Chemosphere 130 (2015) 59–65

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Lead and copper removal from aqueous solutions using carbon foam derived from phenol resin Chang-Gu Lee a, Jun-Woo Jeon a, Min-Jin Hwang a, Kyu-Hong Ahn a, Chanhyuk Park a, Jae-Woo Choi a,b,⇑, Sang-Hyup Lee a,c,⇑ a b c

Center for Water Resource Cycle Research, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea Department of Energy and Environmental Engineering, University of Science and Technology (UST), Daejeon 305-350, Republic of Korea Green School, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 136-701, Republic of Korea

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Phenolic resin-based carbon foam is a

low-cost adsorbent alternative.  Lead and copper removal from

aqueous solution is possible with carbon foam.  Key mechanism of lead and copper removal on carbon foam is surface precipitation.  Maximum sorption capacities were 460.50 mg g1 for lead and 212.14 mg g1 for copper.

a r t i c l e

i n f o

Article history: Received 2 October 2014 Received in revised form 23 February 2015 Accepted 23 February 2015

Handling Editor: Min Jang Keywords: Carbon foam Lead removal Copper removal Batch experiments Surface precipitation

a b s t r a c t Phenolic resin-based carbon foam was prepared as an adsorbent for removing heavy metals from aqueous solutions. The surface of the produced carbon foam had a well-developed open cell structure and the specific surface area according to the BET model was 458.59 m2 g1. Batch experiments showed that removal ratio increased in the order of copper (19.83%), zinc (34.35%), cadmium (59.82%), and lead (73.99%) in mixed solutions with the same initial concentration (50 mg L1). The results indicated that the Sips isotherm model was the most suitable for describing the experimental data of lead and copper. The maximum adsorption capacity of lead and copper determined to Sips model were 491 mg g1 and 247 mg g1. The obtained pore diffusion coefficients for lead and copper were found to be 1.02  106 and 2.42  107 m2 s1, respectively. Post-sorption characteristics indicated that surface precipitation was the primary mechanism of lead and copper removal by the carbon foam, while the functional groups on the surface of the foam did not affect metal adsorption. Ó 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding authors at: Center for Water Resource Cycle Research, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136791, Republic of Korea. Tel.: +82 2 958 5820; fax: +82 2 958 5839 (J.W. Choi). Tel.: +82 2 958 6945; fax: +82 2 958 5839 (S.H. Lee). E-mail addresses: [email protected] (J.-W. Choi), [email protected] (S.-H. Lee). http://dx.doi.org/10.1016/j.chemosphere.2015.02.055 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Carbon foam is a sponge-like carbon material with high strength, light weight, high thermal/electrical management, and a large surface area with open cell structure (Chen et al., 2006a; Tondi et al., 2009). Because of these inherent properties, carbon

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foam is used as catalyst support, filter for molten metal and corrosive chemicals, porous electrodes, and impact/energy/acoustic absorbers (Grujicic et al., 2006; Kim and Cunningham, 2010; An et al., 2011; Kang et al., 2011; Chun et al., 2012; Emmel and Aneziris, 2012; Shao et al., 2013; Amaral-Labat et al., 2013). Carbon foam is also applied as a biological filter in water treatment systems and as an adsorbent in gas- or liquid-phase environments (Chen et al., 2006b; Bao et al., 2011; Liu et al., 2013; Burke et al., 2013). Initially, carbon foam was produced as a refractory thermal insulating material in 1964 by Ford (1964). Over the following decades, various types of carbon foam were produced depending on the precursors and manufacturing processes. They are classified as graphitic and non-graphitic carbon foam. Graphitic foam was derived from graphitization of coal, pitched at a temperature of at least 2600 °C (Song et al., 2012; Focke et al., 2014). They have very good thermal and electrical conductivity as a result of the high degree of graphitization. Non-graphitic foam was prepared by carbonization of organic polymers such as phenol formaldehyde and sucrose (Prabhakaran et al., 2007; Lei et al., 2010). They have low thermal conductivity and can be used as thermal insulation material. In addition, non-graphitic foam has potential applications as low-cost carbon foam due to the low-cost of manufacture. Lowcost adsorbent requires a simple manufacturing process, as well as a large amount of precursor that can be easily obtained. Recently, much research has been carried out to produce low-cost carbon foam though the use of commercially available phenolic resin (Manocha et al., 2010; Wu et al., 2011). The price of phenolic resin is less than US $ 1 kg1. Carbonaceous adsorbents are known as one of the most effective methods for heavy metal wastewater treatment. A large number of studies were carried out on the removal of heavy metals in water using activated carbon or modified activated carbon (Zhu et al., 2009; Fu and Wang, 2011). Activated carbon is the most commonly used adsorbent, but it is relatively expensive. The price of activated carbon vary depending on the quality, it is about US $ 9 kg1 (Kurniawan et al., 2006). In recent years, many studies have been conducted on the development of heavy metal adsorbents using low-cost material, such as agricultural by-product or biomass (Ahmaruzzaman and Gupta, 2011; Inyang et al., 2012). Carbon foam has rarely been used for heavy metal adsorption, despite its affordability (about US $ 3 kg1) (Tondi et al., 2010a). Burke et al. (2013) conducted the only know study using carbon foam chemical oxidation for lead ion removal from aqueous solution. In the current study, a phenolic resin-based carbon foam was prepared as a low-cost adsorbent for lead and copper ion removal from aqueous solution. The chemical composition and surface characteristics of the prepared adsorbent were analyzed. Batch adsorption experiments were conducted to evaluate the removal capacity of heavy metals. The removal mechanisms of copper and lead were also analyzed.

