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activated carbon composite for adsorption of Pb(II) from wastewater
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JECE 785 1–10 Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx
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High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb(II) from wastewater
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Navid Saeidi* , Mehdi Parvini, Zahra Niavarani
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Faculty of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan 35195-363, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 August 2015 Received in revised form 27 September 2015 Accepted 28 September 2015 Available online xxx
Since lead is a carcinogenic and non-biodegradable substance, its removal from water is of vital importance. Of all different removal pollutants techniques the adsorption is a promising method to remove Pb(II). The choice of adsorbent is a key factor to carry out this process efficiently. As already the adsorption of Pb(II) onto different porous materials have been studied, however the adsorption properties of graphene/activated carbon composite (GAC) to metal ions have not been reported yet. In this work, GAC was synthesized from graphene oxide and glucose. The samples were characterized by Xray diffraction, Raman spectroscopy, SEM image and N2 adsorption–desorption isotherms. The GAC possessed high surface area (2012 m2/g), large pore volume (1.61 cm3/g) and mesopore structure. To study the adsorption behavior of Pb(II) on GAC, effects of solution pH, GAC dosage and stirring speed were examined. Afterwards the adsorption isotherms and kinetics of the GAC for removal of Pb(II) were studied by different models. The GAC was found to follow the pseudo-second order kinetic model better than the pseudo-first order. In addition it was understood that the intraparticle diffusion which studied by the Weber–Morris equation addressed the mechanism of the adsorption properly. Since the adsorption isotherm experimental data was fitted better by Langmuir model than Freundlich, the Pb(II) adsorption on the GAC is mainly homogeneous and monolayer. Finally, the maximum adsorption capacity of Pb(II) was measured up to 217 mg/g, which is higher than many other adsorbents. ã 2015 Published by Elsevier Ltd.
Keywords: Graphene Activated carbon composite Mesoporous Pb(II) Adsorption kinetics and isotherms
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1. Introduction
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Lead(II) is a serious environmental health threat because of its non-biodegradability, toxicity, wide-spread presence and tendency to accumulate in living organisms. It can damage nervous system and cause renal kidney disease, mental retardation, cancer and anemia in humans. Water systems are polluted by lead ions in various ways, including mining, painting and printing processes, plumbing, automobile batteries and petroleum industries [1]. As a priority contaminant, the EPA has set a permissible limit of 0.015 mg/L in drinking water [2]. Various methods have been proposed for the treatment of leadcontaminated water such as chemical precipitation [3], electrochemical reduction [4] and ion exchange [1]. However, confinements of these treatment processes appear by virtue of high operational cost, low treatment efficiency and secondary problems from generation of metal-bearing toxic sludge [5]. Among these methods, adsorption is a promising one as it is more efficient, economical and easier to handle than other
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treatment methods. Many researches for adsorption removal of heavy metals including Pb(II) ions have been reported in the literature [1–3,6–8] however, search for adsorbents with high adsorption capacities is still in great need. It means that the choice of adsorbent when attempting to isolate Pb(II) is of special importance. In the past, apart from activated carbon (AC) which has been a traditional adsorbent for different pollutants, the adsorption of Pb (II) onto zeolites [6], CNT [7], graphene [8], graphene oxide (GO) [9] and different graphene based materials such as functionalized magnetic graphene oxide [10], amino siloxane oligomer-linked graphene oxide [11] and SiO2/graphene composite [12] has been researched extensively; however, the adsorption properties of graphene/activated carbon composite (GAC) for metal ions have not been reported yet. GO has been demonstrated to have a very high adsorption capacity in the removal of Pb(II), Cd(II), and Co(II) from aqueous solutions [9,13,14]. The oxygen containing functional groups on the surfaces of GO played important roles in the metal ions sorption. In
* Corresponding author. Fax: +98 231 3354120. E-mail address: [email protected] (N. Saeidi). http://dx.doi.org/10.1016/j.jece.2015.09.023 2213-3437/ ã 2015 Published by Elsevier Ltd.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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graphene/activated carbon composite, AC is annealed with GO. In the composite, a layer of porous AC is coated on graphene sheets, which not only inhibits agglomeration and increases surface area, but also enhances mesoporosity. In other words, chemically modified graphene is ideal filler for the microporous carbon due to its high mesoporous structure. Comparing to large AC particles, it is worth pointing out that the nanosheet composite will reduce the adsorption pathway significantly [15,16]. In this work, high surface area and mesoporous GAC was synthesized by means of GO and glucose as precursor and through a two-step activation method. Then, the resultant GAC was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherms. Afterwards, the adsorption isotherms and kinetics of Pb (II) onto the GAC were studied.
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2. Materials and methods
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2.1. Chemicals
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All chemicals were analytical reagents with mass fraction purity greater than 0.99 and were used without any further purification. All solutions were prepared using deionized water. The pH of working solutions were adjusted with 10% (wt/wt) NaOH and 10% (vol.:vol.) HNO3.
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2.2. Synthesis and purification of GO
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GO powder used in this work was obtained from chemical exfoliation of natural graphite using NaNO3, H2SO4, and KMnO4 following a modified Hummers method [17,18]. The procedure was as follows: 2 g of graphite and 2 g of NaNO3 were placed in a flask and 92 mL of concentrated H2SO4 was added with constant stirring, followed by the slow addition of 12 g of KMnO4 in an ice-water bath. The solution was stirred for 3 h, and the reaction flask was then transferred to a water bath at 30 C and stirred for another 4 h. Next, 200 mL of water was added and the temperature of the suspension was maintained at 95 C for 30 min. Then, 20 mL of H2O2 (30%) was added, whereupon the solution changed color from brown to yellow. After centrifugation at 7000 rpm for 15 min, the solid phase was washed three times with 0.1 M HCl. The sample was then rinsed with deionized water until the pH of the solution was neutral. The desired products were exfoliated using powerful ultrasonication and then were dried under vacuum for 24 h to obtain dark brown GO powder.
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2.3. Synthesis of GAC
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Firstly, 0.15 g of obtained GO powder was added into 100 mL of deionized water and then dispersed by ultrasonication with power of 300 W for 60 min, resulting in an inhomogeneous yellow–brown dispersion. Afterwards, 10 g glucose was added to the dispersion gradually during 5 h ultrasonic bath (80 W). Then, the solvent was vaporized at 60 C in the oven overnight. The dried powder was heated up to 350 C under N2 flow at the rate of 2 C/min in a tubular furnace and held at the temperature for 2 h. For further activation, the obtained carbonized powder underwent a two-step chemical activation. In first step, the powder and ZnCl2 as activating agent with impregnation ration of 1–2, respectively, were added into 100 mL deionized water and agitated for 7 h at 60 C. In fact, ZnCl2 was used to create porosity in the carbonized powder. Evaporation during this time was avoided using a close-up glass container. Then the supernatant solution was separated by vacuum filtration and the remaining solid was oven-dried at 90 C for 2 h. The impregnated sample was placed on a quartz dish, which was then inserted in a quartz tube. The impregnated sample
was heated up to activation temperature (400 C) under N2 flow at the rate of 10 C/min and held at the activation temperature for 1 h. The resulting solids were boiled at about 90 C with 100 mL of 1 M HCl solution for 30 min to leach out the remaining ZnCl2, then filtered and rinsed by warm distilled water several times to remove the excess agent. They were then dried at 100 C for 12 h. The second step was carried out the same as the first one with some alterations as follows: arranging weight ratio of the resultant powder to KOH up to 1–3, soaking for 1 h at 50 C, activating at 750 C under N2 flow at the rate of 10 C/min and holding at the activation temperature for 1 h. KOH played the role of activating agent in the second step. Actually it was used to boost the surface area of the resultant composite. The obtained composite was denoted as GAC.
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2.4. Synthesis of AC from glucose
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Glucose was dried and then carbonized under N2 flow in a tubular furnace at 350 C for 5 h. For further activation, the resultant black powder was impregnated with KOH (KOH/carbon mass ratio 4:1) for 8 h under continuous agitation. Afterwards, it was heated up to 800 C under N2 flow at the rate of 5 C/min and kept at the temperature for 1 h. Then, the sample was washed by boiled deionized water several times and dried at 100 C overnight. The AC prepared from glucose was named as ACG.
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2.5. Structural characteristics
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The XRD patterns were obtained by using a PW1840 diffractometer employing Cu Ka radiation (l = 1.54056 Å), u –2u geometry and a scintillation detector. Each diffraction pattern was recorded at a step of 0.04 and 0.5 s per step. The measurements were made at ambient condition. Raman spectroscopy plots were obtained by a Handheld Raman Analyzer (FirstguardTM, Rigaku). A morphological characterization of GAC was carried out with a scanning electron microscope (MIRA//TESCAN). The sample was placed on a sample holder with an adhesive carbon foil and then the sample was then laid under a vacuum at room temperature. It was coated with gold before the examination. The nitrogen adsorption and desorption isotherms for the sample was measured at 196 C on a Belsorp 18 (BEL Japan, Ltd.). The sample was heated at 200 C for 3 h and degassed overnight. The specific surface area was determined by the Brunauer– Emmet–Teller (BET) method using am (N2 = 16.2 Å2), where am is the molecular area of nitrogen at 196 C. The BET formula is valid over a range of N2 relative partial pressure p/p0 varying from 0.01 to 0.30 [19]. Accordingly, the BET surface area of the sample was calculated on the mentioned range of relative partial pressure. The mesopore volume and the pore size distribution of GAC were determined based on BJH method. The total pore volume, Vtotal, was obtained using the adsorbed nitrogen at a relative pressure p/p0 of approximately 0.99.
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2.6. Adsorption experiments
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The adsorption isotherms were carried out in fixed volumes of pollutant solution (10 mL) at 30 C and pH 5, for 4 h to reach the adsorption equilibrium, using a temperature-controlled shaker operated at 200 rpm. The solutions were prepared by diluting lead nitrate with deionized water (100 mg/L, 10 mL, pH 5). Then, the adsorption capacities were determined by atomic absorption spectrophotometry using a PerkinElmer 2380 instrument. All experiments were performed in duplicate at least and mean values were presented.
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Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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Fig. 1. XRD diffraction patterns of GO and GAC.
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The Pb(II) uptake at the equilibrium qe (mg/g) and removal efficiency (E%) were calculated as follows: qe ¼
ðC 0 C e ÞV m
ð1Þ
E% ¼
C0 Ce 100 C0
ð2Þ
where C0 and Ce (mg/L) are the initial and equilibrium concentrations of Pb(II), respectively; V (L) is the volume of the solution; and m (g) is the dosage of the adsorbent.
Fig. 2. Raman spectra of GO and GAC.
Fig. 3. N2 adsorption isotherm data of GAC (a) and GO (b) as well as pore size distribution of GAC (c).
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Table 1 Structural characteristics of GO, GAC and ACG. Sample
Surface area (m2/g)
Mean pore diameter (nm)
Vmeso
Vtotal
Vmeso/Vtotal
GO GAC ACG
85 2012 660
17.5 3.3 4.3
0.3 1.01 0.40
0.34 1.61 0.72
0.88 0.63 0.55
2.7. Adsorption isotherms
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2.7.1. The Freundlich and Langmuir isotherms are represented by the following equations: Langmuir isotherm [20]
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qe ¼
Q m bC e ð1 þ bC e Þ
ð3Þ
where Ce (mg/L) and qe (mg/g) are the equilibrium concentrations of Pb(II) in the liquid and solid phases, respectively; Qm and b are Langmuir constants. Qm is the maximum metal uptake (mg/g), whereas b is adsorption equilibrium constant (L/g) and related to the energy of adsorption. Freundlich isotherm [21] qe ¼ kf C 1=n e
Fig. 4. SEM image of GAC.
