculated by the equation:
Where, R is the universal gas constant=8.314J/mol k.
T is the temperature in K.
Kd is called the distribution coefficient.
∆G was found to be negative for each temperature and it was seen
that as the system reached to higher temperature, the negative value
of ∆G was found to be higher, indicating that the adsorption was
more spontaneous when it was conducted at higher temperature. The
positive value of ∆ H showed that the process is endothermic in
nature. [30]. It was also found that ∆s>0. This stated the degree of
randomness increased during adsorption of MB on Graphene.
For determining the kinetics of the adsorption system, we took three
models, basically pseudo first order, pseudo second order and intra
particle diffusion. Among the three models, the regression coefficient
for pseudo second order model is more (i.e.0.990) so it indicated the
adsorption system followed the pseudo second order kinetics.
56
9. TREATMENT OF PHENOL USING GRAPHENE OXIDE
9.1. PREPARATION OF STANDARD STOCK SOLUTION:
A standard stock solution of phenol having concentration of 25 mg/L was
prepared by taking 25 mg of phenol in 1L of distilled water. The phenol was
mixed thoroughly with the help of a stirrer. After that the solution was
stored. From the 25 mg/L solution different concentration of solutions were
prepared by dilution and were kept in different test tubes.
After dilution, the samples in the test tube were taken and absorbance of
each samples were measured by using UV-spectrophotometer. The
wavelength at which the absorbance was measured is 210nm which is
specific for phenol. Water was used as a reference solution and with
respect to water the absorbance of each sample was measured.
After getting the absorbances of each solution, a standard curve was
plotted between absorbance Vs concentration. The data and the chart were
very essential because this graph would be used to get unknown
concentration values for known absorbance values which we will be
obtaining further in the experiment.
Table below shows the absorbances obtained at different concentration
Concentration (mg/L) Absorbances
2 0.1304
5 0.2993
8 0.4596
10 0.6049
15 0.8751
20 1.203
25 1.49
57
Figure below shows the standard curve for phenol
9.2. VARIATION OF THE WEIGHT OF THE ADSORBENT
Different weights of the adsorbent was taken in 0.1 L of 20mg/L of phenol
solution in 250ml of conical flasks and was put into a shaker cum
incubator at 150 rpm at 303K and to it different weights of the adsorbent
was given.. The samples were collected after certain intervals of time i.e. 15
min, 30min, 45min, 60min, 120 min each and were centrifuged at 10,000
rpm for 12 minutes. The samples were then put under the
UVspectrophotometer and the absorbances were checked. From the
absorbances obtained, the concentrations were calculated from the
standard curve that was made before. The values obtained from the
experiment have been given below
y = 0.059xR² = 0.999
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20 25 30
a
b
s
o
r
b
a
n
c
e
concentration
58
Table 27: Table for concentrations obtained at different adsorbent dosage
Table 28 : Percentage removal of phenol at different interval of time is
provided below:
Weight of GO (mg)/0.1L of phenol
final concentration of phenol (mg/L) obtained at different intervals of time
15 min 30 min 45 min 60 min 120 min
0.025 19.633 19.16 18.3 17.93 17.58
0.05 18.68 17.73 17.25 17 16.98
0.075 16.83 15.84 16.63 14.6 12
0.1 14.97 13.27 11.17 9.37 8.86
weight of GO gm/0.1L
of phenol
percentage removal obtained after different intervals of time
15 30 45 60 120
0.025 1.835 4.2 8.5 10.35 12.1
0.05 6.6 11.35 13.75 15 15.1
0.075 15.85 20.77 27 34.6 40
0.1 25.15 33.65 44.15 53.15 55.7
59
Figure below shows the percentage removal obtained at different intervals
of time
It was observed that the percentage of phenol removal increases with the
increase of adsorbent dosage. This was due to the fact that on increasing
the adsorbent dosage, the surface area increased and more number of
adsorption sites was available [14]. It was seen that at 120 minutes the
removal was 55.7 % obtained for 0.100gm/0.1L of methylene blue. So the
optimum adsorbent dosage was taken as 0.100gm/0.1L of methylene blue
for successive experiments.