2. Materials and methods 2.1. Preparation of carbon foam Phenolic resin-based carbon foam was supplied from SmithersOasis Korea Co. Ltd. Firstly, the procedure involved the addition of 1.0 kg of phenol to a four-necked reactor, 1.5 kg of formaldehyde was then poured into the reactor with slow stirring followed by 40 g of a base catalyst, and the contents were stirred for a further 2 h at 75 °C. The mixture was cooled to 35 °C and neutralized to pH 6–7 using dilute sulfuric acid. The moisture content was then adjusted to 9% through dehydration under vacuum with reduced pressure. Secondly, 2 g of alkyl ether type surfactant was mixed

with the prepared phenolic resin and the mixture was stirred thoroughly in a cylindrical mold at a low stirring speed. Thirdly, 80 g of organic acid curing agent and 20 g of hydrocarbon foaming agent were added to the mixture and the stirring rate was increased to 1000 rpm. The synthesized foam was aged in a convection oven at 60 °C. Finally, the dried foam was put into an electric furnace and the air was removed using a vacuum pump. The sample was carbonized at a heating rate of 5 °C min1 under a nitrogen stream of 100 mL min1 up to 900 °C, held at the final temperature for 2 h, and then slowly cooled in the nitrogen atmosphere. 2.2. Characterization of carbon foam The chemical composition of the carbon foam was determined using an X-ray fluorescence spectrometer (XRF, ZSX Primus II, Rigaku, Japan). The surface morphology of the sample was investigated using a scanning electron microscope (SEM, Inspect F50, FEI, USA) at 10.00 kV. Nitrogen gas (N2) adsorption–desorption experiments were performed using a surface area analyzer (nanoPOROSITY-XQ, Mirae Scientific Instruments, Korea) after pretreatment of the sample at 200 °C. The surface area, mesopore volume, and micropore volume were calculated from the N2 isotherm according to the methods of Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), and Horvath–Kawazoe (HK). The potentiometric titration method of Parks and Bruyn (1962) was used to determine the point of zero charge (pHPZC). One gram of carbon foam was added to 250 mL beakers with 100 mL of electrolyte solution (0.1, 0.01, and 0.001 M NaCl). The solution was stirred for 2 h and then the pH was measured after each increment of 0.1 M HCl or 0.1 M NaOH. The results of the titration were plotted and the pHPZC was determined using a graphical method. The crystalline structure of the sample was measured by an X-ray diffractometer (XRD, D-max 2500/PC, Rigaku, Japan) with Cu Ka radiation and a fixed power source (40 kV and 200 mA). The diffraction data were collected over a 2h range between 20° and 80°, at a scanning rate of 0.5° min1. Fourier transform infrared spectroscopy (FTIR, Infinity Gold, Thermo Mattson, USA) was used to analyze the change in surface functional groups on the carbon foam before and after the sorption experiments. 2.3. Batch adsorption experiments An initial evaluation of the sorption ability of carbon foam was performed using a mixed heavy metal solution containing lead, cadmium, zinc, and copper. The concentration of each metal was adjusted to 50 mg L1 through dilution using standard solution purchased from Kanto Chemical Inc. Approximately 0.03 g of sorbent was added to a 250 mL Erlenmeyer flask with 200 mL of the heavy metal solution at room temperature. After shaking in a rotary shaker for 24 h, the solution was sampled using a 0.45 lm syringe filter. The concentration of each metal in the sampled solution was analyzed using an inductively coupled plasma-optical emission spectrometer (ICP-OES, Prodigy ICP, Teledyne Leeman Labs, USA). Additional batch experiments were carried out to analyze the sorption properties of lead and copper. The desired concentration of lead and copper were prepared by diluting the stock solutions (1000 mg L1), which were made from lead nitrate (Pb(NO3)2, Sigma–Aldrich, USA) and copper chloride dihydrate (CuCl22H2O, Sigma–Aldrich, USA). The solution pH was adjusted close to neutral in consideration of the solubility of each metal. The solubility of lead and copper calculated from Visual MINTEQ 3.0 was shown in Fig. S2. The solution pH of lead and copper were adjusted 7 and 5, respectively. Kinetic batch tests were performed in 250 mL Erlenmeyer flasks containing 0.03 g of carbon foam with 200 mL of the diluted solution. Sorption experiments were performed

