EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES OF CATIONIC RED X-GRL ADSORPTION ON GRAPHENE OXIDE
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Environmental Engineering and Management Journal October 2014, Vol.13, No. 10, 2551-2559
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES
OF CATIONIC RED X-GRL ADSORPTION ON GRAPHENE OXIDE
Jiankun Sun1, Yanhui Li1, Tonghao Liu1, Qiuju Du1, Yanzhi Xia1, Linhua Xia1,
Zonghua Wang1, Kunlin Wang2, Hongwei Zhu2, Dehai Wu2
1
Qingdao University, College of Electromechanical Engineering, Laboratory of Fiber Materials and Modern Textile, the Growing
Base for State Key Laboratory, 308 Ningxia Road, 266071 Qingdao, China
2
Tsinghua University, Key Laboratory for Advanced Manufacturing by Material Processing Technology and Department of
Mechanical Engineering, 100084 Beijing, China
Abstract
Graphene oxide (GO) was prepared from expandable graphite by a modified Hummers’ method and characterized by TEM,
XRD, FTIR, and Raman spectroscopy. The batch adsorption experiments were carried out to study the effect of various
parameters, such as the initial concentration, adsorbent dosage, initial pH, contact time and temperature on adsorption properties
of cationic red X-GRL onto GO. The Langmuir and Freundlich models were used to fit the experimental data of adsorption
isotherms. The kinetic studies showed that the adsorption data followed the pseudo-second order model. Thermodynamic studies
indicated the reaction of cationic red X-GRL adsorbed by GO was a spontaneous and endothermic process. The results indicated
that GO could be considered a promising adsorbent for the removal of dyes from aqueous solutions.
Key words: adsorption, cationic red X-GRL, graphene oxide (GO), kinetics, thermodynamics
Received: September, 2011; Revised final: June, 2012; Accepted: June, 2012
1. Introduction ultrafiltration (Purkait et al., 2003). Adsorption is
growing in popularity due to its advantages of simple
Various types of dyes, more than 100, 000 operation, low cost, rapid treatment and effectiveness
types commercially available, are indispensable to for removing low dye concentration waste streams.
the textile, rubber, plastics, paper and leather Various adsorbents such as clay, perlite, zeolite, and
industries (Robinson et al., 2001). Many of them are unburned carbon (Alpat et al., 2008) have been
toxic and non-biodegradable in nature and stable to developed and used to remove dyes from aqueous
light and oxidation. Effluents containing dyes beyond solution. However, increasingly stringent standard on
permissible concentration can reduce light the quality of drinking water has stimulated a
penetration and photosynthesis (Sun and Yang, 2003) growing effort on the exploiture of new high effcient
and cause irreparable damage to human being as well adsorbents.
as aquatic and terrestrial living beings. Common Recently, graphene is receiving increased
methods for the treatment of dye effluents include attention due its unique structure, unusual physical
adsorption (Harja et al., 2011), electrocoagulation and mechanical properties such as high carrier
(SenthilKumar et al., 2010), oxidation (Malik et al., concentration and mobility (Morozov et al., 2005),
2003), flocculation (Panswed et al., 1986), ozonation high thermal conductivity (Balandin et al., 2008), and
process (Koch et al., 2002), membrane separation high mechanical strength (Lee et al., 2008). Similar
(Ciardelli et al., 2000), and micellar enhanced to graphene, GO also has a layered structure and it
Author to whom all correspondence should be addressed: e-mail: liyanhui@tsinghua.org.cn; xiayzh@qdu.edu.cn; Fax: +86 532 85951842
Sun et al./Environmental Engineering and Management Journal 13 (2014), 10, 2551-2559
can be obtained in high yield by controlled chemical 2.3. Characterization of GO
oxidation of graphite (Park, and Ruoff, 2009). GO
can be easily functionalized with phenolic, carboxyl, The morphology and microstructure of the
epoxide and other groups by oxidation treatment sample were characterized by a Transmission
(Zhang et al., 2010a). electron microscope (TEM, JEM-2100F, operated at
There have been some studies about using GO 200 kV), X-ray diffraction(XRD, Bruker D8
as an adsorbent to remove heavy metals and diffractometer with Cu Kα radiation, λ =1.5418 Å, a
methylene blue from contaminated drinking water scan rate of 0.02°2θ/s from 5 to 70°) , Raman
(Yang et al., 2010, 2011). In addition, some microscope (Renishaw RM2000 Raman microscope)
composites, such as GO /MnO2, GO/Ag (Sreeprasad and Fourier transformation infrared spectra (FTIR,
et al., 2011), GO/ferric hydroxide (Zhang et al., Perkin-Elmer-283B FTIR spectrometer, the wave
2010b), were also developed as adsorbents in water number range from 400 to 4000 cm-1).
purification and showed exceptional adsorption
properties for Hg (II) and arsenate in aqueous 2.4. Batch adsorption experiments
solutions.
