Kinetics of the adsorption of Pb(II) ions from aqueous solutions by graphene oxide and thiol functionalized graphene oxide

Journal of Molecular Liquids 209 (2015) 50–57

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Kinetics of the adsorption of Pb(II) ions from aqueous solutions by graphene oxide and thiol functionalized graphene oxide Mohammad Yari a,⁎, Mostafa Rajabi b, Omid Moradi c,⁎, Ali Yari c, M. Asif d, Shilpi Agarwal e, Vinod Kumar Gupta e,f,⁎⁎ a

Department of Chemistry, Eslamshahr Branch, Islamic Azad University, Eslamshahr, Iran Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran Department of Chemistry, Shahre-Qods Branch, Islamic Azad University, Tehran, Iran d Chemical Engineering Department, King Saud University Riyadh, Saudi Arabia e Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India f Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa b c

a r t i c l e

i n f o

Article history: Received 11 March 2015 Received in revised form 9 May 2015 Accepted 12 May 2015 Available online xxxx Keywords: Graphene oxide Cysteamine Thiol functionalization Pb (II) Adsorption Kinetics

a b s t r a c t Adsorption capacity of Pb2+ on graphene oxide and thiol functionalized graphene oxide was well investigated and illustrated in the present work. Variable cysteamine concentrations i.e., 60, 80 and 100 mg were used as functionalizing agent for conversion of graphene oxide to thiol functionalized graphene oxide. The surface of graphene oxide (GO) was functionalized by the use of 60 mg of cysteamine (GO-SH1), by 80 mg of cysteamine (GO-SH2) and by 100 mg of cysteamine (GO-SH3), respectively. The prepared adsorbents were characterized using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The impact of several influential parameters such as adsorption time, pH, temperature and cysteamine concentrations on Pb2+ adsorption was well elucidated and optimized. The optimized values of adsorbent dose, initial concentration of Pb2+, contact time, and pH were found to be 20 mg, 25 mg/L, 60 min and 6 respectively at a temperature of 298 K. The kinetic experimental data for GO surface was well fitted and found to be in good agreement with type (II) of pseudo-second-order model, and for GO-SH1, GO-SH2, and GO-SH3 the experimental data was in good agreement with pseudo first-order model, type (IV) of pseudo-second-order model and type (II) of pseudo-second-order model respectively. Results revealed that the adsorption capacity of Pb2+ on to the developed adsorbent increases with the increase in temperature, hence this process was endothermic in nature. © 2015 Published by Elsevier B.V.

1. Introduction Water pollution nowadays is a global issue due to the rapid urbanization and development of the industrial zone. Among the various noxious contaminants, heavy metals are considered as one of the most toxic ones due to their hazardous effects to aquatic organisms, plants, animals and biotic organisms of the ecosystem. One of the non-biodegradable noxious heavy metal is Pb2 +, which is present in the effluents of many industry and factory outlets such as mining, smelting, galvanization, metal finishing and battery manufacturing [1,2]. Lead is an inorganic toxicant present in natural water environments; studies have

⁎ Corresponding authors. ⁎⁎ Correspondence to: V.K. Gupta, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India. E-mail addresses: [email protected] (M. Yari), [email protected], [email protected] (O. Moradi), [email protected], [email protected] (V.K. Gupta).

http://dx.doi.org/10.1016/j.molliq.2015.05.022 0167-7322/© 2015 Published by Elsevier B.V.

shown that young children, infants and pregnant women are particularly susceptible to unsafe lead levels [3,4]. Many conventional methods have been used for the rapid removal of toxic metal ions from aqueous solutions including sedimentation, chemical treatment, oxidation, electrochemical methodology [5–13], biological treatment, reduction, precipitation, membrane filtration, ion exchange and adsorption [14]. Among all the techniques, adsorption is a well-known equilibrium separation process and an effective method for water decontamination applications [15]. Adsorption was found to be superior over other traditional techniques for water purification and decontamination in terms of initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants. It also does not result in the formation of any other harmful secondary pollutant [15]. So far, researchers have tested many different types of developed adsorbents such as carbon nanotubes [16–23], MWCNTs [24,25], nanoparticles and nanocomposites [26–30], rubber tire [31,32], and other low cost adsorbents [33–38] etc. are used for the removal of noxious impurities from the aqueous solution. Therefore a keen attention and serious effort from researchers are required to remove these noxious metals from the aqueous solution, in order to do this tremendous