Fig. 5. Effect of GAC dosage on adsorption of Pb(II).
1 1 þ bC 0
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ð4Þ
in which qe (mg/g) and Ce (mg/L) are the equilibrium concentrations of Pb(II) in the adsorbed and liquid phases, kf and n are the Freundlich constants, indicating the adsorption capacity and adsorption intensity. To determine whether the adsorption is favorable, a dimensionless constant separation factor or equilibrium parameter RL is defined based on the following equation [22]: RL ¼
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ð5Þ
where b (L/mg) is the Langmuir isotherm constant, and C0 (mg/L) is the initial Pb(II) concentration. The RL value indicates whether the type of the isotherm is favorable (0 < RL < 1), unfavorable (RL > 1), linear (RL = 1), or irreversible (RL = 0).
Fig. 6. Effect of pH on the adsorption of Pb(II) by GAC.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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2.8. Adsorption kinetics
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The pseudo-first order model was used to analyze the adsorption kinetics. The non-linear pseudo-first order model is expressed as [23]:
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qt ¼ qe ð1 ek1 t Þ 193
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q2e k2 t ð1 þ qe k2 tÞ
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ð9Þ
where qt (mg/g) and qe (mg/g) are the adsorption capacity at time t (min) and at equilibrium, respectively, while k1 (min1) and k2 (min1) are the pseudo-first-order and pseudo-second-order rate constant, respectively. The intra-particle diffusion model (Weber–Morris equation) is expressed as [24]: qt ¼ kid t1=2 þ C
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ð8Þ
This equation can be linearized in logarithmic form as: t 1 ¼ qt ðk2 q2e Þ
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ð7Þ
The pseudo-second order model was also used to the same purpose. The non-linear form of this model is as follows: qt ¼
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ð6Þ
This equation can be linearized in logarithmic form as: ½ðq qt Þ ¼ k1 t ln e qe
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ð10Þ
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where kid (mg/g min) is the intra-particle diffusion rate constant, and C (mg/g) is the constant proportional to the extent of boundary layer thickness.
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3. Results and discussion
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3.1. Characterization of GAC
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As shown in Fig. 1, The XRD pattern of GO showed a sharp peak at about 12 , corresponding to interlayer spacing of 0.85 nm, and no obvious peak at the position of the (0 0 2) peak of graphite (about 26 ) is observed, indicating that the graphite has been fully expanded and successfully oxidized into graphite oxide. After activation and thermal treatment, the sharp diffraction peak of GO vanished, instead a weak and broad peak at 2u = 26 appeared. It can be contributed to the decreasing of the D-spacing value caused by removing most oxygen-functional groups intercalated into spacing of graphite the interlayer during thermal carbonization and reducing the particle size of composite during chemical activation steps [25]. The Raman spectra of GO and GAC are shown in Fig. 2, displaying both two characteristic D and G bands of chemically modified graphene. The Raman spectrum of GO displays a D-band at approximately 1354 cm1 and G-band at about 1615 cm1. The G-band originates from the in-phase vibration of the graphite lattice, while the D-band mainly comes from the structure defects created by the attachment of oxygen functional groups on the carbon basal plane. The D:G intensity ratio of GO is 0.81, indicating the high oxidation degree and/or relatively small domain size. After activation steps and thermal treatment, this ratio was remarkably increased to 1.25. This could be caused by the creation of defects of the sample [25,26]. The N2 adsorption isotherm data of GAC are shown in Fig. 3a. Adsorption measurements were followed by desorption measurements under the same conditions. This isotherm is a combination of type I and IV based on the IUPAC classification and is typical of
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Fig. 7. Kinetics data of Pb(II) onto GAC (a), kinetic modeling of pseudo-first-order model (b) and pseudo-second-order model (c) of Pb(II) adsorption.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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Table 2 Parameters of the kinetic models for Pb(II) adsorption by GAC. Pseudo-first order model
Parameters
Pseudo-first order model
k1 (min1) 0.005 k1 (min1) 0.007 kid,1 (mg/g min) 14.6 C1 3.71
Pseudo-second order model Intra-particle diffusion model (Weber–Morris)
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mesoporous materials with contributions of microporosity. On the contrary, the isotherm of GO (Fig. 3b) is a type IV which shows very low volume of nitrogen uptake compared with GAC. In these materials, capillary condensation normally takes place, leading to hysteresis loops. Micropore filling occurs at very low relative pleasures. From the N2 adsorption–desorption isotherms it was clear that the adsorbed volume increases with increasing p/p0, indicating the wider pore size distribution. The pore size distribution of GAC illustrates in Fig. 3c . The graph reveals that the sample has a well-defined pore structure presenting high mesoporosity (1–25 nm) with ignorable contributions of macroporosity (>25 nm). Table 1 summarizes the textural properties of GAC, GO and ACG. It can be seen that the surface area of GAC is 2012 m2/g, which is close to the theoretical value of graphene (2630 m2/g) and far more than that of thermally reduced graphene reported in other works. As mentioned above, GAC possesses not only very high surface area but also it has mesopore structure and high pore volume. This feature is very useful in different applications including waste water treatment. Many researchers have tried to improve both surface area and mesoporosity of porous materials, in particular activated carbon, simultaneously; however, a few limited works have been successful in this regard. In most of the
Fig. 8. Kinetics of intra-particle diffusion model.
qe (mg/g) 0.546 qe (mg/g) 0.148 kid,2 (mg/g min) 1.66 C2 99.74
R2 0.74 R2 0.99 R12 0.99 R22 81
works the specific surface area of the adsorbents is much less than 2000 m2/g and in some limited works it reaches to the mentioned amount, although in such kind of works the mesopore volume is very low and microporosity is the dominant structure. Table S1 (see Supplementary material) lists some porous materials textural properties with high surface area reported by other researchers. Since all samples shown in Table S1 have microporous structure, it can be concluded that increasing surface area in many cases led to decreasing mesopore volume. In addition, total pore volume in all the samples is lower than that of GAC reported here. Mesoporous structure of GAC can be contributed to coating high porous structure of activated carbon by mesoporous graphene nanosheets [15]. The morphology of GAC shown by SEM image in Fig. 4 confirms that. In this structure, graphene nanosheets with thickness less than 5 nm lied on activated carbon and this phenomenon could lead to covering micropores.
Adsorption isotherms
Parameters Qm (mg/g) 217.6 kf (L/mg) 109.466
Freundlich isotherm
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3.2. Effect of stirring rate
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Stirring rate can affect the distribution of the solute in the bulk solution as well as the formation of the external boundary film [27]. Thus, various stirring rates (100, 200, 500 and 1000 rpm) were studied. The results showed that the effect of stirring rate on the adsorption of Pb(II) by GAC was insignificant. Higher stirring speed could slightly increase the initial adsorption rate but it became nullified with passage of time, and the equilibrium adsorption capacity of Pb(II) for all stirring speeds was almost the same.
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3.3. Effect of GAC dosage
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Different GAC doses (10–50 mg/10 mL) on adsorption of Pb(II) were analyzed at a constant concentration of lead ion solution (100 mg/L) under fixed parameters: pH 5 and contact time 4 h. The percentage of removal of Pb(II) increased from 70.35 to 94.84% (see Fig. 5). This can be explained as adsorbent dose increased, more and more surface area will be available which exposed more active sites for binding metal ions [28].
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3.4. Effect of pH on the adsorption
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The effects of pH on metal ions adsorption have been studied by many researchers previously, and the results indicated that pH of solution exerts a great effect on uptake of metal ions [29,30]. In order to investigate the effect of pH on the adsorption of Pb(II) onto
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Table 3 Results of adsorption data modeling using Langmuir and Freundlich models.
Langmuir isotherms
274 283 282 281 280 279 278 277 276 275
b (L/mg) 0. 08 1/n 0.312
RL 0.11 –
R2 0.99 R2 0.92
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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Fig. 9. Langmuir (a) and Freundlich (b) models fitting.
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GAC, a series of lead solutions containing single component at the same initial conditions (100 mg Pb(II)/L with 20 mg of GAC in 10 mL solutions at 298 K) were adjusted to a pH range of 2.0–6.0, then the batch experiments were conducted. Effect of pH on the adsorption of Pb(II) by GAC is shown in Fig. 6. It can be seen that the uptake of
Pb(II) by GAC is poor at pH < 3. The results can be explained based on the competition between Pb(II) and H3O+ for adsorption sites on GAC. At low pH levels, an excess H3O+ could compete with Pb(II), resulting in a low level of adsorbed Pb(II). With the pH increased, there are fewer hydrogen protons in solution, this means that there
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Table 4 Comparison of maximum adsorption capacities (Qm) of Pb(II) on different adsorbents. Adsorbent
Qm (mg/g)
References
Sludge biomass-based activated carbon Sugarcane bagasse-based activated carbon Hazelnut husk-based activated carbon Coconut shell-based activated carbon Peanut hull-based activated carbon Palm shell-based activated carbon Pecan shell-based activated carbon Algal waste-based activated carbon Date pit-based activated carbon Rice straw-based activated carbon Polygonum orientale Linn-based activated carbon CNT CNT Acidified CNT Zeolite Bare GO Bare ACG GAC
58 135 13.05 76.66 30.43 82.0 64.20 44.00 30.70 36.05 98.39 102 97 85 78.6 131.37 39.07 217.6
[49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [6] Present work Present work Present work
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are less competition of binding sites and more binding sites are released, the surface charges GAC become more negative, which causes electrostatic interactions and results in that the adsorption of Pb(II) increases dramatically in the range of pH value from 3.0 to 6.0. These results indicate that the adsorption of metal ions onto GAC depends highly on the pH of solution.
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3.5. Adsorption kinetics
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To study adsorption kinetics of GAC, the data related to adsorption capacity at time t (Fig. 7a) was used. The adsorption kinetics was modeled by means of the pseudo-first order and pseudo-second order models. GAC was found to follow the pseudosecond order model better than the pseudo-first order model (Fig. 7b and c and Table 2). It is elucidated that the adsorption kinetics depends greatly on the physical and/or chemical characteristics of the adsorbents [31]. In addition the pseudosecond order equation did describe the adsorption results of Pb(II) onto GAC adequately, with correlation coefficients of 0.99, which implies that the basic adsorption is chemisorptions, involving a sharing of electrons between the adsorbate and surface of the adsorbent [32] such as the Lewis acid sites and COxHy surface functional groups with acid properties [33]. Chemisorption is usually restricted to just one layer of molecules on the surface, although it may be followed by additional layers of physically adsorbed molecules [34].
