1 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 2 ND YEAR, 4 TH SEMESTER, MASTER OF CHEMICAL ENGINEERING ROLL NO: 001310302020 YEAR: 2014-2015 DEPARTMENT OF CHEMICAL ENGINEERING JADAVPUR UNIVERSITY KOLKATA – 700032 INDIA
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1
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
2
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.
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.
9
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.
10
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
11
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]
12
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]
13
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.
14
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.
15
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.
16
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)
17
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]
18
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.
19
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
21
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
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