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

effort is required to develop an ideal adsorbent which has the ability of rapid removal and fast adsorption of toxic contaminants from environments to a pre-determined safe limit. Since the discovery of single-layer graphene (SLG), it has attracted great interest because of its two dimensionality and unique physical properties such as high intrinsic carrier mobility (∼ 200,000 cm2/ (V s)), quantum electronic transport, tunable band gap, high mechanical strength and elasticity, and superior thermal conductivity [39], high stiffness and strength with Young's modulus of around 1000 GPa and break strength of 130 GPa, and extraordinary electrocatalytic activity and optical properties [40]. Single layer graphene is approximately translucent; it absorbs only 2.3% of the incident light intensity, it is independent of the wavelength in the optical domain. This number is given by π α, where α is the fine structure constant. Thus suspended graphene is colorless. Hence graphene (G) and graphene oxide (GO) derivatives are reported as efficient adsorbents [41], which indicated that graphene oxide was proven to be a promising adsorbent for the adsorption of heavy metals [42]. In the present study, we have synthesized thiol functionalized graphene oxide (GO-G-SH) using the different concentrations of cysteamine: 60, 80 and 100 mg. The impact of influential parameters such as adsorption time, pH, temperature and effect of different concentrations of cysteamine on the kinetic of adsorption Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surfaces was well investigated and studied. 2. Materials and methods 2.1. Materials Materials used in the present work were graphene oxide (GO) (4 mg/mL, Water Dispersion), graphene, N,N-dimethyl formamide (DMF, 99.9%), 1-ethyl-(3-3-dimethylaminopropyl) carbo diimide (EDC, 99%), N-hydroxy succinimide (NHS, 99.9%) and cysteamine hydrochloride ([NH2 (CH2)2SH·HCl], 99.9%) were purchased from Sigma Aldrich. De-ionized water was used throughout the experiments for solution preparation. The aqueous solution of Pb2+ (25 mg/L) was prepared using Pb(NO3)2 (molecular weight, 331.20 g/mol) supplied by Merck, Germany (maximum purity available) and was used as such with any other standardization. To adjust the pH values of the working solution dilute HCl or NaOH solution was used.

further study. All surfaces contain thiol functionalization with different concentrations (GO-SHs) as adsorbent then were purified by filtering in a 0.2 μm membrane, which was later followed by washing with copious amounts of ethanol and water (1:1 (v/v)), and then dried at 80 °C for 24 h. This GO-SHs as adsorbents were used for the removal of Pb2+ from aqueous solution. 2.3. Pb2+ adsorption study The adsorption study of the developed adsorbents was carried out using a batch adsorption experiment, which was performed by adsorbing noxious Pb2+ from the aqueous solution under continuous stirring. The fixed amount of adsorbents i.e., 20 mg each of the surfaces was added into 20 mL of Pb2+ solution with a known initial concentration i.e., 25 mg L−1. The contact time of adsorption of Pb2+ onto GO, GOSH1, GO-SH2 and GO-SH3 surfaces was confirmed by conducting preliminary experiments, from the results obtained, it was found that 60 min, was sufficient to attain equilibrium between GO, GO-SH1, GO-SH2 and GO-SH3 surfaces and the Pb2+ and so this time was used as equilibration time. After each adsorption experiment, the bottles of solutions were placed in an ultrasonic bath and it was operated at predefined temperatures. The Pb2+ and adsorbents samples were filtered through a 0.2 μm cellulose membrane filter and the suspensions containing Pb2 +, GO, GO-SH1, GO-SH2 and GO-SH3 were centrifuged at 4500 rpm for 4 min, and the remaining concentrations of Pb2 + were analyzed using the atomic absorbance spectrophotometry AAS (Perkin-Elmer Analyst 700 (±0.01%)) [43]. The amount of Pb2+ removal by the GO-SHs can be calculated by the difference between the initial and residual concentrations of Pb2+ in the aqueous solution. The removal capacity of Pb2+ on GO-SHs was calculated using Eq. (1) [44]:

qe ¼

  C 0 −Ce V W

2.2. Preparation of GO, GO-SH1, GO-SH2 and GO-SH3 surfaces GO powders (120 mg) was further derivatized to GO-G-SH using cysteamine hydrochloride as functionalizing agent with different concentrations i.e., 60, 80 and 100 mg in ethanol (40 mL) with the aid of a coupling agent, EDC (48 mg) and NHS (30 mg), at 60 °C for 48 h, the whole reaction mixture resulted into products i.e., GO-SH1, GOSH2and GO-SH3 respectively, these are used as adsorbents for the

Fig. 1. SEM image of the surface of GO.

51

Fig. 2. FTIR spectra of GO (A), GO-SH (B).

ð1Þ

52

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

Scheme 1. Scheme of functionalized GO-COOH in order to synthesis G-CO-NH-CH2-CH2-SH (G-SH) surfaces as new adsorbent.

where qe was the amount of Pb2+ taken up by the adsorbent (mg g−1), C0 was the initial Pb2+ concentration (mg L−1), Ce was the Pb2+ concentration (mg L−1) after the adsorption process, W was the adsorbent mass (g) and V was the volume of the Pb2+ solution (L) [45]. Adsorption time curve for the removal of Pb2+ by GO, GO-SH1, GO-SH2 and GO-SH3 as adsorbents was shown in Fig. 3.