However, to our knowledge, few A stock solution of cationic red X-GRL (1000
investigations have been carried on the use of GO as mg L-1) was prepared by dissolving appropriate
an adsorbent for dyes removal. In this work, GO was amounts of cationic red X-GRL in deionized water.
prepared and characterized by TEM, XRD, FTIR, The stock solution was diluted to required
and Raman spectroscopy. The effect of various concentrations before used. The batch adsorption
experimental parameters on cationic red X-GRL experiments were carried out by using the GO as the
adsorption process, such as pH, initial dye adsorbent. 100 mL solution of known X-GRL
concentration, contact time, and temperature were concentration and a certain amount of GO were
studied. Equilibrium isotherm, kinetic and added into 250 mL conical flasks and then shook in a
thermodynamic studies of dye adsorption on GO temperature-controlled water bath shaker (SHZ-
have been studied and analyzed. 82A). The initial pH of GO solution is about 4, so it
is used in the further studies.
2. Material and methods The concentration of cationic red X-GRL was
measured by ultraviolet spectrophotometer (TU-
2.1. Materials 1810, Beijing Purkinje General Instrument Co., Ltd,
China).The absorbance is maxX-GRL=532 nm for
The expandable graphite was purchased from cationic red X-GRL. The adsorption capacity, i.e.
Qingdao Henglide Graphite Co. Ltd., China. amount of cationic red X-GRL adsorbed by GO at
Potassium permanganate, 98% sulfuric acid, sodium equilibrium, was evaluated using the following Eq.
nitrate, hydrochloric acid and 30% hydrogen (1):
peroxide were of analytical grade and purchased
(C 0
Ce (1)
from Sinopharm Chemical Reagent Co. Ltd., China. q )V
e m
The cationic red X-GRL (AR grade) was obtained
from Shanghai Reagents Co. Ltd., China. where qe is the GO adsorption capacity (mg g-1), C0
and Ce are initial and equilibrium concentration of
2.2. Preparation of GO cationic red X-GRL (mg L-1) in solution, m is the
mass of adsorbent (g), V is volume of the solution
GO was synthesized from expandable graphite (L).
by following a modified Hummers' method The dye removal percentage Q (%) at time t is
(Hummers and Offeman, 1958) reported previously calculated by the following Eq. (2):
from our group (Liu et al., 2012 ). In brief, 5.0 g of
Q C0
expandable graphite was dispersed into a mixture of Ct (2)
100%
concentrated sulfuric acid (230 mL), sodium nitrate C 0
(5.0 g) and potassium permanganate (30 g) at 273 K.
After the mixture was stored in refrigerator at 273 K where C0 (mg L-1) is the initial concentration of
for 24 h, it was stirred at 308 K for 30 min and cationic red X-GRL, Ct (mg L-1) is the concentration
diluted with deionized water to 690 mL. Then, the of cationic red X-GRL at time t.
reaction temperature of the suspension was rapidly The effect of pH on cationic red X-GRL
increased to 371 K in an oil bath and maintained for removal was studied by adding 0.03 g GO into 100
30 min. mL of the solution with dye concentration of 50 mg
Finally, 1400 mL distilled water and 100 mL L-1 and adjusting initial pH ranging from 2.0 to 10.5
of 30% H2O2 solution were added after the reaction. at 293 K and agitating for 1.5 h. The pH of the
The mixture was washed with 5% HCl and distilled solution was adjusted with negligible amount of
water several times. After filtration and drying at 283 different concentrations of HNO3 (0.1, 0.05, 0.01 mol
K, GO was obtained. L-1) or NaOH (0.1, 0.05, 0.01 mol L-1) solution.