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3.6. Intra-particle diffusion study
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The Weber–Morris equation was applied to investigate the intra-particle diffusion. The intra-particle diffusion is the sole ratelimiting step if the regression of qt against t1/2 is linear and passes through the origin [35]. However, multi-linearities can be observed in Fig. 8. The first, sharper portion was the external surface adsorption or the instantaneous adsorption. The second portion was the gradual adsorption stage where intraparticle diffusion was ratelimiting. Table 3 lists the corresponding model parameters based on the respective equation. For all initial concentrations, k1 was higher than k2 and C2 was larger than C1. This showed that the rate of Pb(II) removal was higher in the beginning because of large surface area of the adsorbent available for the adsorption of metal ions. After the adsorbed material formed a thick layer (caused by the interionic attraction and molecular association), the capacity of adsorbent got exhausted and the uptake rate was controlled by the rate at which the adsorbate was transported from the exterior to the interior sites of the adsorbent particles. None of the plots passed through the origin (Fig. 8), which revealed that the intraparticle diffusion was part of the adsorption but was not the only rate-controlling step. Some other mechanisms such as complexes or ion-exchange may also control the rate of adsorption [36,37].
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solution (100 mg/L, 10 mL, pH 5) and contacting time 240 min. Two mentioned models were fitted in Fig. 9a and b for Pb(II) adsorption on the GAC. The correlation coefficients (R2) for the above models (Table 3) show that the Langmuir model fitted better than Freundlich model. Therefore, Langmuir model can be used to best describe the Pb(II) adsorption behavior on the GAC. It can be deduced that Pb(II) adsorption process is mainly homogeneous and monolayer adsorption. In addition, RL < 1.0 (Table 3) is a further indication that Langmuir adsorption is dominant. In order to compare the adsorption capacity of Pb(II) on GAC, bare GO and ACG, the maximum adsorption capacities (Qm) of various adsorbents including activated carbon, CNT and zeolite are given in Table 4. Compared to other adsorbents including bare GO and ACG synthesized here, it is obvious that GAC’s adsorption capacity is higher than those of other adsorbents.
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4. Conclusion
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High surface area and mesoporous graphene/activated carbon composite was synthesized from graphene oxide and glucose. The samples were characterized by X-ray diffraction pattern, Raman spectroscopy, SEM image and nitrogen adsorption–desorption isotherms. The GAC’s surface area (2012 m2/g), total pore volume (1.61 cm3/g) and ratio of mesopore to total pore volume (0.61) revealed that the GAC can be considered as a promising adsorbent for removal of different pollutants from water. To study the adsorption behavior of Pb(II) on GAC, effects of pH, GAC dosage and stirring speed were studied. The results showed that the effect of stirring speed on adsorption of Pb(II) on GAC is insignificant; however solution pH played an important role in this regard. Adsorbent dosage also influenced the adsorption of Pb(II) significantly. In addition, the adsorption performance and capacity of the GAC for removal of Pb(II) from aqueous solution were studied by measuring adsorption kinetics and isotherms. The adsorption kinetics was modeled by means of the pseudo-first order and pseudo-second order models. The GAC was found to follow the pseudo-second order model better than the pseudo-first order model. In addition, the Weber–Morris equation was applied to investigate the intra-particle diffusion. It was concluded that the intraparticle diffusion was part of the adsorption but was not the only rate-controlling step. Langmuir and Freundlich equilibrium isotherms models were used to study the adsorption of Pb(II) under the certain conditions. The correlation coefficients for the above models showed that the Langmuir model fitted better than Freundlich model. Therefore, the Pb(II) adsorption on the GAC is mainly homogeneous and monolayer adsorption. A comparison between the maximum adsorption capacity of the GAC and several other porous materials including bare ACG and GO synthesized here disclosed that the GAC has higher maximum adsorption capacity (217 mg/g) to Pb(II) than other adsorbents.
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Appendix A. Supplementary data
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To optimize the use of adsorbents, adsorption isotherms are important criteria since they describe the nature of interaction between adsorbate and adsorbent. In addition, it is important to establish the most appropriate correlation for the equilibrium isotherms while optimizing the design of adsorption process to remove Pb(II) from solution. In this work, Langmuir and Freundlich equilibrium isotherms models were used to study the adsorption of Pb(II) under the conditions of adsorbent dose of 2 g/L, Pb(II)
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jece.2015.09.023.
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References
463
403 404 405 406 407 408 409
[1] H. Jabeen, K.C. Kemp, V. Chandra, Synthesis of nano zerovalent iron nanoparticles—graphene composite for the treatment of lead contaminated water, J. Environ. Manage. 130 (2013) 429–435, doi:http://dx.doi.org/10.1016/j. jenvman.2013.08.022.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
462
464 465 466
G Model
JECE 785 1–10 N. Saeidi et al. / Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx
467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513
514 515 516 517 518 519 520 521 522 523 524 525
[2] M.A.P. Cechinel, S.M.A.G. Ulson de Souza, A.A. Ulson de Souza, Study of lead(II) adsorption onto activated carbon originating from cow bone, J. Clean. Prod. 65 (2014) 342–349. [3] H.A. Aziz, M.N. Adlan, K.S. Ariffin, Heavy metals (Cd, Pb, Zn, Ni, Cu and Cr(III)) removal from water in Malaysia: post treatment by high quality limestone, Bioresour. Technol. 99 (6) (2008) 1578–1583, doi:http://dx.doi.org/10.1016/j. biortech.2007.04.007. [4] Y. Liu, J. Yan, D. Yuan, Q. Li, X. Wu, The study of lead removal from aqueous solution using an electrochemical method with a stainless steel net electrode coated with single wall carbon nanotubes, Chem. Eng. J. 218 (2013) 81–88, doi: http://dx.doi.org/10.1016/j.cej.2012.12.020. [5] Y. Huang, S. Li, J. Chen, X. Zhang, Y. Chen, Adsorption of Pb(II) on mesoporous activated carbons fabricated from water hyacinth using H3PO4 activation: adsorption capacity, kinetic and isotherm studies, Appl. Surf. Sci. (2014) , doi: http://dx.doi.org/10.1016/j.apsusc.2013.12.123. [6] S. Wang, T. Terdkiatburana, M.O. Tadé, Adsorption of Cu(II), Pb(II) and humic acid on natural zeolite tuff in single and binary systems, Sep. Purif. Technol. 62 (1) (2008) 64–70, doi:http://dx.doi.org/10.1016/j.seppur.2008.01.004. [7] A.A.H. Izzeldin, S.M. Bice, J. Catherine, O.N. Vincent, Adsorption studies of aqueous Pb(II) onto a sugarcane bagasse/multi-walled carbon nanotube composite, Phys. Chem. Earth 66 (2013) 157–166. [8] X. Deng, L. Lü, H. Li, F. Luo, The adsorption properties of Pb(II) and Cd(II) on functionalized graphene prepared by electrolysis method, J. Hazard. Mater. 183 (1–3) (2010) 923–930, doi:http://dx.doi.org/10.1016/j.jhazmat.2010.07.117. [9] G. Zhao, X. Ren, X. Gao, X. Tan, J. Li, C. Chen, Y. Huang, X. Wang, Removal of Pb(II) ions from aqueous solutions on few-layered graphene oxide nanosheets, Dalton Trans. 40 (41) (2011) 10945–10952, doi:http://dx.doi.org/10.1039/ c1dt11005e. [10] L. Cui, Y. Wang, L. Gao, L. Hu, L. Yan, Q. Wei, B. Du, EDTA functionalized magnetic graphene oxide for removal of Pb(II), Hg(II) and Cu(II) in water treatment: adsorption mechanism and separation property, Chem. Eng. J. 281 (2015) 1–10, doi:http://dx.doi.org/10.1016/j.cej.2015.06.043. [11] S. Luo, X. Xu, G. Zhou, C. Liu, Y. Tang, Y. Liu, Amino siloxane oligomer-linked graphene oxide as an efficient adsorbent for removal of Pb(II) from wastewater, J. Hazard. Mater. 274 (2014) 145–155, doi:http://dx.doi.org/10.1016/j. jhazmat.2014.03.062. [12] L. Hao, H. Song, L. Zhang, X. Wan, Y. Tang, Y. Lv, SiO2/graphene composite for highly selective adsorption of Pb(II) ion, J. Colloid Interface Sci. 369 (1) (2012) 381–387, doi:http://dx.doi.org/10.1016/j.jcis.2011.12.023. [13] G. Zhao, J. Li, X. Ren, C. Chen, X. Wang, Few-layered grapheme oxide nanosheets as superior sorbents for heavy metal ion pollution management, Environ. Sci. Technol. 45 (24) (2011) 10454–10462, doi:http://dx.doi.org/10.1021/ es203439v. [14] Z. Huang, X. Zheng, W. Lv, M. Wang, Q. Yang, F. Kang, Adsorption of lead (II) Ions from aqueous solution on low-temperature exfoliated grapheme nanosheets, Langmuir 27 (12) (2011) 7558–7562. [15] C. Zheng, X. Zhou, H. Cao, G. Wang, Z. Liu, Synthesis of porous graphene/ activated carbon composite with high packing density and large specific surface area for supercapacitor electrode material, J. Power Sources 258 (2014) 290–296, doi:http://dx.doi.org/10.1016/j.jpowsour.2014.01.056. [16] L. Jiang, J. Yan, Y. Zhou, L. Hao, R. Xue, L. Jiang, B. Yi, Activated carbon/graphene composites with high-rate performance as electrode materials for electrochemical capacitors, J. Solid State Electrochem. 17 (11) (2013) 2949–2958, doi: http://dx.doi.org/10.1007/s10008-013-2217-x. [17] W.S. Hummers, R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80 (6) (1958) 1339, doi:http://dx.doi.org/10.1021/ja01539a017. [18] C. Xu, J. Sun, L. Gao, Synthesis of novel hierarchical graphene/polypyrrole nanosheet composites and their superior electrochemical performance, J. Mater. Chem. 21 (30) (2011) 11253–11258, doi:http://dx.doi.org/10.1039/ c1jm11275a. [19] N. Saeidi, M. Parvini, M.R. Sarsabili, Studying performance of Dubinin–Astakhov and Dubinin–Raduchkevic equations to evaluate nanopore volume and pore size of MCM-41 particles, IJE Trans. A 27 (2014) 1511–1518. [20] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 40 (9) (1918) 1361–1403, doi:http://dx.doi.org/ 10.1021/ja02242a004. [21] H. Freundlich, Adsorption in solution, Phys. Chem. Soc. 40 (1906) 1361–1368. [22] T.W. Weber, R.K. Chakravorti, Pore and solid diffusion models for fixed bed adsorbers, AIChE J. 20 (2) (1974) 228–238, doi:http://dx.doi.org/10.1002/ aic.690200204. [23] M.H. Kalavathy, T. Karthikeyan, S. Rajgopal, L.R. Miranda, Kinetic and isotherm studies of Cu(II) adsorption onto H3PO4-activated rubber wood sawdust, J. Colloid Interface Sci. 292 (2) (2005) 354–362, doi:http://dx.doi.org/10.1016/j. jcis.2005.05.087. [24] W.J. Weber, J.R. Moris, Kinetics of adsorption on carbon from solution, J. San. Eng. Div. ASCE Civil Eng. 89 (1963) 31–39. [25] O.C. Compton, S.T. Nguyen, Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials, Small 6 (6) (2010) 711–723, doi:http://dx.doi.org/10.1002/smll.200901934. [26] Y. Chen, X. Zhang, H. Zhang, X. Sun, D. Zhang, Y. Ma, High-performance supercapacitors based on a graphene-activated carbon composite prepared by chemical activation, RSC Adv. 2 (20) (2012) 7747–7753, doi:http://dx.doi.org/ 10.1039/c2ra20667f. [27] M.K. Aroua, S.P.P. Leong, L.Y. Teo, C.Y. Yin, W.M.A.W. Daud, Real-time determination of kinetics of adsorption of lead(II) onto palm shell-based activated