3. Result and discussion 3.1. Characterizations of adsorbents The microstructures of surfaces of GO were observed by SEM as adsorbents shown in Fig. 1. It was clearly depicted that the developed adsorbents are porous in nature and microstructures of the surfaces of GO, GO-SH1, GO-SH2 and GO-SH3 adsorbents describe the surface textural and morphological characteristics. The FT-IR spectra of GO were shown in Fig. 2A. All the samples have a strong band at ∼3430 cm−1, which corresponds to characteristic bands of (–OH) [47]. The bond at about ∼1730 cm−1 for GO related of the carboxylic acid group (COO−) [48] and the band at ∼ 1620 cm−1 for GO assigned to (C_C) skeletal stretching. In addition, the band at ∼ 1070 cm− 1 for GO corresponds the (C–O) vibration of various oxygen-containing group. FT-IR spectrum of thiol functionalized graphene oxide using cysteamine as functionalizing agent was shown in Fig. 2B. Evidence of the carboxyl peak at 1705 cm − 1 , hydroxyl peak at near 3405 cm − 1 was observed. When GO was mixed with cysteamine in DMF as solvent and EDC and NHS as chemical initiator reaction, GO-SH was derivatized (Scheme 1). The response between the GO-COOH and cysteamine was confirmed by the appearance of a strong aliphatic C–H stretching vibration at ∼ 2890 cm − 1 , and an amide (I) band at 1620 cm − 1 in the this figures. Presence of a peak at ∼ 1620 cm − 1 strongly suggests the presence of amide group on the surface of GO.

2.4. Kinetic experiments Samples for kinetic adsorption experiments were prepared by adding 20 mg of GO GO-SH1 , GO-SH2 and GO-SH3 as adsorbents into Pb 2 + aqueous solutions (20 mL) of fixed concentration of 25 mg L − 1. After a certain period of time i.e., 10,20, 30, 40, 50, 60, 70 and 80 min the samples were collected and the concentration of Pb 2 + in the aqueous solutions was determined using the atomic absorbance spectrophotometry AAS (Perkin-Elmer Analyst 700 (± 0.01%)). The Pb2+ adsorption capacity at time t (qt), in mg/g, was then calculated using Eq. (2) [46]. qt ¼

  C 0 −Ct V W

ð2Þ

where C0 (mg L−1) was the initial Pb2+ concentration and Ct (mg L−1) was the Pb2+ concentration at time t, V was the volume (L) of Pb2+ solution and W was adsorbent mass (g).

25

qt (mg/g)

20 15 10 5

GO

GSH-6

GSH-8

GSH-10

0 0

10

20

30

40

50

60

70

80

90

t(min) Fig. 3. Effect of contact time on the removal of the Pb2+ using GO, GO-SH1, GO-SH2 and GO-SH3 adsorbents, initial concentration: 25 mg/L; adsorbent dosage: 20 mg and T: 298 K, pH: 6.

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

53

25

A

20

y = 10.942x- 25.427 R² = 0.9769

GO

qt(mg/g)

15

y = 11.59x- 26.70 R² = 0.995 y = 11.585x- 26.301 G-SH2 R² = 0.9604 G-SH1

10 5

G-SH3

0 0

y = 11.888x- 27.05 R² = 0.9555

0.5

1

1.5

2

-5

2.5

3

3.5

4

4.5

ln t

1.6

B

1.4 1.2

GO

log (qe-qt)

1

G-SH1

0.8 y = -0.0246x + 1.5842 y = -0.0233x + 1.5971 R² = 0.894 R² = 0.8894 0.6 G-SH2

0.4

G-SH3

0.2 y = -0.0224x + 1.5761 y = -0.0211x + 1.5458 R² = 0.9308

0 0

R² = 0.9412

10

20

t(min) 30

40

50

60

25

C qt (mg/g)

20 GO y = 4.0152x-12.329

15

R² = 0.9373

y = 4.4242x-13.497 G-SH1

R² = 0.9157 y = 4.5527x-13.019 G-SH2 R² = 0.9501 y = 4.4614x-11.574 G-SH3 R² = 0.9598

10 5 0 0

1

2

3

4

5

6

7

8

t (1/2) Fig. 4. (A) Plot of the Elovich adsorption kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface. (B) Plot of the pseudo first-order adsorption kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface. (C) Plot of the intra-particle diffusion adsorption kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface. Conditions: C0: 25 mg/L of Pb2+; mass of adsorbents: 20 mg; time: 10–80 min; the temperature: 298 K at pH 6.