2552
Equilibrium, kinetic and thermodynamic studies of cationic RED X-GRL adsorption on graphene oxide
The effect of adsorbent dosage on cationic red atoms with dangling bonds in plane terminations of
X-GRL removal was conducted by shaking 100 mL disordered graphite and appears as a strong band
of 100 mg L-1 dye solution containing different GO when the number of GO oxide layers in a sample is
dosage at 293 K. The range of the GO dosage was large (Rao et al., 2009). The G band peak at 1583 cm-
1
from 0.03 to 0.13 g in a step size of 0.02 g. corresponds to an E2g mode of graphite and is
A series of contact time experiments for related to the vibration of sp2-bonded carbon atoms
cationic red X-GRL were carried out at the pH of (Rao et al., 2009; Shen et al., 2009). The second-
solution (pH=4) and temperature of 293 K. 0.6 g GO order 2D band is observed at 2688 cm-1. The strong
was added into 2000 mL solution with different 2D band peak suggests that the synthesized GO has
cationic red X-GRL concentrations of 20 and 40 mg considerable defects (Cuong et al., 2010).
L-1. At the predetermined time, the samples were The diffraction peak at 10.69º in the XRD
collected by using a 0.45 µm membrane filter and pattern of GO (Fig. 1c) corresponds to the d-spacing
analyzed. To evaluate the thermodynamic properties, of 0.83 nm which is similar to the reported values of
0.03 g GO was added into 100 mL solution with GO (Shen et al., 2011; Liu et al., 2011). This value is
initial cationic red X-GRL concentrations ranging bigger than the d-spacing (0.34 nm) of pristine
from 20 to 70 mg L-1. The pH of solution was graphite due to the oxidation and the intercalated
adjusted to 4. These samples were then shaken water molecules between the layers (Liu et al., 2011).
continuously for 1.5 h at 293, 313, 333 K, The only one distinct diffraction peak at 10.69º also
respectively. indicates that synthesized sample is high purity GO.
FTIR spectrum is used to qualitatively
3. Results and discussion examine the nature of surface functionality. As
shown in Fig. 1d, GO shows a broad peak at 3420
3.1. Characterization of GO cm-1, which is related to the OH groups. The peak at
1630 cm-1 is due to the skeletal vibrations of
Fig. 1a shows a typical TEM image of GO unoxidized graphitic domains (Pan et al., 2011). The
prepared by the modified Hummers’ method. It can peaks at 1400 and 1100 cm-1 are assigned to
be seen that most GO are of single to a few layers asymmetric COOH stretching vibration and alkoxy
thick and stacked together. C-O groups situated at the edges of the GO sheets,
The Raman spectrum of GO is very sensitive respectively (Murugan et al., 2009). The result is
to the number of atomic layers and the presence of similar to the previous report about that for GO
disorder or defects on carbonaceous materials and it synthesized with chemical oxidation method, the
has proved to be an essential tool to characterize oxidation of graphite involves a chemical process to
graphite and graphene materials (Calizoa et al., oxidize of carbon atoms at the periphery of the
2009). Raman spectrum of GO (Fig. 1b) shows a D graphite matrix to form oxygen-containing groups
band peak at 1363 cm-1 that corresponds to the including hydroxyl, carboxylic, epoxy or alkoxy
breathing mode of κ-point phonons of A1g symmetry. groups (Chen et al., 2011).
The D band is associated with vibrations of carbon
Fig. 1. Characterization of GO: a) TEM image; b) Raman spectrum; c) XRD pattern; d) FTIR spectrum
2553Sun et al./Environmental Engineering and Management Journal 13 (2014), 10, 2551-2559
3.2. Adsorption With further increasing time, the diminishing
availability of the remaining active sites and the
3.2.1. Effect of initial pH on adsorption capacity decrease in the driving force make it take long time
Adsorption of cationic red X-GRL on the to reach equilibrium (Wu et al., 2008), so the
adsorbent was studied at varying pH values. Fig. 2 adsorption rate become slow.
shows the adsorption capacity and removal
percentage of cationic red X-GRL adsorbed by GO. 3.2.4. Effect of temperature on adsorption efficiency
It shows that the initial pH of solution has negligible The effect of temperature on the adsorption of
effect on the cationic red X-GRL adsorption cationic red X-GRL adsorbed by GO was shown in
capacity, so the removal process of cationic red X- Fig. 5. The equilibrium adsorption capacity of GO
GRL from the aqueous solution by GO can be carried increases from a 160.97 to 227.16 mg g-1 at initial
out at both acidic and basic circumstances. dye concentration of 70 mg L-1 with increasing
temperature from 293 to 333 K, indicating that the
3.2.2. Effect of adsorbent dosage on removal adsorption of cationic red X-GRL adsorbed by GO is
efficiency endothermic reaction.