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using 50 mg L1 of lead or copper solutions for up to 40 h. At specific time intervals, the solution was sampled using a 0.45 lm syringe filter and the residual concentration of metal was analyzed using an ICP-AES. Equilibrium sorption isotherms were determined using a solution containing between 5 and 400 mg L1 of lead or copper. In this step, batch tests were performed in 50 mL conical tubes containing 0.03 g of carbon foam and 50 mL of the diluted solution. After shaking, both the solution and sorbent were collected for further analysis. All the batch experiments were performed in duplicates. 2.4. Regeneration test The reusability of the adsorbent was evaluated by regeneration of the copper-adsorbed carbon foam. Sorption experiments were performed using 1.0 g of adsorbents with 50 mL of the solution containing 50 mg L1 of copper. Prior to reuse, the regeneration tests were conducted using chemical and electrical methods. For the chemical regeneration, copper-adsorbed carbon foam was placed in 200 mL of a 0.1 N HNO3 solution and gently stirred for 1 h. The electrical regeneration was conducted using a DC power supply (RDP-305, SMART, Korea) at 10 V for 20 min in 200 mL of 0.1 N NaCl solution. The reuse tests were performed after the removal of surface water. 3. Results and discussion

Fig. 1. Scanning electron microscope image of the carbon foam.

Table 2 Physicochemical properties of carbon foam. Bulk density BET surface (g cm3) area (m2 g1)

BJH mesopore volume (cm3 g1)

HK micropore volume (cm3 g1)

pHPZC (–)

0.40

0.098

0.17

11.38

458.59

Note: pHPZC means point of zero charge.

3.1. Characterization of carbon foam The chemical composition from the XRF analysis (Table 1) indicated that the synthesized carbon foam was mainly composed of C (90.40%). This outcome is in agreement with the results of the carbon yield of the phenolic resin (Manocha et al., 2010). Elemental analysis showed that the carbon foam had various amounts of inorganic elements and a relatively high amount of S (3.50%) and Ca (4.86%). These inorganic elements were derived from residues included in the foaming process such as methyl sulfate (CH4O4S) and calcium hydroxide (Ca(OH)2). The type of sulfur and calcium component was described with the results of the XRD analysis in Section 3.4. The surface morphology of the prepared carbon foam determined using the scanning electron microscope (SEM) is shown in Fig. 1. The SEM image shows that the pores of different sizes with open cell structures had developed on the surface of the carbon foam. The analysis of the image revealed that the pore sizes varied from approximately 25 to 150 lm. The bulk density of the carbon foam used in this study was 0.40 g cm3. The nitrogen adsorption–desorption test was conducted to determine the specific surface area and pore size distribution of the prepared sample (Table 2). The N2 sorption isotherms of the carbon foam can be described as Type-I isotherms (Fig. S3), which are typical for microporous materials (Chen et al., 2007; Tondi et al., 2010b). BET fitting was carried out at a relative pressure range of 0.005–0.08 for the positive BET constant. The specific surface area of the carbon foam, according to BET model, was 458.59 m2 g1. BJH analysis indicated that the mesopore volume of carbon foam was 0.098 cm3 g1 and HK analysis founded that the micropore volume of sample was 0.17 cm3 g1. Similar results