After the synthesis of the GO-G-SH it was noticed that the frequency vibration at ∼1620 cm−1, ∼ 2890 cm−1, and 3405 cm−1 results in the development of more active sites, which increases its efficiency and leads to the rapid removal of the toxic waste, hence modification of GO with the thiol group leads to the development of active sites and more binding sites for the impurities.

and GO-SH3 surfaces increases with the increase in temperature, hence the process of adsorption of Pb2 + onto developed adsorbent i.e., GO, GO-SH1, GO-SH2 and GO-SH3 adsorbents were found to be endothermic in nature [49].

3.3. Adsorption kinetics study 3.2. Effect of contact time on adsorption Pb(II) ions Impact of contact time is a vital factor in practical applications. Fig. 3 depicts the impact of contact time on the adsorption of Pb2+ on GO, GOSH1, GO-SH2 and GO-SH3 adsorbents. It was observed that the adsorption capacity increased with the increase in time for three temperatures. The equilibrium time was found to be 60 min, at 298 K, 308 K and 318 K, respectively. There was no substantial increase observed in the adsorption capacity of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 adsorbents after 60 min, therefore 60 min was chosen as optimum time or equilibration time at 298 K. The results obtained revealed that the adsorption capacity of Pb2+ onto the developed adsorbent i.e., GO, GO-SH1, GO-SH2

For the adsorbent characteristics one of the most important parameter is the adsorption capacity because it determines how much of the contaminant can be removed from the cleaned solution by a unit mass of the adsorbent. However, high value of adsorption capacities is not sufficient in broad application areas. The kinetics of adsorption process is the second feature that may also strongly constrain the use of the adsorbent. The little kinetics adsorption significantly enlarges the removal time, that causes the adsorption to be inadequate [47]. In the present work, the pseudo-first-order, four types of the pseudo-second-order, the Elovich and the intra-particle diffusion kinetic models were used to test the experimental data.

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M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

Table 1 The pseudo-first-order, the Elovich and the intra-particle diffusion kinetic parameters for adsorption of Pb(II) ions on GO, GO-SH1, GO-SH2 and GO-SH3 surface. Conditions: C0: 25 mg/L of Pb(II) solution; mass of adsorbents: 20 mg; time: 10–80 min; the temperature: 298 K at pH 6. Model

Equation

Pseudo-first-order

log(qe − qt) = log(qe) − k1t

Elovich

qt ¼ β1 ln α β þ β1 ln t

Intra-particle diffusion

qt = ki t0.5 + C

Parameters

q (mg/g) k1 (1/min) R2 X2 α β R2 X2 C Ki (mg/g·min0.5) R2 X2

3.3.1. The Elovich kinetic model The Elovich model equation is generally expressed as [48]:
dqt ¼ α exp −βq2 : dt

ð3Þ

To simplify the Elovich equation, Chien and Clayton assumed that α, β ≫ t and by applying the boundary conditions at and at Eq. (3) becomes qt = 0 at t = 0 Eq. (4) becomes [50]: 1 1 qt ¼ ln α β þ ln t β β

ð4Þ

where α and β are the initial adsorption rate (mg/g min) and desorption constant (g/mg) respectively. The plot of qt against ln t provides a linear relationship which α and β are determined from the slope and intercept of the plot, determined by plotting qt versus ln t (Fig. 4A, Table 1). 3.3.2. The pseudo-first-order kinetic model The pseudo-first-order kinetic model is more suitable for low concentration of solute [51]. The liner form of the pseudo-first-order equation is expressed as follows [49]: logðqe −qt Þ ¼ logðqe Þ−k1 t

Adsorbent

ð5Þ

where qe and qt are the amounts of Pb2+ adsorbed on GO, GO-SH1, GOSH2 and GO-SH3 adsorbents at equilibrium and at time t, respectively, and k1 is the rate constant, determined by plotting ln(qe − qt) versus t (Fig. 4B, Table 1). 3.3.3. The pseudo-second-order kinetic model In 1995, Ho presented a pseudo-second order rate law expression, which demonstrated how the rate depends on the adsorption equilibrium capacity but not the concentration of the adsorbate [52]. The kinetic rate equations can be rewritten as follows:

GO

GO-SH1

GO-SH2

GO-SH3

250 0.004 0.976 6.53 212 0.004 0.889 7.91 25 0.038 0.937 11.16

250 0.004 0.995 4.72 217 0.005 0.894 7.21 27 0.032 0.915 12.07

111 0.003 0.960 6.83 222 0.006 0.930 8.09 27 0.031 0.950 10.91

111 0.003 0.955 6.23 243 0.006 0.941 8.14 25 0.035 0.959 11.71

where qe was the amount of adsorbate at equilibrium (mg g−1); t was the reaction time (min); qt was the amount of adsorbate at time t (mg g−1); and k2 was the equilibrium rate constant of pseudo-second order adsorption (g mg−1 min−1). The pseudo-second order model assumes that one Pb2 + was adsorbed on two adsorption sites on the GO, GO-SH1, GO-SH2 and GOSH3 surfaces [53]: 2þ k2