Fig. 3 shows the effect of adsorbent dosage on Increasing temperature can affect the
removal percentage and amount of dye adsorbed by adsorption processes mainly from two aspects.
GO at equilibrium. The removal percentage of Firstly, it decreases solution viscosity and
cationic red X-GRL is more than 94 % at adsorbent correspondingly increases the diffusion rate of the
dosage is 0.3 g L-1, and it increases up to 99 % by adsorbate within the pores of the adsorbents
increasing the adsorbent dosage up to 1.3 g L-1. (Boudrahem et al., 2009). Secondly, it can increase
While the adsorption capacity of GO presents the number of the adsorption sites through breaking
declining trend as the dosage increases, the of some internal bonds near the edge of active
phenomenon may be attributed to the decrease in surface sites of the adsorbents (Acharya et al., 2009).
active sites and agglomeration of the adsorbents. Thus, rising temperature benefits for the
With the increasing of adsorbent dosage, the enhancement of the adsorption capacity of dye onto
active sites of adsorbents provided are greatly more GO.
than the saturated threshold adsorption point, so only
part of active sites are occupied by cationic red, 3.3. Adsorption isotherms
leading to the decrease of adsorption capacity (Li et
al., 2003). In addition, as the adsorbent dosage In order to investigate how cationic red X-
increase, the diffusion path of dye molecules in GO GRL interact with GO and optimize usage of GO, the
becomes longer, resulting in the decrease of amount Langmuir and the Freundlich isotherms were used to
of cationic red X-GRL adsorbed at equilibrium describe adsorption isotherm data obtained at three
(Unuabonah et al., 2008). temperatures (293, 313 and 333 K). The Langmuir
isotherm is based on the assumption of adsorption on
3.2.3. Effect of contact time on removal efficiency a homogeneous surface, equivalent sorption energies
The effect of contact time on cationic red X- and no interaction between adsorbed species (Li et
GRL adsorbed by GO was studied and shown in Fig. al., 2010). The Langmuir equation is expressed as
4. It shows a rapid increase of adsorption capacity in (Eq. 3):
the first 25 min due to the higher driving force
making dye molecules transfer to the surface of the k L q max C e
adsorbents and the availability of the uncovered qe
1 k L Ce (3)
active sites (Aroua et al., 2008).
350 100
200 100
300
80
180 80
250
60
Q (%)
qe (mg/g)
160 60
qe(mg/g)
200
Q(%)
140 40 40
150
100 (mg/L)
120 20 20
100
100 0 50 0
2 4 6 8 10 0.2 0.4 0.6 0.8 1.0 1.2 1.4
pH Dosage (g/L)
Fig. 2. Effect of pH on cationic red X-GRL adsorbed by GO. Fig. 3. The effect of adsorbent dose on the adsorption of
Initial dye concentration, 50 mg L-1; GO dosage, 0.3g L-1 and cationic red X-GRL on GO. Initial concentration, 100 mg L-1;
temperature, 293K pH 4 and temperature, 293K
2554Equilibrium, kinetic and thermodynamic studies of cationic RED X-GRL adsorption on graphene oxide
250
150
120 200
qe (mg/g)
qe (mg/g)
90
150
60 293k
313k
100 333k
20 mg/L
30 40 mg/L
0 50
0 20 40 60 80 100 0 5 10 15 20
Time (min)
Ce (mg/L)
Fig. 4. Effect of contact time on the adsorption of cationic red Fig. 5. Effect of temperature on the adsorption of cationic red
X-GRL adsorbed by GO. Initial concentration, 40mg L-1 and X-GRL adsorbed by GO. Initial dye concentration, 20-70 mg
60 mg L-1; pH 4; GO dosage, 0.3 g L-1 and temperature, 293K L-1; pH 4 and GO dosage, 0.3 g L-1
The above equation can be rearranged to the that of the Freundlich at three temperatures. It
following linear form (Eq. 4): demonstrates that the adsorption behavior of cationic
red X-GRL adsorbed by GO occurs on the
Ce C 1 homogeneous surface of GO and RL values between 0
e and 1 also indicates that the adsorption of cationic
qe qmax qmax k L
(4) red X-GRL onto GO is favorable. It also shows the
maximum adsorption capacity of cationic red X-GRL
where Ce (mg L-1) is the equilibrium dye
on GO is 263.16 mg g-1 at temperature of 333 K,
concentration, qmax (mg g-1) represents the maximum which is higher than that of graphene (238.10 mg g-1)
adsorption capacity. kL (L g-1) is Langmuir constant (Li et al., 2011). The higher adsorption capacity of
related to the energy of adsorption, representing the
GO may be due to the - stacking interaction
affinity between adsorbent and adsorbate.