Table 1 Chemical composition of carbon foam. C (%)

Na (%)

Mg (%)

Si (%)

P (%)

S (%)

Cl (%)

K (%)

Ca (%)

Sr (%)

90.40

0.14

0.026

0.017

0.036

3.50

0.013

0.98

4.86

0.026

Fig. 2. Removal of heavy metals (Cu, Zn, Cd, and Pb) by carbon foam in mixed solutions (adsorbent dosage = 0.15 g L1, initial concentration of each metal = 50 mg L1, reaction time = 24 h, solution pH = not adjusted).

were observed in chemically activated carbon foam by KOH (Liu et al., 2013). The activated carbon foam (AF-500) has a specific surface area of 554 m2 g1, a mesopore volume of 0.098 cm3 g1, and a micropore volume of 0.22 cm3 g1. The point of zero charge of prepared carbon foam was also investigated using the potentiometric titration method. Net surface charge in the pH-charge graph was zero at about pH 11.38 (graph not shown). 3.2. Sorption of heavy metals Removal ratio of each heavy metal in mixed solution by the prepared carbon foam is shown in Fig. 2. Removal efficiency increased in the order of copper (19.83%), zinc (34.35%), cadmium (59.82%), and lead (73.99%), given the same initial concentration (50 mg L1). The higher removal efficiency of lead can be explained through the higher atomic weight and electronegativity (Jiang et al., 2006; Shi et al., 2009). The electronegativity of the metals

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is in the order of lead (2.33), copper (1.90), cadmium (1.69), and zinc (1.65). The adsorbent types or surface characteristics also had a significant effect on heavy metal removal. According to Kazemipour et al. (2008), the removal efficiency of walnut shell based carbon followed the order of copper, lead, zinc, and cadmium while hazelnut shell based carbon followed the order of lead, copper, cadmium, and zinc. In contrast, multi-walled carbon nanotube has affinity in the following order copper, zinc, lead, and cadmium (Salam et al., 2012). As described in the following sections, more detailed analysis of lead and copper was performed to clarify the removal mechanism by carbon foam. 3.3. Sorption model analysis To determine adsorption properties, the adsorption isotherms for the prepared adsorbent were studied for various lead and copper concentrations. Adsorption isotherms are the most important information for analyzing and designing an adsorption process. In this study, the adsorption amounts are predicted with three types of adsorption isotherms given as follows (Freundlich, 1907; Langmuir, 1918; Sips, 1948):

Q¼

Q max bC 1 þ bC

ð1Þ

Q ¼ KC 1=n Q¼

ð2Þ

Q max bC 1 þ bC

ep

1=n

1=n

the adsorption capacity (L g1), 1/n is the Freundlich and Sips constant related to the adsorption intensity (heterogeneity factor). The lead and copper adsorption equilibrium isotherms on the adsorbents were examined and the results are shown in Fig. 3(a) and (b). The isotherm parameters were obtained and summarized in Table S1. According to squared correlation coefficient (R2) value for isotherm models, the Sips isotherm model provided best predict with the all experimental data that other isotherm models. The applicability of the Sips isotherm suggests that the adsorbent surfaces are energetically heterogeneous for lead and copper molecules (Sips, 1948), probably indicates multilayer adsorption. The maximum adsorption capacity of lead and copper determined to Sips model were 491 mg g1 and 247 mg g1, respectively. In order to determine the adsorption kinetic performance, the mathematical model for simulation of the batch adsorption system is required to estimate the mass transient behavior. The pore diffusion adsorption model employed in this study is constructed on the basis of the following assumptions. The driving force for intraparticle mass transfer is adsorbate concentration gradient in the particle phase. The adsorbents are spherical with uniform radius, density, and porosity (Ponnusami et al., 2010). The local equilibrium between bulk and particle phases is established within the pores. The governing intraparticle continuity equation for the mass transfer model is described as:

ð3Þ

where C is the equilibrium concentration of the metal in aqueous solution (mg L1), Qmax is the maximum adsorption capacity (mg g1), b is the Langmuir constant connected to the affinity of the binding sites (L mg1), K is the Freundlich constant related to