2A þ Pbsol → A2 PbSolid phase :

ð9Þ

The plots of the four types of the pseudo-second-order model [54] were shown in Fig. 5 A, B, C and D and parameters of the pseudosecond-order kinetic model are presented in Table 2. The initial adsorption rate, h0 is defined as [55]: h0 ¼ k2 q2e

ð10Þ

The results showed that for GO and GO-SH1 surfaces the value of the chi-square statistic (X2) for type (II) of the pseudo-second-order model was low compared with the Elovich, the pseudo-first-order, and the intra-particle diffusion kinetic models because there is only a low difference between the equilibrium capacities observed experimentally (q, exp) with those equilibrium capacities derived from Eq. (8) (q, cal). Moreover, the correlation coefficients (R2 ) for type (II) of the pseudo second-order kinetic model are closest to 1, much higher than the correlation coefficients derived from the Elovich, the pseudo-first-order, and the intra-particle diffusion kinetic models (Table 1); these results (Table 2) suggest that adsorption of Pb2 + on GO and GO-SH1 surfaces followed the type (II) of the pseudo second-order kinetic model. Four types of the pseudo-second-order model were defined as [55]: t 1 1 ¼ þ t qt k21 qe qe

ð11Þ

An integrated pseudo-second order rate law can be obtained from Eq. (6) for the boundary conditions t = 0 to t = t and qt = 0 to qt = t, and was given by [52]:

  1 1 1 1 ¼ þ qt qe k22 q2e t

ð12Þ

1 1 ¼ þ k2 t: ðqe ‐qt Þ qe

  1 qt qt ¼ qe − k23 qe t

ð13Þ

qt ¼ k24 q2e −k24 qe qt t

ð14Þ

dqt ¼ k2 ðqe –qt Þ2 : dt

ð6Þ

ð7Þ

Eq. (7) can be rearranged to obtain a linear form: t t t ¼ þ qt k2 qe 2 qe

ð8Þ

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

55

4.5

A

4 3.5 3 t/qt(min.g/mg)

2.5 2 1.5 y = 0.0049x + 3.7214 y = 0.0048x + 3.5989 y = 0.0099x + 2.4207 y = 0.0094x + 2.3339 R² = 0.9626 R² = 0.9497 R² = 0.9638 R² = 0.9759 1 GO G-SH1 G-SH2 G-SH3 0.5 0 0

10

20

30

40

t(min)

50

60

70

80

90

0.6 GO y = 5.3458x - 0.0516 G-SH1 R² = 0.9987 G-SH2 y = 4.0459x - 0.0169 G-SH3 R² = 0.9514 GO G-SH1 y = 3.4319x - 0.0155 G-SH2 R² = 0.9857 G-SH3 GO y = 2.6475x - 0.0037 G-SH1 R² = 0.9992

0.5

1/qt (g/mg)

0.4 0.3 0.2

B

0.1 0 0

0.02

0.04

0.06 1/t(min-1)

0.08

0.1

0.12

25 GO

qt(mg/g)

20

C

y = 103.68x - 24.808 R² = 0.9402

y = 114.36x - 27.287 G-SH1 R² = 0.9205

15

y = 116.93x - 26.964 G-SH2 R² = 0.943

10

y = 114.48x - 25.205 G-SH3 R² = 0.9508

5 0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

qt/t(mg.min/g) 0.5

D

0.45

qt/t(mg/g.min)

0.4 0.35 0.3 0.25 0.2 0.15 y = 0.0043x + 0.3438 R² = 0.9856

0.1 0.05

y = 0.0044x + 0.325 R² = 0.9766

y = 0.007x + 0.244 R² = 0.999

G-SH1

G-SH2

GO

y = 0.0064x + 0.231 R² = 0.9886

G-SH3

0 0

5

10

15

20

25

qt(mg/g) Fig. 5. (A) type (I) of the pseudo second-order kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface (B) type (II) of the pseudo second-order kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface (C) type (III) of the pseudo second-order kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface (D) type (IV) of the pseudo second-order kinetic of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 surface. Conditions: C0: 25 mg/L of Pb2+; mass of adsorbents: 20 mg; time: 10–80 min; the temperature: 298 K at pH 6.

3.3.4. The intra-particle diffusion kinetic model The Weber–Morris intra-particle diffusion model was used to the experimental data [56], in Eq. (15): qt ¼ ki t0:5 þ C

ð15Þ

where qt was the amount of adsorbate at time t (mg g−1); ki was the intra-particle diffusion rate constant (mg/g min0.5), for intra-particle diffusion model, if the qt versus t0.5 plot go through the origin, the sole rate-limiting step is the intra-particle diffusion [56], determined by plotting qt versus t0.5 (Fig. 4C, Table 1).