between cationic red X-GRL molecules and the
Another parameter RL, a dimensionless
surface of GO (Zhao et al., 2011).
equilibrium parameter (Weber and Chakravorti,
1974), which is defined as follows (Eq. 5): 3.4. Kinetic studies
1 To analyze the adsorption kinetics of cationic
RL red X-GRL onto GO, three kinetic models are
1 k L C0 (5) applied, including pseudo-first-order model, pseudo-
where kL (L g-1)is the Langmuir constant and C0 (mg second-order, and intra-particle diffusion model.
L-1)is the highest initial dye concentration. This value The pseudo-first-order equation is expressed
of RL indicates the type of isotherm to be favorable as follows (Eq. 7):
(0< RL 1), linear (RL = 1), or k
log( qe qt ) log qe 1 t (7)
irreversible (RL = 0) (Ngah et al., 2004). 2.303
Freundlich isotherm is an empirical equation
where k1 is the Lagergren rate constant of adsorption
based on an exponential distribution of adsorption
(1/min).
sites and energies and adsorption process on the non-
The values of qe and k1 (Table 2) were
uniform surface of adsorbents (Li et al., 2010). It is
determined from the plot of log(qe-qt) against t (Fig.
represented as (Eq. 6):
7). The lower determination coefficients R2
1 (Sun et al./Environmental Engineering and Management Journal 13 (2014), 10, 2551-2559
5.6
0.10
b
a
0.08
5.2
0.06
Ce/qe (g/L)
lnqe
4.8
0.04
293 K
0.02 313 K
4.4 293 K
333 K
313 K
0.00 333 K
0 5 10 15 4.0
C e (mg/L) -3 -2 -1 0 1 2 3
lnCe
Fig. 6. The equilibrium isotherm for cationic red X-GRL adsorbed by GO: (a) the Langmuir isotherm, (b) the Freundlich
isotherm. Initial dye concentration, 20-70 mg L-1; pH 4; and GO dosage, 0.3 g L-1
Table 1. Parameters of Langmuir and Freundlich adsorption isotherm models for X-GRL adsorbed by GO
Langmuir Freundlich
T (K)
qmax(mg g-1) kL(L g-1) R2 RL n kF(L g-1) R2
293 166.67 1.13 0.9994 0.0125 4.49 88.69 0.9309
313 243.900 1.64 0.9993 0.0086 2.65 133.98 0.9445
333 263.16 2.38 0.9542 0.0060 2.59 170.41 0.9514
The higher determination coefficients (>0.9803) decreasing concentration gradient makes the dye
suggests that the pseudo-second-order model is more molecules take more time into the micropore of GO,
likely to predict the behavior over the whole leading to a low removal rate. CI and CII are non-
experimental range of adsorption. It also means the zero, revealing that the adsorption process is rather
overall rate of cationic red X-GRL adsorption complex and involves more than one diffusive
process seems to be controlled by the chemical resistance and controlling stage.
process through sharing of electrons or by covalent
forces through exchanging of electrons between 3.5. Thermodynamic studies
adsorbent and adsorbate (Malik et al., 2002).