9.3. VARIATION OF INITIAL pH OF THE ADSORBATE.
Method: The normal pH of phenol is 4.9. The initial pH of 20mg/L of phenol
was varied by using 0.1N HCl (to make it acidic) and 0.1N NaOH (to make it
basic). The different pH of phenol was made 3,6,10 respectively. Each 0.1 L
volume of working solution was transferred in a 250ml Borosil flask and
0.1 gm of Graphene oxide was put into each flask. The mixture was put
into incubator cum shaker at 303K and samples were collected at 15
minutes, 30minutes, 45 minutes, 60minutes, and 120 minutes
respectively. The samples were centrifuged at 10,000 rpm for 12 minutes.
The samples were then put under the UV spectro-photometer and the
absorbances were measured. From those absorbances which were
obtained, the concentrations were calculated from the standard curve that
was made before. The values obtained from the experiment have been given
below.
0
10
20
30
40
50
60
0 50 100 150
pe
rce
nta
ge r
em
ova
l
time
0.025
0.05
0.075
60
Table 29: Table below shows different concentrations obtained at different
pH
Table 30: Table below shows the percentage removal obtained at different
pH.
Table 31: Figure below shows percentage removal obtained at different pH
0
10
20
30
40
50
60
70
0 2 4 6 8 10
pe
rce
nta
ge r
em
ova
l
pH
percentage removal Vs pH
15
30
45
60
120
pH of the solution
concentration(mg/L) of phenol obtained after certain interval time
15 min
30 min
45 min
60 min
120 min
3 16.61 14.81 14.14 12.76 10.87
6 15.6 15.15 13.96 11.22 7.39
10 18.88 18.31 18.05 17.79 16.89
pH of the
solution
percentage removal of phenol obtained after different time
intervals
15
min
30
min
45
min
60
min
120
min
3 16.95 25.95 29.3 36.5 45.68
6 22 30.2 33.6 43.9 63.055
9 5.88 8.42 9.75 11.05 15.3
61
The adsorption of phenol by graphene oxide by the variation of pH was
found decrease on increasing the pH of the solution. This is because the pH
influences on the surface charge of the graphene oxide and on the
dissociation of phenol. At lower pH the adsorption is higher. At higher pH
the phenol forms phenolate anions. These phenolate anions get repelled
from the surface of the graphene oxide due to electrostatic repulsion,
thereby lowering the value of adsorption of phenol. [31]
9.4. VARIATION OF THE CONCENTRATION OF THE ADSORBATE
Different concentration of the adsorbate i.e. 10mg/L, 15mg/L, 20mg/L,
25 mg/L of working volume of 0.1 L was taken in 250ml of conical flasks
and 0.100 gm of Graphene oxide was given into it and was put into a
shaker cum incubator at 150 rpm at 303K. The samples were collected
after certain intervals of time i.e. 15 minutes, 30minutes, 45minutes,
60minutes, 120 minutes each and were centrifuged at 10,000 rpm for 12
minutes. The samples were then put under the UV spectro-photometer
and the absorbances were measured. From the absorbances which were
obtained, the concentrations were calculated from the standard curve that
was made before. The values obtained from the experiment have been
given below.
Table 32: Table below shows different concentration obatained after
different intervals of time
concentration of phenol
(mg/L)
concentration obtained for phenol at different interval of time(mg/L)
15min 30min 45 min 60 min 120 min
10 8.13 6.44 3.69 2.847 2.56
15 13.42 11.89 11.08 8.67 4.74
20 16.10 15.15 13.29 11.22 7.389
25 23.62 23.06 21.93 18.94 16.64
62
Table 33: Table below shows percentage removal obtained at different
interval of time
Figure showing percentage removal versus time at different concentration
Percentage removal decreased on increasing the concentration. There are
limited numbers of adsorbent sites present on the Graphene oxide which
becomes saturated after some time. Therefore at larger concentration most
of the molecules are left unadsorbed due to saturation of the binding sites.