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
9
carbon using ion selective electrode, Bioresour. Technol. 99 (13) (2008) 5786– 5792. P.L. Homagai, K.N. Ghimire, K. Inoue, Adsorption behavior of heavy metals onto chemically modified sugarcane bagasse, Bioresour. Technol. 101 (6) (2010) 2067–2069, doi:http://dx.doi.org/10.1016/j.biortech.2009.11.073. D. Xu, X. Tan, C. Chen, X. Wang, Removal of Pb(II) from aqueous solution by oxidized multiwalled carbon nanotubes, J. Hazard. Mater. 154 (1–3) (2008) 407–416, doi:http://dx.doi.org/10.1016/j.jhazmat.2007.10.059. G.P. Rao, C. Lu, F. Su, Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review, Sep. Purif. Technol. 58 (1) (2007) 224–231, doi: http://dx.doi.org/10.1016/j.seppur.2006.12.006. A.E. Ofomaja, E.I. Unuabonah, N.A. Oladoja, Competitive modeling for the biosorptive removal of copper and lead ions from aqueous solution by Mansonia wood sawdust, Bioresour. Technol. 101 (11) (2010) 3844–3852, doi: http://dx.doi.org/10.1016/j.biortech.2009.10.064. H. Lu, W. Zhang, Y. Yang, X. Huang, S. Wang, R. Qiu, Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar, Water Res. 46 (3) (2012) 854–862, doi:http://dx.doi.org/10.1016/j.watres.2011.11.058. F. Di Natale, A. Erto, A. Lancia, D. Musmarra, Mercury adsorption on granular activated carbon in aqueous solutions containing nitrates and chlorides, J. Hazard. Mater. 192 (3) (2011) 1842–1850, doi:http://dx.doi.org/10.1016/j. jhazmat.2011.07.021. E.N. El Qada, S.J. Allen, G.M. Walker, Adsorption of methylene blue onto activated carbon produced from steam activated bituminous coal: a study of equilibrium adsorption isotherm, Chem. Eng. J. 124 (1–3) (2006) 103–110, doi: http://dx.doi.org/10.1016/j.cej.2006.08.015. A. Mittal, A. Malviya, D. Kaur, J. Mittal, L. Kurup, Studies on the adsorption kinetics and isotherms for the removal and recovery of methyl orange from wastewaters using waste materials, J. Hazard. Mater. 148 (1–2) (2007) 229– 240, doi:http://dx.doi.org/10.1016/j.jhazmat.2007.02.028. F.C. Wu, R.L. Tseng, R.S. Juang, Comparisons of porous and adsorption properties of carbons activated by steam and KOH, J. Colloid Interface Sci. 283 (1) (2005) 49–56, doi:http://dx.doi.org/10.1016/j.jcis.2004.08.037. W.H. Cheung, Y.S. Szeto, G. McKay, Intraparticle diffusion processes during acid dye adsorption onto chitosan, Bioresour. Technol. 98 (15) (2007) 2897–2904, doi:http://dx.doi.org/10.1016/j.biortech.2006.09.045. D. Angin, Production and characterization of activated carbon from sour cherry stones by zinc chloride, Fuel 115 (2014) 804–811, doi:http://dx.doi.org/ 10.1016/j.fuel.2013.04.060. X. Ma, F. Zhang, J. Zhu, L. Yu, X. Liu, Preparation of highly developed mesoporous activated carbon fiber from liquefied wood using wood charcoal as additive and its adsorption of methylene blue from solution, Bioresour. Technol. 164 (2014) 1–6, doi:http://dx.doi.org/10.1016/j.biortech.2014.04.050. T.H. Liou, Development of mesoporous structure and high adsorption capacity of biomass-based activated carbon by phosphoric acid and zinc chloride activation, Chem. Eng. J. 158 (2) (2010) 129–142, doi:http://dx.doi.org/10.1016/j. cej.2009.12.016. R.L. Tseng, S.K. Tseng, Pore structure and adsorption performance of the KOHactivated carbons prepared from corncob, J. Colloid Interface Sci. 287 (2) (2005) 428–437, doi:http://dx.doi.org/10.1016/j.jcis.2005.02.033. M. Olivares-Marín, C. Fernández-González, A. Macías-García, V. Gómez-Serrano, Preparation of activated carbon from cherry stones by chemical activation with ZnCl2, Appl. Surf. Sci. 252 (17) (2006) 5967–5971, doi:http://dx.doi. org/10.1016/j.apsusc.2005.11.008. S. Yorgun, N. Vural, H. Demiral, Preparation of high-surface area activated carbons from Paulownia wood by ZnCl2 activation, Micropor. Mesopor. Mater. 122 (1–3) (2009) 189–194, doi:http://dx.doi.org/10.1016/j.micromeso.2009.02.032. J. Srenscek-Nazzal, W. Kaminska, B. Michalkiewicz, Z.C. Koren, Production, characterization and methane storage potential of KOH-activated carbon from sugarcane molasses, Ind. Crops Prod. 47 (2013) 153–159, doi:http://dx.doi.org/ 10.1016/j.indcrop.2013.03.004. A. Minoda, S. Oshima, H. Iki, E. Akiba, Synthesis of KOH-activated porous carbon materials and study of hydrogen adsorption, J. Alloys Compd. 580 (2013) S301–S304, doi:http://dx.doi.org/10.1016/j.jallcom.2013.02.085. E. Raymundo-Piñero, P. Azaïs, T. Cacciaguerra, D. Cazorla-Amorós, A. LinaresSolano, F. Béguin, KOH and NaOH activation mechanisms of multiwalled carbon nanotubes with different structural organization, Carbon 43 (4) (2005) 786–795, doi:http://dx.doi.org/10.1016/j.carbon.2004.11.005. N. Ferrera-Lorenzo, E. Fuente, I. Suárez-Ruiz, Ruiz, B., KOH activated carbon from conventional and microwave heating system of a macroalgae waste from the agar–agar industry, Fuel Process. Technol. 121 (2014) 25–31. T. Mitome, Y. Uchida, Y. Egashira, K. Hayashi, A. Nishiura, N. Nishiyama, Adsorption of indole on KOH-activated mesoporous carbon, Colloids Surf. A Physicochem. Eng. Aspects 424 (2013) 89–95, doi:http://dx.doi.org/10.1016/j. colsurfa.2013.02.022. E. Kusvuran, D. Yildirim, A. Samil, O. Gulnaz, A study: removal of Cu(II), Cd(II), and Pb(II) ions from real industrial water and contaminated water using activated sludge biomass, Clean 40 (11) (2012) 1273–1283, doi:http://dx.doi. org/10.1002/clen.201100443. H.C. Tao, H.R. Zhang, J.B. Li, W.Y. Ding, Biomass based activated carbon obtained from sludge and sugarcane bagasse for removing lead ion from wastewater, Bioresour. Technol. 192 (2015) 611–617, doi:http://dx.doi.org/10.1016/j.biortech.2015.06.006.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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[51] M. Imamoglu, O. Tekir, Removal of copper (II) and lead (II) ions from aqueous solutions by adsorption on activated carbon from a new precursor hazelnut husks, Desalination 228 (1–3) (2008) 108–113. [52] Y. Kikuchi, Q. Qian, M. Machida, H. Tatsumoto, Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution, Carbon 44 (2) (2006) 195–202, doi:http://dx.doi.org/10.1016/j.carbon.2005.07.040. [53] P. Brown, I.A. Atly Jefcoat, D. Parrish, S. Gill, E. Graham, Evaluation of the adsorptive capacity of peanut hull pellets for heavy metals in solution, Adv. Environ. Res. 4 (1) (2000) 19–29, doi:http://dx.doi.org/10.1016/S1093-0191 (00)00004-6. [54] G. Issabayeva, M.K. Aroua, N.M.N. Sulaiman, Removal of lead from aqueous solutions on palm shell activated carbon, Bioresour. Technol. 97 (18) (2006) 2350–2355, doi:http://dx.doi.org/10.1016/j.biortech.2005.10.023. [55] R.R. Bansode, J.N. Losso, W.E. Marshall, R.M. Rao, R.J. Portier, Adsorption of metal ions by pecan shell-based granular activated carbons, Bioresour. Technol. 89 (2) (2003) 115–119, doi:http://dx.doi.org/10.1016/S0960-8524(03) 00064-6. [56] V.J.P. Vilar, C.M.S. Botelho, R.A.R. Boaventura, Boaventura, Influence of pH, ionic strength and temperature on lead biosorption by Gelidium and agar extraction algal waste, Proc. Biochem. 40 (10) (2005) 3267–3275, doi:http://dx.doi.org/ 10.1016/j.procbio.2005.03.023.
[57] M. Abdulkarim, F.A. Al-Rub, Adsorption of lead ions from aqueous solution onto activated carbon and chemically-modified activated carbon prepared from date pits, Adsorp. Sci. Technol. 22 (2004) 119–134. [58] M.M. Johns, W.E. Marshall, C.A. Toles, Agricultural by-products as granular activated carbons for adsorbing dissolved metals and organics, J. Chem. Technol. Biotechnol. 71 (2) (1998) 131–140, doi:http://dx.doi.org/10.1002/ (SICI)1097-4660(199802)71:2<131::AID-JCTB821>3.0.CO;2-K. [59] L. Wang, J. Zhang, R. Zhao, Y. Li, C. Li, C. Zhang, Adsorption of Pb(II) on activated carbon prepared from Polygonum orientale Linn.: kinetics, isotherms, pH, and ionic strength studies, Bioresour. Technol. 101 (15) (2010) 5808–5814, doi: http://dx.doi.org/10.1016/j.biortech.2010.02.099. [60] N.A. Kabbashi, M.A. Atieh, A. Al-Mamun, M.E. Mirghami, M.D.Z. Alam, N. Yahya, Kinetic adsorption of application of carbon nanotubes for Pb(II) removal from aqueous solution, J. Environ. Sci. 21 (4) (2009) 539–544, doi:http://dx.doi.org/ 10.1016/S1001-0742(08)62305-0. [61] Y.H. Li, J. Ding, Z. Luan, Z. Di, Y. Zhu, C. Xu, D. Wu, B. Wei, Competitive adsorption of Pb2+, Cu2+ and Cd2+ ions from aqueous solutions by multiwalled carbon nanotubes, Carbon 41 (14) (2003) 2787–2792, doi:http://dx.doi.org/ 10.1016/S0008-6223(03)00392-0. [62] H.J. Wang, A.L. Zhou, F. Peng, H. Yu, L.F. Chen, Adsorption characteristic of acidified carbon nanotubes for heavy metal Pb(II) in aqueous solution, Mater. Sci. Eng. A 466 (1–2) (2007) 201–206, doi:http://dx.doi.org/10.1016/j. msea.2007.02.097.