56

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57

Table 2 The pseudo second-order kinetic parameters for adsorption of Pb(II) ions on GO, GO-SH1, GO-SH2 and GO-SH3 surface. Conditions: C0: 25 mg/L of Pb(II) solution; mass of adsorbents: 20 mg; time: 10–80 min; the temperature: 298 K at pH 6. Model

Equation

Adsorbent

Pseudo second-order (type I)

t qt

¼ k211q þ q1 t

Pseudo second-order (type II)

t qt

¼

Pseudo second-order (type III)

qt ¼ qe −

Pseudo second-order (type IV)

qt t

e

e

1 qe

þ



1 k22 q2e



1 k23 qe





t t

qt t

¼ k24 q2e −k24 qe qt

qe (mg/g) K21 (g/min·mg) R2 X2 qe (mg/g) K22 (g/min·mg) R2 X2 qe (mg/g) K23 (g/min·mg) R2 X2 qe (mg/g) K24 (g/min·mg) R2 X2

3.4. Comparable studies with other adsorbents The GO and GO-G prepared in this work had a relatively large adsorption capacity of Pb2+ compared to some other adsorbents reported in the literature. Table 3 lists the comparison of contact time of Pb2+ on various adsorbents. The contact time for proposed method in comparison with all of the adsorbents are preferable and superior to the literature which shows satisfactory removal performance for Pb2 + as compared to other reported adsorbents [57–62].

4. Conclusion In summary, the adsorption capacity of Pb2+ on GO, GO-SH1, GOSH2 and GO-SH3 surfaces was studied at 298 K and pH 6, and results obtained showed that there was no substantial increase in the adsorption capacity of Pb2+ on GO, GO-SH1, GO-SH2 and GO-SH3 adsorbents after 60 min, hence 60 min was chosen as optimum and equilibration time. Cysteamine was used as functionalizing agent for functionalizing the GO to GO-G-SH, variable concentrations of cysteamine i.e., 60, 80 and 100 mg were used for the preparation of adsorbents such as GO, GOSH1, GO-SH2 and GO-SH3, respectively. The impact of several influential parameters such as adsorption time, pH, temperature and cysteamine concentrations on Pb2+ adsorption was well elucidated and optimized. The optimized values of adsorbent dose, initial concentration of Pb2+, contact time, and pH was found to be 20 mg, 15 mg/L, 50 min, and 6 respectively, 20 mg, 25 mg/L, 60 min and 6 respectively at temperature 298 K. The kinetic experimental data were tested using different kinetic models such as pseudo-first-order, four types of the pseudo-second-

Table 3 Comparison between various adsorbents for the removal of Pb2+. Adsorbent

Metal

Contact time (min)

References

Retorted shale Hydroxyapatite/polyurethane composite foams Phosphosilicate glass Lemna perpusilla Torr. Phosphorylated sawdust Magnetic hydroxypropyl Chitosan/oxidized multiwalled carbon nanotubes composites GO GO-SHs

Pb Pb

100 600

[57] [58]

Pb Pb Pb Pb

250 210 40 120

[59] [60] [61] [62]

Pb

60 60

Proposed method

GO

GO-SH1

GO-SH2

GO-SH3

250 0.004 0.962 6.17 212 0.004 0.998 2.51 25 0.038 0.940 8.13 92 0.004 0.985 4.85

250 0.004 0.949 6.13 217 0.005 0.951 251 27 0.032 0.920 9.12 90 0.004 0.975 4.98

111 0.003 0.963 6.24 222 0.006 0.985 7.62 27 0.031 0.943 10.10 59 0.007 0.999 4.14

111 0.003 0.975 7.01 243 0.006 0.999 7.30 25 0.035 0.950 9.96 62 0.006 0.988 5.61

order, the Elovich and the intra-particle diffusion kinetic models, the results obtained suggested that adsorption of Pb2 + on GO, GO-SH1, GO-SH2, and GO-SH3 surface was well fitted and found to be in good agreement with type (II) of pseudo-second-order model, pseudo firstorder model, type (IV) of pseudo-second-order model and type (II) of pseudo-second-order model respectively because of higher value of (R2) and low value of (X2). Acknowledgment The authors would like to thank the Islamic Azad, Islamshahr Branch for their financial support. V K G, SA, thank DST for the financial support (Project No. DST/WTI/2K11/352). Support of the Deanship of Scientific Research grant for the Research Group RGP-VPP-292 at King Saud University is appreciated by M. Asif.