  @C p @q 1 @ @Cp r 2 Dp þ qp ¼ ep 2 @t r @r @t @r

ð4Þ

where ep is the particle porosity, qp is particle density of the adsorbent (g L1), rp is radial coordinate of the particle (m), Dp is internal pore diffusivity (m2 s1), Cp is solution concentration in pore (mg L1), and t is time (s), q is particle phase adsorbate concentration (mg g1). The q also can be calculated from solution concentration in

Fig. 3. Adsorption equilibrium isotherm of (a) lead and (b) copper (adsorbent dosage = 0.6 g L1, initial concentration = 5–400 mg L1, reaction time = 24 h, solution pH = 7 for lead and 5 for copper). Adsorption kinetic data of (c) lead and (d) copper (adsorbent dosage = 0.15 g L1, initial concentration = 50 mg L1, reaction time = 40 h, solution pH = 7 for lead and 5 for copper).

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63

pore by adsorption equilibrium isotherm parameters mentioned earlier. In the pore diffusion model, Langmuir, Freundlich, and Sips isotherms were incorporated to describe the partition behavior of each molecule. The initial and boundary conditions are:

t ¼ 0; C p ¼ 0 r ¼ 0;

@C p ¼0 @r

r ¼ rp ;

ep Dp

@C p ¼ kf ðC b  C s Þ @r

ð5Þ ð6Þ

ð7Þ

where kf is the external-film transfer coefficient (m s1), rp is the radius of adsorbent particle (m), and Cb and Cs are the concentration in bulk aqueous phase and external surface (mg L1), respectively. Also the mass transfer of adsorbate from the bulk phase to the particle phase is expressed by:

dC b M dq 3kf M ¼  ðC b  C s Þ V dt rp qp V dt

ð8Þ

where M is mass of adsorbent (g) and V is system volume (L). The numerical method employed for solving the governing equations by orthogonal collocation and Nelder–Mead method (Lee et al., 2004). In this study, a MATLAB computer program was specifically developed to evaluate kf and Dp by the best predicting of the experimental data to the mathematical simulated result based on the maximization of the R2 value. Overall adsorption kinetic data for lead and copper on the adsorbent are shown in Fig. 3(c) and (d). Furthermore, results of the diffusion model application presented in terms of the concentration decay curves. About 10 h and 30 h were needed to reach equilibrium for lead and copper, respectively. The adsorption rate of lead and copper were in agreement with their hydrated radius. It is expected that the molecules with smaller hydrated radius will show a more rapidly adsorbed on the carbon form due to easily diffuse toward the adsorption site. The hydrated radius of lead and copper is 4.01 Å and 4.30 Å, respectively (Mimura et al., 2002). As illustrated in Fig. 3(c) and (d), the experimental data is well described by the diffusion model incorporated with Sips isotherm. The obtained pore diffusion coefficients for lead and copper were found to be 1.02  106 and 2.42  107 m2 s1, respectively. It should be noted that this values are about one order of magnitude higher than that on calcium alginate beads and granular activated carbons (Sergios et al., 2006; Abbas et al., 2009). The estimated values of kinetic parameters from different adsorption isotherm equations are listed in Table S2. 3.4. Post-sorption characteristics XRD patterns of the carbon foam, before and after heavy metal adsorption, are shown in Fig. 4. The calcium and sulfur component described above was found to exist in the form of calcium sulfide (CaS, oldhamite, PDF 04-005-5935) in the carbon foam. This calcium sulfide is used in the treatment of metal-containing wastewater through the following reactions (Mihara et al., 2008):

CaS $ Ca2þ þ S2

ð9Þ

Me2þ þ S2 $ MeS

ð10Þ

2CaS þ 2H2 O $ CaðHSÞ2 þ CaðOHÞ2

ð11Þ

CaðHSÞ2 $ Ca2þ þ 2HS

ð12Þ

Me2þ þ HS $ MeS þ Hþ

ð13Þ

where Me is a metal contained in the wastewater, corresponding to lead and copper in this study. The results of these reactions were

Fig. 4. XRD patterns of carbon foam before and after adsorption with lead and copper (O: oldhamite (CaS); G: galena (PbS); V: vaterite (CaCO3); C: covellite (CuS)) (adsorbent dosage = 0.6 g L1, initial concentration = 50 mg L1, reaction time = 24 h, solution pH = 7).