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Contents lists available at ScienceDirect
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High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb(II) from wastewater
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Navid Saeidi* , Mehdi Parvini, Zahra Niavarani
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Faculty of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan 35195-363, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 August 2015 Received in revised form 27 September 2015 Accepted 28 September 2015 Available online xxx
Since lead is a carcinogenic and non-biodegradable substance, its removal from water is of vital importance. Of all different removal pollutants techniques the adsorption is a promising method to remove Pb(II). The choice of adsorbent is a key factor to carry out this process efficiently. As already the adsorption of Pb(II) onto different porous materials have been studied, however the adsorption properties of graphene/activated carbon composite (GAC) to metal ions have not been reported yet. In this work, GAC was synthesized from graphene oxide and glucose. The samples were characterized by Xray diffraction, Raman spectroscopy, SEM image and N2 adsorption–desorption isotherms. The GAC possessed high surface area (2012 m2/g), large pore volume (1.61 cm3/g) and mesopore structure. To study the adsorption behavior of Pb(II) on GAC, effects of solution pH, GAC dosage and stirring speed were examined. Afterwards the adsorption isotherms and kinetics of the GAC for removal of Pb(II) were studied by different models. The GAC was found to follow the pseudo-second order kinetic model better than the pseudo-first order. In addition it was understood that the intraparticle diffusion which studied by the Weber–Morris equation addressed the mechanism of the adsorption properly. Since the adsorption isotherm experimental data was fitted better by Langmuir model than Freundlich, the Pb(II) adsorption on the GAC is mainly homogeneous and monolayer. Finally, the maximum adsorption capacity of Pb(II) was measured up to 217 mg/g, which is higher than many other adsorbents. ã 2015 Published by Elsevier Ltd.
Keywords: Graphene Activated carbon composite Mesoporous Pb(II) Adsorption kinetics and isotherms
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1. Introduction
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Lead(II) is a serious environmental health threat because of its non-biodegradability, toxicity, wide-spread presence and tendency to accumulate in living organisms. It can damage nervous system and cause renal kidney disease, mental retardation, cancer and anemia in humans. Water systems are polluted by lead ions in various ways, including mining, painting and printing processes, plumbing, automobile batteries and petroleum industries [1]. As a priority contaminant, the EPA has set a permissible limit of 0.015 mg/L in drinking water [2]. Various methods have been proposed for the treatment of leadcontaminated water such as chemical precipitation [3], electrochemical reduction [4] and ion exchange [1]. However, confinements of these treatment processes appear by virtue of high operational cost, low treatment efficiency and secondary problems from generation of metal-bearing toxic sludge [5]. Among these methods, adsorption is a promising one as it is more efficient, economical and easier to handle than other
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treatment methods. Many researches for adsorption removal of heavy metals including Pb(II) ions have been reported in the literature [1–3,6–8] however, search for adsorbents with high adsorption capacities is still in great need. It means that the choice of adsorbent when attempting to isolate Pb(II) is of special importance. In the past, apart from activated carbon (AC) which has been a traditional adsorbent for different pollutants, the adsorption of Pb (II) onto zeolites [6], CNT [7], graphene [8], graphene oxide (GO) [9] and different graphene based materials such as functionalized magnetic graphene oxide [10], amino siloxane oligomer-linked graphene oxide [11] and SiO2/graphene composite [12] has been researched extensively; however, the adsorption properties of graphene/activated carbon composite (GAC) for metal ions have not been reported yet. GO has been demonstrated to have a very high adsorption capacity in the removal of Pb(II), Cd(II), and Co(II) from aqueous solutions [9,13,14]. The oxygen containing functional groups on the surfaces of GO played important roles in the metal ions sorption. In
* Corresponding author. Fax: +98 231 3354120. E-mail address: [email protected] (N. Saeidi). http://dx.doi.org/10.1016/j.jece.2015.09.023 2213-3437/ ã 2015 Published by Elsevier Ltd.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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graphene/activated carbon composite, AC is annealed with GO. In the composite, a layer of porous AC is coated on graphene sheets, which not only inhibits agglomeration and increases surface area, but also enhances mesoporosity. In other words, chemically modified graphene is ideal filler for the microporous carbon due to its high mesoporous structure. Comparing to large AC particles, it is worth pointing out that the nanosheet composite will reduce the adsorption pathway significantly [15,16]. In this work, high surface area and mesoporous GAC was synthesized by means of GO and glucose as precursor and through a two-step activation method. Then, the resultant GAC was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherms. Afterwards, the adsorption isotherms and kinetics of Pb (II) onto the GAC were studied.
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2. Materials and methods
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2.1. Chemicals
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All chemicals were analytical reagents with mass fraction purity greater than 0.99 and were used without any further purification. All solutions were prepared using deionized water. The pH of working solutions were adjusted with 10% (wt/wt) NaOH and 10% (vol.:vol.) HNO3.
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2.2. Synthesis and purification of GO
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GO powder used in this work was obtained from chemical exfoliation of natural graphite using NaNO3, H2SO4, and KMnO4 following a modified Hummers method [17,18]. The procedure was as follows: 2 g of graphite and 2 g of NaNO3 were placed in a flask and 92 mL of concentrated H2SO4 was added with constant stirring, followed by the slow addition of 12 g of KMnO4 in an ice-water bath. The solution was stirred for 3 h, and the reaction flask was then transferred to a water bath at 30 C and stirred for another 4 h. Next, 200 mL of water was added and the temperature of the suspension was maintained at 95 C for 30 min. Then, 20 mL of H2O2 (30%) was added, whereupon the solution changed color from brown to yellow. After centrifugation at 7000 rpm for 15 min, the solid phase was washed three times with 0.1 M HCl. The sample was then rinsed with deionized water until the pH of the solution was neutral. The desired products were exfoliated using powerful ultrasonication and then were dried under vacuum for 24 h to obtain dark brown GO powder.
85
2.3. Synthesis of GAC
69 70 71 72 73 74 75 76 77 78 79 80 81 82 83
86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
Firstly, 0.15 g of obtained GO powder was added into 100 mL of deionized water and then dispersed by ultrasonication with power of 300 W for 60 min, resulting in an inhomogeneous yellow–brown dispersion. Afterwards, 10 g glucose was added to the dispersion gradually during 5 h ultrasonic bath (80 W). Then, the solvent was vaporized at 60 C in the oven overnight. The dried powder was heated up to 350 C under N2 flow at the rate of 2 C/min in a tubular furnace and held at the temperature for 2 h. For further activation, the obtained carbonized powder underwent a two-step chemical activation. In first step, the powder and ZnCl2 as activating agent with impregnation ration of 1–2, respectively, were added into 100 mL deionized water and agitated for 7 h at 60 C. In fact, ZnCl2 was used to create porosity in the carbonized powder. Evaporation during this time was avoided using a close-up glass container. Then the supernatant solution was separated by vacuum filtration and the remaining solid was oven-dried at 90 C for 2 h. The impregnated sample was placed on a quartz dish, which was then inserted in a quartz tube. The impregnated sample
was heated up to activation temperature (400 C) under N2 flow at the rate of 10 C/min and held at the activation temperature for 1 h. The resulting solids were boiled at about 90 C with 100 mL of 1 M HCl solution for 30 min to leach out the remaining ZnCl2, then filtered and rinsed by warm distilled water several times to remove the excess agent. They were then dried at 100 C for 12 h. The second step was carried out the same as the first one with some alterations as follows: arranging weight ratio of the resultant powder to KOH up to 1–3, soaking for 1 h at 50 C, activating at 750 C under N2 flow at the rate of 10 C/min and holding at the activation temperature for 1 h. KOH played the role of activating agent in the second step. Actually it was used to boost the surface area of the resultant composite. The obtained composite was denoted as GAC.
104
2.4. Synthesis of AC from glucose
118
Glucose was dried and then carbonized under N2 flow in a tubular furnace at 350 C for 5 h. For further activation, the resultant black powder was impregnated with KOH (KOH/carbon mass ratio 4:1) for 8 h under continuous agitation. Afterwards, it was heated up to 800 C under N2 flow at the rate of 5 C/min and kept at the temperature for 1 h. Then, the sample was washed by boiled deionized water several times and dried at 100 C overnight. The AC prepared from glucose was named as ACG.
119
2.5. Structural characteristics
127
The XRD patterns were obtained by using a PW1840 diffractometer employing Cu Ka radiation (l = 1.54056 Å), u –2u geometry and a scintillation detector. Each diffraction pattern was recorded at a step of 0.04 and 0.5 s per step. The measurements were made at ambient condition. Raman spectroscopy plots were obtained by a Handheld Raman Analyzer (FirstguardTM, Rigaku). A morphological characterization of GAC was carried out with a scanning electron microscope (MIRA//TESCAN). The sample was placed on a sample holder with an adhesive carbon foil and then the sample was then laid under a vacuum at room temperature. It was coated with gold before the examination. The nitrogen adsorption and desorption isotherms for the sample was measured at 196 C on a Belsorp 18 (BEL Japan, Ltd.). The sample was heated at 200 C for 3 h and degassed overnight. The specific surface area was determined by the Brunauer– Emmet–Teller (BET) method using am (N2 = 16.2 Å2), where am is the molecular area of nitrogen at 196 C. The BET formula is valid over a range of N2 relative partial pressure p/p0 varying from 0.01 to 0.30 [19]. Accordingly, the BET surface area of the sample was calculated on the mentioned range of relative partial pressure. The mesopore volume and the pore size distribution of GAC were determined based on BJH method. The total pore volume, Vtotal, was obtained using the adsorbed nitrogen at a relative pressure p/p0 of approximately 0.99.
128
105 106 107 108 109 110 111 112 113 114 115 116 117
120 121 122 123 124 125 126
129
Q2 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152
2.6. Adsorption experiments
153
The adsorption isotherms were carried out in fixed volumes of pollutant solution (10 mL) at 30 C and pH 5, for 4 h to reach the adsorption equilibrium, using a temperature-controlled shaker operated at 200 rpm. The solutions were prepared by diluting lead nitrate with deionized water (100 mg/L, 10 mL, pH 5). Then, the adsorption capacities were determined by atomic absorption spectrophotometry using a PerkinElmer 2380 instrument. All experiments were performed in duplicate at least and mean values were presented.
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Fig. 1. XRD diffraction patterns of GO and GAC.
163 164
165 166
The Pb(II) uptake at the equilibrium qe (mg/g) and removal efficiency (E%) were calculated as follows: qe ¼
ðC 0 C e ÞV m
ð1Þ
E% ¼
C0 Ce 100 C0
ð2Þ
where C0 and Ce (mg/L) are the initial and equilibrium concentrations of Pb(II), respectively; V (L) is the volume of the solution; and m (g) is the dosage of the adsorbent.
Fig. 2. Raman spectra of GO and GAC.
Fig. 3. N2 adsorption isotherm data of GAC (a) and GO (b) as well as pore size distribution of GAC (c).
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Table 1 Structural characteristics of GO, GAC and ACG. Sample
Surface area (m2/g)
Mean pore diameter (nm)
Vmeso
Vtotal
Vmeso/Vtotal
GO GAC ACG
85 2012 660
17.5 3.3 4.3
0.3 1.01 0.40
0.34 1.61 0.72
0.88 0.63 0.55
2.7. Adsorption isotherms
167
2.7.1. The Freundlich and Langmuir isotherms are represented by the following equations: Langmuir isotherm [20]
168
qe ¼
Q m bC e ð1 þ bC e Þ
ð3Þ
where Ce (mg/L) and qe (mg/g) are the equilibrium concentrations of Pb(II) in the liquid and solid phases, respectively; Qm and b are Langmuir constants. Qm is the maximum metal uptake (mg/g), whereas b is adsorption equilibrium constant (L/g) and related to the energy of adsorption. Freundlich isotherm [21] qe ¼ kf C 1=n e
Fig. 4. SEM image of GAC.