References [1] H. Yan, L. Yang, Z. Yang, H. Yang, A. Li, R. Cheng, J. Hazard. Mater. 229–230 (2012) 371–380. [2] L. Fan, C. Luo, M. Sun, X. Li, H. Qiu, Colloids Surf. B: Biointerfaces 103 (2013) 523–529. [3] D. Lin, X. Tian, T. Li, Z. Zhang, X. He, B. Xing, Environ. Pollut. 167 (2012) 138e147. [4] N.A. Kabbashi, M.A. Atieh, A. Al-Mamun, M.E.S. Mirghami, M.Z. Alam, Noorahayu Yahya, J. Environ. Sci. 21 (2009) 539–544. [5] V.K. Gupta, A.K. Jain, G. Maheshwari, Talanta 72 (2007) 1469–1473. [6] V.K. Gupta, M.R. Ganjali, P. Norouzi, H. Khani, A. Nayak, S. Agarwal, Crit. Rev. Anal. Chem. 41 (2011) 282–313. [7] R.N. Goyal, V.K. Gupta, S. Chatterjee, Sens. Actuators B Chem. 149 (2010) 252–258. [8] V.K. Gupta, A.K. Jain, S. Agarwal, G. Maheshwari, Talanta 71 (2007) 1964–1968. [9] R. Jain, V.K. Gupta, N. Jadon, K. Radhapyari, Anal. Biochem. 407 (2010) 79–88. [10] V.K. Gupta, A.K. Singh, S. Mehtab, B. Gupta, Anal. Chim. Acta 566 (2006) 5–10. [11] R.N. Goyal, V.K. Gupta, S. Chatterjee, Electrochim. Acta 53 (2008) 5354–5360. [12] V.K. Gupta, A.K. Singh, M. Al Khayat, B. Gupta, Anal. Chim. Acta 590 (2007) 81–90. [13] V.K. Gupta, R. Prasad, R. Mangla, P. Kumar, Anal. Chim. Acta 420 (2000) 19–27. [14] D. Xu, X. Tan, C. Chen, X. Wang, J. Hazard. Mater. 154 (2008) 407–416. [15] M. Rafatullaha, O. Sulaimana, R. Hashima, A. Ahmad, J. Hazard. Mater. 177 (2010) 70–80. [16] H. Mahmoodian, O. Moradi, B. Shariatzadeha, T.A. Saleh, I. Tyagi, A. Maity, M. Asif, V.K. Gupta, J. Mol. Liq. 202 (2014) 189–198. [17] T.A. Saleh, V.K. Gupta, Environ. Sci. Pollut. Res. 19 (2012) 1224–1228. [18] V.K. Gupta, S. Agarwal, T.A. Saleh, J. Hazard. Mater. 185 (2011) 17–23. [19] V.K. Gupta, A.K. Jain, S.K. Shoora, Electrochim. Acta 93 (2013) 248–253. [20] V.K. Gupta, T.A. Saleh, Environ. Sci. Pollut. Res. 20 (2013) 2828–2843. [21] V.K. Gupta, R. Kumar, Adv. Colloid Interf. Sci. 194 (2013) 24–34. [22] A. Pahlavan, V.K. Gupta, A.L. Sanati, F. Karimi, M. Yoosefian, M. Ghadami, Electrochim. Acta 123 (2014) 456–462. [23] T.A. Saleh, V.K. Gupta, J. Colloids Interface Sci. 371 (2012) 101–106. [24] H. Khani, M.K. Rofouei, P. Arab, V.K. Gupta, Z. Vafaei, J. Hazard. Mater. 183 (2010) 402–409. [25] A. Asfaram, M. Ghaedi, S. Agarwal, I. Tyagi, VK Gupta, RSC Advances 5 (24) (2015) 18438–18450.