0
10
20
30
40
50
60
70
80
0 50 100 150
% r
em
ova
l of
ph
en
ol
time (min)
10 mg/L
15 mg/L
20 mg/L
25 gm/L
Concentration of phenol
(mg/L)
percentage removal of phenol obtained at different interval of time
15 min 30min 45min 60min 120min
10 18.7 35.6 63.1 71.6 74.441
15 10.53 20.73 26.13 42.2 55.06
20 19.49 24.25 33.6 43.9 63.1
25 5.52 12.27 12.28 26.04 33.42
63
9.5. VARIATION OF TEMPERATURE
Into four 250ml conical flask, 0.1L working volume of phenol was taken
in each flask and 0.1gm of adsorbent was given in each flask and those
flask were placed at 293K, 298K, 303K, 308K and each of the flask was
shaken at 150 rpm. The samples were collected from each flask after
certain intervals of time i.e. 15 minutes 30minutes, 45minutes,
60minutes, and 120 minutes each and were centrifuged at 10,000 rpm
for 12 minutes. The samples were then put under the UV spectro-
photometer and the absorbances were measured. From the absorbances
obtained, the concentrations were calculated from the standard curve
that was made before. The values obtained from the experiment have
been given below.
Table 34: Table below shows the concentrations obtained after different
interval of time
temperature
(K)
concentration (mg/L) of phenol obtain after different interval of
time
15min 30 min 45 min 60 min 120 min
293 18.16 16.61 14.4 12.97 12.06
298 16.5 14.92 12.54 10.52 9.9
303 14.97 13.27 11.17 9.37 8.86
308 19.36 18.08 15.97 14.1 13.54
Table 35: Percentage removal obtained at different interval of time
temperature (K)
percentage removal of phenol obtained after different interval of time
15 min 30min 45min 60min 120 min
293 9.2 16.95 27.98 35.3 39.7
298 17.47 25.4 37.3 47.4 50.5
303 25.15 33.65 44.15 53.15 55.7
308 3.2 9.6 20.15 29.5 32.3
64
Percentage removal obtained after different interval of time
The percentage removal had increased with increase in temperature. This
showed that the process of adsorption is an endothermic process.
0
10
20
30
40
50
60
0 20 40 60 80 100 120 140
pe
rce
nta
ge r
em
ova
l of
ph
en
ol
time
20
25
30
35
65
9.6. RESULTS AND DISCUSSION:
Isotherm fitting:
Table 36: Table showing different values for fitting into different models
obtained from variation of concentration
Langmuir model :
Figure showing lang muir isotherm
initial
concentration
(mg/L)
final
concentration
(mg/L)
volume (mL)
mass of adsorbent
(mg)
qe ce/qe ln qe ln ce
10 2.56 0.1 0.1
8.44 0.18
2.13
2
0.4
4
15 4.74 0.1 0.1
8.26
0.81
5 2.11
1.9
0
20 7.38 0.1 0.1 12.6
1 0.58 2.53
1.9
9
25 16.64 0.1 0.1
8.36 1.99 2.12
2.8
1
y = 0.05x + 0.219R² = 0.998
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6 7 8
ce/q
e
ce
Langmuir
66
From the graph we obtain, qmax= 1/0.05=20mg/gm
KL=0.228
RL= 1/(1+KL*100) =0.042, i,e. 0<RL<1 (favourable)
Freundlich model :
ln qe = ln Kf+ 1/n ln Ce
figure showing Frundlich isotherm
Comparing with equation of the graph:
1/n=0.499 or n=2.00
ln kf =1.51 or Kf =4.52
T (K)= 303K
y = 0.499x + 1.541R² = 0.999
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 2 2.5
lnq
e
ln Ce
Freundlich
67
Temkin model :
qe = (RT/b) ln (ACe)
Figure below shows Temkin isotherm
Chemical kinetics:
Table 37: Table showing the concentration values at different time intervals