Fig. 5. Effect of GAC dosage on adsorption of Pb(II).
1 1 þ bC 0
171 172 173 174 175
ð4Þ
in which qe (mg/g) and Ce (mg/L) are the equilibrium concentrations of Pb(II) in the adsorbed and liquid phases, kf and n are the Freundlich constants, indicating the adsorption capacity and adsorption intensity. To determine whether the adsorption is favorable, a dimensionless constant separation factor or equilibrium parameter RL is defined based on the following equation [22]: RL ¼
169
Q3 170
177 176 178 179 180 181 182 183
ð5Þ
where b (L/mg) is the Langmuir isotherm constant, and C0 (mg/L) is the initial Pb(II) concentration. The RL value indicates whether the type of the isotherm is favorable (0 < RL < 1), unfavorable (RL > 1), linear (RL = 1), or irreversible (RL = 0).
Fig. 6. Effect of pH on the adsorption of Pb(II) by GAC.
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2.8. Adsorption kinetics
190
The pseudo-first order model was used to analyze the adsorption kinetics. The non-linear pseudo-first order model is expressed as [23]:
191 192
qt ¼ qe ð1 ek1 t Þ 193
195
q2e k2 t ð1 þ qe k2 tÞ
200 201 202 203
ð9Þ
where qt (mg/g) and qe (mg/g) are the adsorption capacity at time t (min) and at equilibrium, respectively, while k1 (min1) and k2 (min1) are the pseudo-first-order and pseudo-second-order rate constant, respectively. The intra-particle diffusion model (Weber–Morris equation) is expressed as [24]: qt ¼ kid t1=2 þ C
205 204 206
ð8Þ
This equation can be linearized in logarithmic form as: t 1 ¼ qt ðk2 q2e Þ
198 197 199
ð7Þ
The pseudo-second order model was also used to the same purpose. The non-linear form of this model is as follows: qt ¼
196
ð6Þ
This equation can be linearized in logarithmic form as: ½ðq qt Þ ¼ k1 t ln e qe
194
ð10Þ
207
where kid (mg/g min) is the intra-particle diffusion rate constant, and C (mg/g) is the constant proportional to the extent of boundary layer thickness.
208
3. Results and discussion
209
3.1. Characterization of GAC
210
As shown in Fig. 1, The XRD pattern of GO showed a sharp peak at about 12 , corresponding to interlayer spacing of 0.85 nm, and no obvious peak at the position of the (0 0 2) peak of graphite (about 26 ) is observed, indicating that the graphite has been fully expanded and successfully oxidized into graphite oxide. After activation and thermal treatment, the sharp diffraction peak of GO vanished, instead a weak and broad peak at 2u = 26 appeared. It can be contributed to the decreasing of the D-spacing value caused by removing most oxygen-functional groups intercalated into spacing of graphite the interlayer during thermal carbonization and reducing the particle size of composite during chemical activation steps [25]. The Raman spectra of GO and GAC are shown in Fig. 2, displaying both two characteristic D and G bands of chemically modified graphene. The Raman spectrum of GO displays a D-band at approximately 1354 cm1 and G-band at about 1615 cm1. The G-band originates from the in-phase vibration of the graphite lattice, while the D-band mainly comes from the structure defects created by the attachment of oxygen functional groups on the carbon basal plane. The D:G intensity ratio of GO is 0.81, indicating the high oxidation degree and/or relatively small domain size. After activation steps and thermal treatment, this ratio was remarkably increased to 1.25. This could be caused by the creation of defects of the sample [25,26]. The N2 adsorption isotherm data of GAC are shown in Fig. 3a. Adsorption measurements were followed by desorption measurements under the same conditions. This isotherm is a combination of type I and IV based on the IUPAC classification and is typical of
211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237
5
Fig. 7. Kinetics data of Pb(II) onto GAC (a), kinetic modeling of pseudo-first-order model (b) and pseudo-second-order model (c) of Pb(II) adsorption.
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Table 2 Parameters of the kinetic models for Pb(II) adsorption by GAC. Pseudo-first order model
Parameters
Pseudo-first order model
k1 (min1) 0.005 k1 (min1) 0.007 kid,1 (mg/g min) 14.6 C1 3.71
Pseudo-second order model Intra-particle diffusion model (Weber–Morris)
238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260
261 262 263 264 265 266 267 268 269 270 271 272 273
mesoporous materials with contributions of microporosity. On the contrary, the isotherm of GO (Fig. 3b) is a type IV which shows very low volume of nitrogen uptake compared with GAC. In these materials, capillary condensation normally takes place, leading to hysteresis loops. Micropore filling occurs at very low relative pleasures. From the N2 adsorption–desorption isotherms it was clear that the adsorbed volume increases with increasing p/p0, indicating the wider pore size distribution. The pore size distribution of GAC illustrates in Fig. 3c . The graph reveals that the sample has a well-defined pore structure presenting high mesoporosity (1–25 nm) with ignorable contributions of macroporosity (>25 nm). Table 1 summarizes the textural properties of GAC, GO and ACG. It can be seen that the surface area of GAC is 2012 m2/g, which is close to the theoretical value of graphene (2630 m2/g) and far more than that of thermally reduced graphene reported in other works. As mentioned above, GAC possesses not only very high surface area but also it has mesopore structure and high pore volume. This feature is very useful in different applications including waste water treatment. Many researchers have tried to improve both surface area and mesoporosity of porous materials, in particular activated carbon, simultaneously; however, a few limited works have been successful in this regard. In most of the
Fig. 8. Kinetics of intra-particle diffusion model.
qe (mg/g) 0.546 qe (mg/g) 0.148 kid,2 (mg/g min) 1.66 C2 99.74
R2 0.74 R2 0.99 R12 0.99 R22 81
works the specific surface area of the adsorbents is much less than 2000 m2/g and in some limited works it reaches to the mentioned amount, although in such kind of works the mesopore volume is very low and microporosity is the dominant structure. Table S1 (see Supplementary material) lists some porous materials textural properties with high surface area reported by other researchers. Since all samples shown in Table S1 have microporous structure, it can be concluded that increasing surface area in many cases led to decreasing mesopore volume. In addition, total pore volume in all the samples is lower than that of GAC reported here. Mesoporous structure of GAC can be contributed to coating high porous structure of activated carbon by mesoporous graphene nanosheets [15]. The morphology of GAC shown by SEM image in Fig. 4 confirms that. In this structure, graphene nanosheets with thickness less than 5 nm lied on activated carbon and this phenomenon could lead to covering micropores.
Adsorption isotherms
Parameters Qm (mg/g) 217.6 kf (L/mg) 109.466
Freundlich isotherm
284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299
3.2. Effect of stirring rate
300
Stirring rate can affect the distribution of the solute in the bulk solution as well as the formation of the external boundary film [27]. Thus, various stirring rates (100, 200, 500 and 1000 rpm) were studied. The results showed that the effect of stirring rate on the adsorption of Pb(II) by GAC was insignificant. Higher stirring speed could slightly increase the initial adsorption rate but it became nullified with passage of time, and the equilibrium adsorption capacity of Pb(II) for all stirring speeds was almost the same.
301
3.3. Effect of GAC dosage
309
Different GAC doses (10–50 mg/10 mL) on adsorption of Pb(II) were analyzed at a constant concentration of lead ion solution (100 mg/L) under fixed parameters: pH 5 and contact time 4 h. The percentage of removal of Pb(II) increased from 70.35 to 94.84% (see Fig. 5). This can be explained as adsorbent dose increased, more and more surface area will be available which exposed more active sites for binding metal ions [28].
310
3.4. Effect of pH on the adsorption
317
The effects of pH on metal ions adsorption have been studied by many researchers previously, and the results indicated that pH of solution exerts a great effect on uptake of metal ions [29,30]. In order to investigate the effect of pH on the adsorption of Pb(II) onto
318
Table 3 Results of adsorption data modeling using Langmuir and Freundlich models.
Langmuir isotherms
274 283 282 281 280 279 278 277 276 275
b (L/mg) 0. 08 1/n 0.312
RL 0.11 –
R2 0.99 R2 0.92
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311 312 313 314 315 316
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Fig. 9. Langmuir (a) and Freundlich (b) models fitting.
322 323 324 325 326
GAC, a series of lead solutions containing single component at the same initial conditions (100 mg Pb(II)/L with 20 mg of GAC in 10 mL solutions at 298 K) were adjusted to a pH range of 2.0–6.0, then the batch experiments were conducted. Effect of pH on the adsorption of Pb(II) by GAC is shown in Fig. 6. It can be seen that the uptake of
Pb(II) by GAC is poor at pH < 3. The results can be explained based on the competition between Pb(II) and H3O+ for adsorption sites on GAC. At low pH levels, an excess H3O+ could compete with Pb(II), resulting in a low level of adsorbed Pb(II). With the pH increased, there are fewer hydrogen protons in solution, this means that there
327 328 329 330 331
Table 4 Comparison of maximum adsorption capacities (Qm) of Pb(II) on different adsorbents. Adsorbent
Qm (mg/g)
References
Sludge biomass-based activated carbon Sugarcane bagasse-based activated carbon Hazelnut husk-based activated carbon Coconut shell-based activated carbon Peanut hull-based activated carbon Palm shell-based activated carbon Pecan shell-based activated carbon Algal waste-based activated carbon Date pit-based activated carbon Rice straw-based activated carbon Polygonum orientale Linn-based activated carbon CNT CNT Acidified CNT Zeolite Bare GO Bare ACG GAC
58 135 13.05 76.66 30.43 82.0 64.20 44.00 30.70 36.05 98.39 102 97 85 78.6 131.37 39.07 217.6
[49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [6] Present work Present work Present work
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are less competition of binding sites and more binding sites are released, the surface charges GAC become more negative, which causes electrostatic interactions and results in that the adsorption of Pb(II) increases dramatically in the range of pH value from 3.0 to 6.0. These results indicate that the adsorption of metal ions onto GAC depends highly on the pH of solution.
358
3.5. Adsorption kinetics
359
To study adsorption kinetics of GAC, the data related to adsorption capacity at time t (Fig. 7a) was used. The adsorption kinetics was modeled by means of the pseudo-first order and pseudo-second order models. GAC was found to follow the pseudosecond order model better than the pseudo-first order model (Fig. 7b and c and Table 2). It is elucidated that the adsorption kinetics depends greatly on the physical and/or chemical characteristics of the adsorbents [31]. In addition the pseudosecond order equation did describe the adsorption results of Pb(II) onto GAC adequately, with correlation coefficients of 0.99, which implies that the basic adsorption is chemisorptions, involving a sharing of electrons between the adsorbate and surface of the adsorbent [32] such as the Lewis acid sites and COxHy surface functional groups with acid properties [33]. Chemisorption is usually restricted to just one layer of molecules on the surface, although it may be followed by additional layers of physically adsorbed molecules [34].