M. Yari et al. / Journal of Molecular Liquids 209 (2015) 50–57 [26] V.K. Gupta, R. Jain, A. Mittal, S. Agarwal, S. Sikarwar, Mater. Sci. Eng. C 32 (2012) 12–17. [27] V.K. Gupta, A. Nayak, Chem. Eng. J. 180 (2012) 81–90. [28] V.K. Gupta, R. Jain, S. Agarwal, M. Shrivastava, Mater. Sci. Eng. C 31 (2011) 1062–1067. [29] F. Nekouei, S. Nekouei, I. Tyagi, V.K. Gupta, J. Mol. Liq. 201 (2015) 124–133. [30] M. Ghaedi, S. Hajjati, Z. Mahmudi, I. Tyagi, S. Agarwal, A. Maity, V.K. Gupta, Chem. Eng. J. 268 (2015) 28–37. [31] V.K. Gupta, Suhas, A. Nayak, S. Agarwal, M. Chaudhary, I. Tyagi, J Mol. Liq. 190 (2014) 215–222. [32] V.K. Gupta, A. Nayak, S. Agarwal, I. Tyagi, J. Colloid Surface Sci. 417 (2014) 420–430. [33] V.K. Gupta, A. Mittal, J. Mittal, J. Colloid Interface Sci. 344 (2010) 497–507. [34] V.K. Gupta, S.K. Srivastava, D. Mohan, S. Sharma, Waste Manag. 17 (1998) 517–522. [35] V.K. Gupta, A. Mittal, J. Mittal, J. Colloid Interface Sci. 342 (2010) 518–527. [36] V.K. Gupta, A. Mittal, D. Kaur, A. Malviya, J. Mittal, J. Colloid Interface Sci. 337 (2009) 345–354. [37] V.K. Gupta, I. Ali, T.A. Saleh, A. Nayak, S. Agarwal, RSC Adv. 2 (2012) 6380–6388. [38] A. Mittal, A. Malviya, J. Mittal, V.K. Gupta, J. Colloid Interface Sci. 340 (2009) 16–26. [39] C.Y. Su, Y. Xu, W. Zhang, J. Zhao, X. Tang, C.H. Tsai, L.J. Li, Chem. Mater. 21 (2009) 5674–5680. [40] L. MeiJiao, L. Jing, Y.X. Yu, Z. Chang, Y. Jia, H. Hao, W. XianBao, Mol. Mater. Devices 58 (22) (August 2013) 2698–2710. [41] P. Wang, M. Cao, C. Wang, Y. Ao, J. Hou, J. Qian, Appl. Surf. Sci. 290 (2014) 116–124. [42] Y. Zhang, L. Yan, W. Xu, X. Guo, L. Cui, L. Gao, Q. Wei, B. Du, J. Mol. Liq. 191 (2014) 177–182. [43] G.D. Vukovi, A.D. Marinkovi, S.D. Skapin, M. Risti, R. Aleksi, A.A. Peri-Gruji, P.S. Uskokovi, Chem. Eng. J. 173 (2011) 855–865. [44] O. Moradi, M. Norouzi, A. Fakhri, K. Naddafi, J. Environ. Health Sci. Eng. 12 (2014) 25–27.

57

[45] X. Ren, D. Shao, S. Yang, J. Hu, G. Sheng, X. Tan, X. Wang, Chem. Eng. J. 170 (2011) 170–177. [46] W.M. Algothmi, N.M. Bandaru, Y. Yu, J.G. Shapter, A.V. Ellis, J. Colloid Interface Sci. 397 (2013) 32–38. [47] D.K. Venkata Ramana, Jae Su Yu, K. Seshaiah, Chem. Eng. J. 223 (2013) 806–815. [48] J.C.P. Vaghetti, E.C. Lima, B. Royer, B.M. da Cunha, N.F. Cardoso, J.L. Brasil, S.L.P. Dias, J. Hazard. Mater. 162 (2009) 270–280. [49] Y. Leng, W. Guo, S. Su, C. Yi, L. Xing, Chem. Eng. J. 211–212 (2012) 406–411. [50] Y. Li, Q. Du, T. Liu, X. Peng, J. Wang, J. Sun, Y. Wang, S. Wu, Z. Wang, Y. Xia, L. Xia, Chem. Eng. Res. Des. 91 (2013) 361–368. [51] X. Zhang, C. Cheng, J. Zhao, L. Ma, S. Sun, C. Zhao, Chem. Eng. J. 215–216 (2013) 72–81. [52] Y.S. Ho, Adsorption 10 (2004) 151–158. [53] Hardiljeet K. Boparai, Meera Joseph, Denis M. O'Carroll, J. Hazard. Mater. 15 (2010) 1–8. [54] M.Y. Miah, K. Volchek, W. Kuang, F.H.J. Tezel, Hazard. Mater. 183 (2010) 712–717. [55] J.J. Chen, A.L. Ahmad, B.S. Ooi, J. Environ. Chem. Eng. 3 (2013) 339–348. [56] S. Bayazit, J. Ind. Eng. Chem. 19 (2013) 2064–2071. [57] P.M. Pimentel, G. Gonzalez, M.F.A. Melo, D.M.A. Melo, C.N. Silva Jr., A.L.C. Assuncao, Sep. Purif. Technol. 56 (2007) 348–353. [58] S.H. Jang, B.G. Min, Y.G. Jeong, W.S. Lyoo, S.C. Lee, J. Hazard. Mater. 152 (2008) 1285–1292. [59] C.Y. Kim, H.J. Kim, J.S. Nam, J. Hazard. Mater. 153 (2008) 173–178. [60] Y. Tang, L. Chen, X. Wei, Q. Yao, T. Li, J. Hazard. Mater. 244–245 (2013) 603–612. [61] C. Jeon, J.H. Kim, J. Ind. Eng. Chem. 15 (2009) 910–913. [62] Y. Wang, L. Shi, L. Gao, Q. Wei, L. Cui, L. Hu, L. Yan, B. Du, J. Colloid Interface Sci. 451 (2015) 7–14.