time (hour)
ci (mg/L)
ce (mg/L)
volume L
weight (gm)
qt
(mg/g) t/q qe-qt ln (qe-
qt) t1/2
0.25 10 8.13 0.1 0.1 1.87 0.13 5.57 1.717 0.5
0.5 10 6.44 0.1 0.1 3.56 0.14 3.88 1.355 0.70
0.075 10 3.69 0.1 0.1 6.31 0.011 1.13 0.12 0.273
1 10 2.847 0.1 0.1 7.153 0.13 0.287 -1.24 1
2 10 2.56 0.1 0.1 7.44 0.26 0
y = 1.464x + 7.649R² = 0.268
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2 2.5
qe
ln Ce
Temkin
68
Figure below shows pseudo first order model
Figure below shows pseudo second order model
y = -3.190x + 2.660R² = 0.909
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
ln (
qe
-qt)
time
pseudo first order
y = 0.080x + 0.107R² = 0.992
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.5 1 1.5 2 2.5
t/q
t
pseudo second order
69
Figure below shows intra particle diffusion model
It was found that the regression coefficient of pseudo second order
model is greater. Hence it can be concluded that adsorption of phenol
undergoes pseudo second order model.
Discussion:
The adsorption of phenol on graphene is a monolayer adsorption. It
follows Langmuir isotherm.
The adsorption of phenol by graphene oxide by the variation of pH
was found decrease on increasing the pH of the solution. This is
because the pH influences on the surface charge of the graphene
oxide and on the dissociation of phenol. At lower pH the adsorption is
higher. At higher pH the phenol forms phenolate anions. These
phenolate anions get repelled from the surface of the graphene oxide
due to electrostatic repulsion. Thus lowering the adsorption value.
The percentage removal increases on increasing the concentration of
the graphene oxide. This happened because on increasing the dosage
the surface area increases and the number of adsorption sites
increases.
The adsorption follows second order kinetics.
The percentage removal of phenol increases on increasing of
temperature this indicates that the nature of the adsorption id
endothermic.
y = 11.18x - 3.872R² = 0.970
0
1
2
3
4
5
6
7
8
0 0.2 0.4 0.6 0.8 1 1.2
qt
t 1/2
intra particle diffusion
70
10. REFERENCE:
1. Farghali ,A.A. ; Bahgat,M.; Rouby, W.M.A. El; Khedr M.H. ; Journal of
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11. NOMENCLATURE:
Ce equilibrium dye concentration in solution (mg L−1)
Ci initial dye concentration (mg L−1)
Ct dye concentration in the liquid phase at time t
(mg L−1)
∆G◦ Gibbs free energy change (kJ mol−1)
∆H◦ enthalpy of reaction (kJ mol−1)
Kef distribution coefficient for adsorption
KF Freundlich constant (mg g−1) (L g−1)1/n
KL Langmuir constant (L mg−1)
k rate constant
kp sorption rate constant (L mg−1 min−1)
ki intraparticle diffusion rate constant (mg g−1min−0.5)
k1 pseudo-first-order rate constant (min−1)
k2 pseudo-second-order rate constant (g mg−1 min−1)
w weight of adsorbent (g)
n Freundlich adsorption isotherm constant
qt equilibrium dye uptake per g of the adsorbent at time t (mg g−1)
qe equilibrium dye uptake per g of the adsorbents (mg g−1)
qm maximum biosorption capacity (mg g−1)
R universal gas constant (8.314 J mol−1K−1)
R2 correlation coefficient
∆S◦ entropy of reaction (J mol−1 K−1)
T temperature (K)
V volume of the solution (L)