360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375
376
3.6. Intra-particle diffusion study
377
The Weber–Morris equation was applied to investigate the intra-particle diffusion. The intra-particle diffusion is the sole ratelimiting step if the regression of qt against t1/2 is linear and passes through the origin [35]. However, multi-linearities can be observed in Fig. 8. The first, sharper portion was the external surface adsorption or the instantaneous adsorption. The second portion was the gradual adsorption stage where intraparticle diffusion was ratelimiting. Table 3 lists the corresponding model parameters based on the respective equation. For all initial concentrations, k1 was higher than k2 and C2 was larger than C1. This showed that the rate of Pb(II) removal was higher in the beginning because of large surface area of the adsorbent available for the adsorption of metal ions. After the adsorbed material formed a thick layer (caused by the interionic attraction and molecular association), the capacity of adsorbent got exhausted and the uptake rate was controlled by the rate at which the adsorbate was transported from the exterior to the interior sites of the adsorbent particles. None of the plots passed through the origin (Fig. 8), which revealed that the intraparticle diffusion was part of the adsorption but was not the only rate-controlling step. Some other mechanisms such as complexes or ion-exchange may also control the rate of adsorption [36,37].
378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400
solution (100 mg/L, 10 mL, pH 5) and contacting time 240 min. Two mentioned models were fitted in Fig. 9a and b for Pb(II) adsorption on the GAC. The correlation coefficients (R2) for the above models (Table 3) show that the Langmuir model fitted better than Freundlich model. Therefore, Langmuir model can be used to best describe the Pb(II) adsorption behavior on the GAC. It can be deduced that Pb(II) adsorption process is mainly homogeneous and monolayer adsorption. In addition, RL < 1.0 (Table 3) is a further indication that Langmuir adsorption is dominant. In order to compare the adsorption capacity of Pb(II) on GAC, bare GO and ACG, the maximum adsorption capacities (Qm) of various adsorbents including activated carbon, CNT and zeolite are given in Table 4. Compared to other adsorbents including bare GO and ACG synthesized here, it is obvious that GAC’s adsorption capacity is higher than those of other adsorbents.
410
4. Conclusion
425
High surface area and mesoporous graphene/activated carbon composite was synthesized from graphene oxide and glucose. The samples were characterized by X-ray diffraction pattern, Raman spectroscopy, SEM image and nitrogen adsorption–desorption isotherms. The GAC’s surface area (2012 m2/g), total pore volume (1.61 cm3/g) and ratio of mesopore to total pore volume (0.61) revealed that the GAC can be considered as a promising adsorbent for removal of different pollutants from water. To study the adsorption behavior of Pb(II) on GAC, effects of pH, GAC dosage and stirring speed were studied. The results showed that the effect of stirring speed on adsorption of Pb(II) on GAC is insignificant; however solution pH played an important role in this regard. Adsorbent dosage also influenced the adsorption of Pb(II) significantly. In addition, the adsorption performance and capacity of the GAC for removal of Pb(II) from aqueous solution were studied by measuring adsorption kinetics and isotherms. The adsorption kinetics was modeled by means of the pseudo-first order and pseudo-second order models. The GAC was found to follow the pseudo-second order model better than the pseudo-first order model. In addition, the Weber–Morris equation was applied to investigate the intra-particle diffusion. It was concluded that the intraparticle diffusion was part of the adsorption but was not the only rate-controlling step. Langmuir and Freundlich equilibrium isotherms models were used to study the adsorption of Pb(II) under the certain conditions. The correlation coefficients for the above models showed that the Langmuir model fitted better than Freundlich model. Therefore, the Pb(II) adsorption on the GAC is mainly homogeneous and monolayer adsorption. A comparison between the maximum adsorption capacity of the GAC and several other porous materials including bare ACG and GO synthesized here disclosed that the GAC has higher maximum adsorption capacity (217 mg/g) to Pb(II) than other adsorbents.
426
Uncited references [38–48].
411 412 413 414 415 416 417 418 419 420 421 422 423 424
427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457
Q4 458 459
401
3.7. Adsorption isotherms
Appendix A. Supplementary data
460
402
To optimize the use of adsorbents, adsorption isotherms are important criteria since they describe the nature of interaction between adsorbate and adsorbent. In addition, it is important to establish the most appropriate correlation for the equilibrium isotherms while optimizing the design of adsorption process to remove Pb(II) from solution. In this work, Langmuir and Freundlich equilibrium isotherms models were used to study the adsorption of Pb(II) under the conditions of adsorbent dose of 2 g/L, Pb(II)
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jece.2015.09.023.
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References
463
403 404 405 406 407 408 409
[1] H. Jabeen, K.C. Kemp, V. Chandra, Synthesis of nano zerovalent iron nanoparticles—graphene composite for the treatment of lead contaminated water, J. Environ. Manage. 130 (2013) 429–435, doi:http://dx.doi.org/10.1016/j. jenvman.2013.08.022.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
462
464 465 466
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[2] M.A.P. Cechinel, S.M.A.G. Ulson de Souza, A.A. Ulson de Souza, Study of lead(II) adsorption onto activated carbon originating from cow bone, J. Clean. Prod. 65 (2014) 342–349. [3] H.A. Aziz, M.N. Adlan, K.S. Ariffin, Heavy metals (Cd, Pb, Zn, Ni, Cu and Cr(III)) removal from water in Malaysia: post treatment by high quality limestone, Bioresour. Technol. 99 (6) (2008) 1578–1583, doi:http://dx.doi.org/10.1016/j. biortech.2007.04.007. [4] Y. Liu, J. Yan, D. Yuan, Q. Li, X. Wu, The study of lead removal from aqueous solution using an electrochemical method with a stainless steel net electrode coated with single wall carbon nanotubes, Chem. Eng. J. 218 (2013) 81–88, doi: http://dx.doi.org/10.1016/j.cej.2012.12.020. [5] Y. Huang, S. Li, J. Chen, X. Zhang, Y. Chen, Adsorption of Pb(II) on mesoporous activated carbons fabricated from water hyacinth using H3PO4 activation: adsorption capacity, kinetic and isotherm studies, Appl. Surf. Sci. (2014) , doi: http://dx.doi.org/10.1016/j.apsusc.2013.12.123. [6] S. Wang, T. Terdkiatburana, M.O. Tadé, Adsorption of Cu(II), Pb(II) and humic acid on natural zeolite tuff in single and binary systems, Sep. Purif. Technol. 62 (1) (2008) 64–70, doi:http://dx.doi.org/10.1016/j.seppur.2008.01.004. [7] A.A.H. Izzeldin, S.M. Bice, J. Catherine, O.N. Vincent, Adsorption studies of aqueous Pb(II) onto a sugarcane bagasse/multi-walled carbon nanotube composite, Phys. Chem. Earth 66 (2013) 157–166. [8] X. Deng, L. Lü, H. Li, F. Luo, The adsorption properties of Pb(II) and Cd(II) on functionalized graphene prepared by electrolysis method, J. Hazard. Mater. 183 (1–3) (2010) 923–930, doi:http://dx.doi.org/10.1016/j.jhazmat.2010.07.117. [9] G. Zhao, X. Ren, X. Gao, X. Tan, J. Li, C. Chen, Y. Huang, X. Wang, Removal of Pb(II) ions from aqueous solutions on few-layered graphene oxide nanosheets, Dalton Trans. 40 (41) (2011) 10945–10952, doi:http://dx.doi.org/10.1039/ c1dt11005e. [10] L. Cui, Y. Wang, L. Gao, L. Hu, L. Yan, Q. Wei, B. Du, EDTA functionalized magnetic graphene oxide for removal of Pb(II), Hg(II) and Cu(II) in water treatment: adsorption mechanism and separation property, Chem. Eng. J. 281 (2015) 1–10, doi:http://dx.doi.org/10.1016/j.cej.2015.06.043. [11] S. Luo, X. Xu, G. Zhou, C. Liu, Y. Tang, Y. Liu, Amino siloxane oligomer-linked graphene oxide as an efficient adsorbent for removal of Pb(II) from wastewater, J. Hazard. Mater. 274 (2014) 145–155, doi:http://dx.doi.org/10.1016/j. jhazmat.2014.03.062. [12] L. Hao, H. Song, L. Zhang, X. Wan, Y. Tang, Y. Lv, SiO2/graphene composite for highly selective adsorption of Pb(II) ion, J. Colloid Interface Sci. 369 (1) (2012) 381–387, doi:http://dx.doi.org/10.1016/j.jcis.2011.12.023. [13] G. Zhao, J. Li, X. Ren, C. Chen, X. Wang, Few-layered grapheme oxide nanosheets as superior sorbents for heavy metal ion pollution management, Environ. Sci. Technol. 45 (24) (2011) 10454–10462, doi:http://dx.doi.org/10.1021/ es203439v. [14] Z. Huang, X. Zheng, W. Lv, M. Wang, Q. Yang, F. Kang, Adsorption of lead (II) Ions from aqueous solution on low-temperature exfoliated grapheme nanosheets, Langmuir 27 (12) (2011) 7558–7562. [15] C. Zheng, X. Zhou, H. Cao, G. Wang, Z. Liu, Synthesis of porous graphene/ activated carbon composite with high packing density and large specific surface area for supercapacitor electrode material, J. Power Sources 258 (2014) 290–296, doi:http://dx.doi.org/10.1016/j.jpowsour.2014.01.056. [16] L. Jiang, J. Yan, Y. Zhou, L. Hao, R. Xue, L. Jiang, B. Yi, Activated carbon/graphene composites with high-rate performance as electrode materials for electrochemical capacitors, J. Solid State Electrochem. 17 (11) (2013) 2949–2958, doi: http://dx.doi.org/10.1007/s10008-013-2217-x. [17] W.S. Hummers, R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80 (6) (1958) 1339, doi:http://dx.doi.org/10.1021/ja01539a017. [18] C. Xu, J. Sun, L. Gao, Synthesis of novel hierarchical graphene/polypyrrole nanosheet composites and their superior electrochemical performance, J. Mater. Chem. 21 (30) (2011) 11253–11258, doi:http://dx.doi.org/10.1039/ c1jm11275a. [19] N. Saeidi, M. Parvini, M.R. Sarsabili, Studying performance of Dubinin–Astakhov and Dubinin–Raduchkevic equations to evaluate nanopore volume and pore size of MCM-41 particles, IJE Trans. A 27 (2014) 1511–1518. [20] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 40 (9) (1918) 1361–1403, doi:http://dx.doi.org/ 10.1021/ja02242a004. [21] H. Freundlich, Adsorption in solution, Phys. Chem. Soc. 40 (1906) 1361–1368. [22] T.W. Weber, R.K. Chakravorti, Pore and solid diffusion models for fixed bed adsorbers, AIChE J. 20 (2) (1974) 228–238, doi:http://dx.doi.org/10.1002/ aic.690200204. [23] M.H. Kalavathy, T. Karthikeyan, S. Rajgopal, L.R. Miranda, Kinetic and isotherm studies of Cu(II) adsorption onto H3PO4-activated rubber wood sawdust, J. Colloid Interface Sci. 292 (2) (2005) 354–362, doi:http://dx.doi.org/10.1016/j. jcis.2005.05.087. [24] W.J. Weber, J.R. Moris, Kinetics of adsorption on carbon from solution, J. San. Eng. Div. ASCE Civil Eng. 89 (1963) 31–39. [25] O.C. Compton, S.T. Nguyen, Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials, Small 6 (6) (2010) 711–723, doi:http://dx.doi.org/10.1002/smll.200901934. [26] Y. Chen, X. Zhang, H. Zhang, X. Sun, D. Zhang, Y. Ma, High-performance supercapacitors based on a graphene-activated carbon composite prepared by chemical activation, RSC Adv. 2 (20) (2012) 7747–7753, doi:http://dx.doi.org/ 10.1039/c2ra20667f. [27] M.K. Aroua, S.P.P. Leong, L.Y. Teo, C.Y. Yin, W.M.A.W. Daud, Real-time determination of kinetics of adsorption of lead(II) onto palm shell-based activated