The intra-particle diffusion model is used to The thermodynamic parameters such as the
predict the rate controlling step (Wang et al., 2010). adsorption standard free energy changes (ΔG0), the
It can be written as (Eq. 9): standard enthalpy change (ΔH0) and the standard
entropy change (ΔS0) are obtained from experiments
q k t
1/ 2 (9) at various temperatures using the following equations
t i
C i
(Yao et al., 2010) (Eqs. 10 -12):
where qt is the amount of cationic red X-GRL
G 0 RT ln kL (10)
adsorbed at time t, ki (mg g-1min) is intra-particle
diffusion constant at stage i, Ci is the intercept at
stage i, and the value of Ci is related to the thickness ln K L S 0 / R H 0 / RT (11)
of the boundary layer. If Ci is not equal to zero, it
reveals that the adsorption involves a complex G 0 H 0 T S 0 (12)
process and the intra-particle diffusion is not the only
controlling step for the adsorption (Gerçel et al.,
where R (8.3145 J mol-1 K-1)is the gas constant, kL (L
2007). Fig. 9 shows multi-linearity characterizations
g-1) is the Langmuir constant and T (K) is the
by plotting qt vs. t1/2. The higher determination
absolute temperature (Yao et al., 2010).
coefficients R2 (>0.9804, Table 2) demonstrate the
The values ΔH0 of and ΔS0 can be calculated
experimental data fit to the intra-particle diffusion
from the slopes and the intercepts of the linear
model well. The first sharp stage is the external
straight by plotting lnK0 against 1/T. According to
adsorption stage or instantaneous stage occupying the
the equation (10), the values of ΔG0 can be
major part of adsorption process, indicating the
calculated. Table 3 shows the values of ΔH0, ΔS0 and
external adsorption process is the main controlling
ΔG0 at different initial dye concentrations and
stage. The higher slope in the first stage indicates the
temperatures. The positive standard enthalpy change
rate of dye removal is higher, attributing to the
(ΔH0) suggests that the interaction of cationic red X-
instantaneous availability of active adsorption sites.
GRL adsorbed by GO is endothermic, and the
The following is a lower slope, because the
positive standard entropy change (ΔS0) reveals the
2556Equilibrium, kinetic and thermodynamic studies of cationic RED X-GRL adsorption on graphene oxide
increased randomness at the solid-solution interface The increase in standard free energy changing with
during the adsorption progress (Nuhoglu et al., the rise in temperature shows an increase in
2009). The negative values of ΔG0 at three feasibility of adsorption at higher temperature, which
temperatures indicates the fact that the adsorption of verifies the correctness of the experimental results in
cationic red X-GRL onto GO is a spontaneous theory.
reaction.
2
20 mg/L 1.2
40 mg/L
1
log(qe-qt)
0.8
0
t/qt
-1 0.4
20 mg/L
40 mg/L
-2
0.0
0 20 40 60 80 0 20 40 60 80 100
Time (min) Time (min)
Fig. 7. Pseudo-first order reaction kinetics of cationic red X- Fig. 8. Pseudo-second order reaction kinetics of cationic red X-
GRL adsorbed by GO. Initial concentration, 20 mg L-1 and 40 GRL adsorbed by GO. Initial concentration, 20 mg L-1 and 40
mg L-1; pH 4; GO dosage, 0.3 g L-1 and temperature, 293K mg L-1; pH 4; GO dosage, 0.3 g L-1 and temperature, 293K
150
120
90
qt (mg/g)
60
20 mg/L
30
40 mg/L
0
0 2 4 6 8 10
1/2
t
Fig. 9. Intra-particle diffusion of cationic red X-GRL adsorbed by GO. Initial concentration, 20 mg L-1 and 40 mg L-1; pH 4;
GO dosage, 0.3 g L-1 and temperature, 293K
Table 2. Kinetic parameters for cationic red X-GRL adsorbed by GO
Models Parameters 20 mg L-1 40 mg L-1
Pseudo-first-order qe (mg g-1) 5.70 5.84
k1 (1/min) 0.07 0.06
R2 0.9374 0.9262
Pseudo-second-order qe (mg g-1) 86.8056 143.4720
K2 (g mg-1min-1)﹡10-4 3.0709 143.4720
R2 0.9803 0.9977
Intra-particle diffusion kI 14.0844 22.9664
CI -15.0354 12.9825
R2 0.9913 0.9850
kII 0.2275 0.3707
CⅡ 64.6898 129.8410
R2 0.9941 0.9804
qe (mg g-1) 5.7018 5.8447
Table 3. Thermodynamic parameters for cationic red X-GRL adsorbed by GO
Temperature(K) ΔG0（kJ mol-1） ΔH0(kJ mol-1) ΔS0(J k-1mol-1)
293 -0.2799 15.085 52.44
313 -1.3287
333 -2.3775
2557Sun et al./Environmental Engineering and Management Journal 13 (2014), 10, 2551-2559
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