Fig. 5. FTIR patterns of carbon foam before and after adsorption with lead and copper (adsorbent dosage = 0.6 g L1, initial concentration = 50 mg L1, reaction time = 24 h, solution pH = 7).

confirmed from the XRD peaks after adsorption. Lead sulfide (PbS, galena, PDF 04-004-4329) peaks were identified after adsorption of lead; calcium carbonate (CaCO3, vaterite, PDF 04-011-5958) peaks were also observed. Peaks of copper sulfide (CuS, covellite, PDF 04006-9635) were observed in the XRD patterns after copper adsorption. These results indicated that the surface precipitation was the primary mechanism of lead and copper removal on carbon foam (Lewis, 2010). The surface functional groups of the carbon foam were analyzed using FTIR spectroscopy (Fig. 5). The intense bands at 1435.16 and 875.24 cm1 were assigned to the asymmetric stretch (m3) and in-plane bend (m4) of carbonate in amorphous calcium carbonate, respectively (Al-Hosney and Grassian, 2005). However, FTIR spectra did not change before and after adsorption. These results denote that the functional groups on the surface of the carbon foam did not affect the metal adsorption (Inyang et al., 2012).

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3.5. Regeneration of carbon foam Experiments were carried out using a commonly utilized chemical and electrical regeneration method used for electrically conducting carbonaceous adsorbents (Salvador et al., 2015). The outcome of the regeneration tests are shown in Fig. S1. In the chemical regeneration trials, the removal ratio increased in the first reuse test and then decreased gradually with each subsequent reuse. According to Zhang (2011), the increase of removal efficiency at the second number of use may be due to the release of remaining cations, such as calcium and sodium, during the first desorption process. The reductions were largely due to the structural deterioration of the adsorbents because of the continuous regeneration (Vijayaraghavan et al., 2005). Debris generated in desorption process was not used for the next adsorption cycle. But, weight loss due to the debris was not remarkable. The removal efficiency of the chemical regeneration was over 75% for five cycles. The regeneration efficiency of the electrical method reduced more rapidly than the chemical method. After five usages, the removal efficiency decreased to 11.77%. These results are associated with the continuous accumulation of copper on the negative electrode plate by chemical regeneration (Xing et al., 2007). Also, the amount of debris generated in chemical desorption process was higher than chemical desorption. However, the findings show the promising possibility of the chemical regeneration of the carbon foam. 4. Conclusions In this study, phenolic resin-based carbon foam was prepared as a low-cost adsorbent. The prepared carbon foam had a large surface area with well-developed micropores. The results demonstrate that the carbon foam was effective for the removal of heavy metals with maximum sorption capacities of 491.36 mg g1 for lead and 246.66 mg g1 for copper. It was revealed that the removal of lead and copper by carbon foam was due to surface precipitation. The functional groups did not appear to have a role in the process. This study demonstrates that carbon foam is an excellent adsorbent for the removal of heavy metals from water. Acknowledgement This research is supported by Korea Ministry of Environment as ‘‘The Conversing Technology Program’’ (2012000600001). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2015.02.055. References Abbas, H.S., Balasim, A.A., Jenan, A.A.B., 2009. Removal of lead, copper, chromium, and cobalt ions onto granular activated carbon in batch and fixed-bed adsorbers. Chem. Eng. J. 155, 647–653. Ahmaruzzaman, M., Gupta, V.K., 2011. Rice husk and its ash as low-cost adsorbents in water and wastewater treatment. Ind. Eng. Chem. Res. 50, 13589–13613.K. Al-Hosney, H.A., Grassian, V.H., 2005. Water, sulfur dioxide and nitric acid adsorption on calcium carbonate: a transmission and ATR-FTIR study. Phys. Chem. Chem. Phys. 7, 1266–1276. Amaral-Labat, G., Gourdon, E., Fierro, V., Pizzi, A., Celzard, A., 2013. Acoustic properties of cellular vitreous carbon foams. Carbon 58, 76–86. An, S., Park, J.H., Shin, C.H., Joo, J., Ramasamy, E., Hwang, J., Lee, J., 2011. Welldispersed Pd3Pt1 alloy nanoparticles in large pore sized mesocellular carbon foam for improved methanol-tolerant oxygen reduction reaction. Carbon 49, 1108–1117. Bao, Y., Zhan, L., Wang, C., Wang, Y., Qiao, W., Ling, L., 2011. Carbon foams used as packing media in a biological aerated filter system. Mater. Lett. 65, 3154–3156.

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