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
9
carbon using ion selective electrode, Bioresour. Technol. 99 (13) (2008) 5786– 5792. P.L. Homagai, K.N. Ghimire, K. Inoue, Adsorption behavior of heavy metals onto chemically modified sugarcane bagasse, Bioresour. Technol. 101 (6) (2010) 2067–2069, doi:http://dx.doi.org/10.1016/j.biortech.2009.11.073. D. Xu, X. Tan, C. Chen, X. Wang, Removal of Pb(II) from aqueous solution by oxidized multiwalled carbon nanotubes, J. Hazard. Mater. 154 (1–3) (2008) 407–416, doi:http://dx.doi.org/10.1016/j.jhazmat.2007.10.059. G.P. Rao, C. Lu, F. Su, Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review, Sep. Purif. Technol. 58 (1) (2007) 224–231, doi: http://dx.doi.org/10.1016/j.seppur.2006.12.006. A.E. Ofomaja, E.I. Unuabonah, N.A. Oladoja, Competitive modeling for the biosorptive removal of copper and lead ions from aqueous solution by Mansonia wood sawdust, Bioresour. Technol. 101 (11) (2010) 3844–3852, doi: http://dx.doi.org/10.1016/j.biortech.2009.10.064. H. Lu, W. Zhang, Y. Yang, X. Huang, S. Wang, R. Qiu, Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar, Water Res. 46 (3) (2012) 854–862, doi:http://dx.doi.org/10.1016/j.watres.2011.11.058. F. Di Natale, A. Erto, A. Lancia, D. Musmarra, Mercury adsorption on granular activated carbon in aqueous solutions containing nitrates and chlorides, J. Hazard. Mater. 192 (3) (2011) 1842–1850, doi:http://dx.doi.org/10.1016/j. jhazmat.2011.07.021. E.N. El Qada, S.J. Allen, G.M. Walker, Adsorption of methylene blue onto activated carbon produced from steam activated bituminous coal: a study of equilibrium adsorption isotherm, Chem. Eng. J. 124 (1–3) (2006) 103–110, doi: http://dx.doi.org/10.1016/j.cej.2006.08.015. A. Mittal, A. Malviya, D. Kaur, J. Mittal, L. Kurup, Studies on the adsorption kinetics and isotherms for the removal and recovery of methyl orange from wastewaters using waste materials, J. Hazard. Mater. 148 (1–2) (2007) 229– 240, doi:http://dx.doi.org/10.1016/j.jhazmat.2007.02.028. F.C. Wu, R.L. Tseng, R.S. Juang, Comparisons of porous and adsorption properties of carbons activated by steam and KOH, J. Colloid Interface Sci. 283 (1) (2005) 49–56, doi:http://dx.doi.org/10.1016/j.jcis.2004.08.037. W.H. Cheung, Y.S. Szeto, G. McKay, Intraparticle diffusion processes during acid dye adsorption onto chitosan, Bioresour. Technol. 98 (15) (2007) 2897–2904, doi:http://dx.doi.org/10.1016/j.biortech.2006.09.045. D. Angin, Production and characterization of activated carbon from sour cherry stones by zinc chloride, Fuel 115 (2014) 804–811, doi:http://dx.doi.org/ 10.1016/j.fuel.2013.04.060. X. Ma, F. Zhang, J. Zhu, L. Yu, X. Liu, Preparation of highly developed mesoporous activated carbon fiber from liquefied wood using wood charcoal as additive and its adsorption of methylene blue from solution, Bioresour. Technol. 164 (2014) 1–6, doi:http://dx.doi.org/10.1016/j.biortech.2014.04.050. T.H. Liou, Development of mesoporous structure and high adsorption capacity of biomass-based activated carbon by phosphoric acid and zinc chloride activation, Chem. Eng. J. 158 (2) (2010) 129–142, doi:http://dx.doi.org/10.1016/j. cej.2009.12.016. R.L. Tseng, S.K. Tseng, Pore structure and adsorption performance of the KOHactivated carbons prepared from corncob, J. Colloid Interface Sci. 287 (2) (2005) 428–437, doi:http://dx.doi.org/10.1016/j.jcis.2005.02.033. M. Olivares-Marín, C. Fernández-González, A. Macías-García, V. Gómez-Serrano, Preparation of activated carbon from cherry stones by chemical activation with ZnCl2, Appl. Surf. Sci. 252 (17) (2006) 5967–5971, doi:http://dx.doi. org/10.1016/j.apsusc.2005.11.008. S. Yorgun, N. Vural, H. Demiral, Preparation of high-surface area activated carbons from Paulownia wood by ZnCl2 activation, Micropor. Mesopor. Mater. 122 (1–3) (2009) 189–194, doi:http://dx.doi.org/10.1016/j.micromeso.2009.02.032. J. Srenscek-Nazzal, W. Kaminska, B. Michalkiewicz, Z.C. Koren, Production, characterization and methane storage potential of KOH-activated carbon from sugarcane molasses, Ind. Crops Prod. 47 (2013) 153–159, doi:http://dx.doi.org/ 10.1016/j.indcrop.2013.03.004. A. Minoda, S. Oshima, H. Iki, E. Akiba, Synthesis of KOH-activated porous carbon materials and study of hydrogen adsorption, J. Alloys Compd. 580 (2013) S301–S304, doi:http://dx.doi.org/10.1016/j.jallcom.2013.02.085. E. Raymundo-Piñero, P. Azaïs, T. Cacciaguerra, D. Cazorla-Amorós, A. LinaresSolano, F. Béguin, KOH and NaOH activation mechanisms of multiwalled carbon nanotubes with different structural organization, Carbon 43 (4) (2005) 786–795, doi:http://dx.doi.org/10.1016/j.carbon.2004.11.005. N. Ferrera-Lorenzo, E. Fuente, I. Suárez-Ruiz, Ruiz, B., KOH activated carbon from conventional and microwave heating system of a macroalgae waste from the agar–agar industry, Fuel Process. Technol. 121 (2014) 25–31. T. Mitome, Y. Uchida, Y. Egashira, K. Hayashi, A. Nishiura, N. Nishiyama, Adsorption of indole on KOH-activated mesoporous carbon, Colloids Surf. A Physicochem. Eng. Aspects 424 (2013) 89–95, doi:http://dx.doi.org/10.1016/j. colsurfa.2013.02.022. E. Kusvuran, D. Yildirim, A. Samil, O. Gulnaz, A study: removal of Cu(II), Cd(II), and Pb(II) ions from real industrial water and contaminated water using activated sludge biomass, Clean 40 (11) (2012) 1273–1283, doi:http://dx.doi. org/10.1002/clen.201100443. H.C. Tao, H.R. Zhang, J.B. Li, W.Y. Ding, Biomass based activated carbon obtained from sludge and sugarcane bagasse for removing lead ion from wastewater, Bioresour. Technol. 192 (2015) 611–617, doi:http://dx.doi.org/10.1016/j.biortech.2015.06.006.
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[51] M. Imamoglu, O. Tekir, Removal of copper (II) and lead (II) ions from aqueous solutions by adsorption on activated carbon from a new precursor hazelnut husks, Desalination 228 (1–3) (2008) 108–113. [52] Y. Kikuchi, Q. Qian, M. Machida, H. Tatsumoto, Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution, Carbon 44 (2) (2006) 195–202, doi:http://dx.doi.org/10.1016/j.carbon.2005.07.040. [53] P. Brown, I.A. Atly Jefcoat, D. Parrish, S. Gill, E. Graham, Evaluation of the adsorptive capacity of peanut hull pellets for heavy metals in solution, Adv. Environ. Res. 4 (1) (2000) 19–29, doi:http://dx.doi.org/10.1016/S1093-0191 (00)00004-6. [54] G. Issabayeva, M.K. Aroua, N.M.N. Sulaiman, Removal of lead from aqueous solutions on palm shell activated carbon, Bioresour. Technol. 97 (18) (2006) 2350–2355, doi:http://dx.doi.org/10.1016/j.biortech.2005.10.023. [55] R.R. Bansode, J.N. Losso, W.E. Marshall, R.M. Rao, R.J. Portier, Adsorption of metal ions by pecan shell-based granular activated carbons, Bioresour. Technol. 89 (2) (2003) 115–119, doi:http://dx.doi.org/10.1016/S0960-8524(03) 00064-6. [56] V.J.P. Vilar, C.M.S. Botelho, R.A.R. Boaventura, Boaventura, Influence of pH, ionic strength and temperature on lead biosorption by Gelidium and agar extraction algal waste, Proc. Biochem. 40 (10) (2005) 3267–3275, doi:http://dx.doi.org/ 10.1016/j.procbio.2005.03.023.
[57] M. Abdulkarim, F.A. Al-Rub, Adsorption of lead ions from aqueous solution onto activated carbon and chemically-modified activated carbon prepared from date pits, Adsorp. Sci. Technol. 22 (2004) 119–134. [58] M.M. Johns, W.E. Marshall, C.A. Toles, Agricultural by-products as granular activated carbons for adsorbing dissolved metals and organics, J. Chem. Technol. Biotechnol. 71 (2) (1998) 131–140, doi:http://dx.doi.org/10.1002/ (SICI)1097-4660(199802)71:2<131::AID-JCTB821>3.0.CO;2-K. [59] L. Wang, J. Zhang, R. Zhao, Y. Li, C. Li, C. Zhang, Adsorption of Pb(II) on activated carbon prepared from Polygonum orientale Linn.: kinetics, isotherms, pH, and ionic strength studies, Bioresour. Technol. 101 (15) (2010) 5808–5814, doi: http://dx.doi.org/10.1016/j.biortech.2010.02.099. [60] N.A. Kabbashi, M.A. Atieh, A. Al-Mamun, M.E. Mirghami, M.D.Z. Alam, N. Yahya, Kinetic adsorption of application of carbon nanotubes for Pb(II) removal from aqueous solution, J. Environ. Sci. 21 (4) (2009) 539–544, doi:http://dx.doi.org/ 10.1016/S1001-0742(08)62305-0. [61] Y.H. Li, J. Ding, Z. Luan, Z. Di, Y. Zhu, C. Xu, D. Wu, B. Wei, Competitive adsorption of Pb2+, Cu2+ and Cd2+ ions from aqueous solutions by multiwalled carbon nanotubes, Carbon 41 (14) (2003) 2787–2792, doi:http://dx.doi.org/ 10.1016/S0008-6223(03)00392-0. [62] H.J. Wang, A.L. Zhou, F. Peng, H. Yu, L.F. Chen, Adsorption characteristic of acidified carbon nanotubes for heavy metal Pb(II) in aqueous solution, Mater. Sci. Eng. A 466 (1–2) (2007) 201–206, doi:http://dx.doi.org/10.1016/j. msea.2007.02.097.
Please cite this article in press as: N. Saeidi, et al., High surface area and mesoporous graphene/activated carbon composite for adsorption of Pb (II) from wastewater, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.09.023
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