Chemosphere 136 (2015) 20–26

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Adsorption characteristics of diclofenac and sulfamethoxazole to graphene oxide in aqueous solution Seung-Woo Nam a,b, Chanil Jung b, Hang Li c, Miao Yu c, Joseph R.V. Flora b, Linkel K. Boateng b, Namguk Her d, Kyung-Duk Zoh a,⇑, Yeomin Yoon b,⇑ a

Department of Environmental Health, Graduate School of Public Health, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 157-742, South Korea Department of Civil and Environmental Engineering, University of South Carolina, Columbia, 300 Main Street, Columbia, SC 29208, USA Department of Chemical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA d Department of Civil and Environmental Engineering, Korea Army Academy at Young-Cheon, 135-1 Changhari, Kokyungmeon, Young-Cheon, Gyeongbuk 770-849, South Korea b c

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

 GO adsorptive properties were

characterized by AFM, XRD, XPS, ZP, and DLS.  The sonication of GO significantly improved the removal of target compounds.  The main binding mechanisms were hydrophobic and p–p EDA interactions.

a r t i c l e

i n f o

Article history: Received 17 December 2014 Received in revised form 2 March 2015 Accepted 29 March 2015

Handling Editor: Min Jang Keywords: Diclofenac Sulfamethoxazole Graphene oxide Adsorption Sonication Molecular modeling

a b s t r a c t The adsorptive properties of graphene oxide (GO) were characterized, and the binding energies of diclofenac (DCF) and sulfamethoxazole (SMX) on GO adsorption were predicted using molecular modeling. The adsorption behaviors of DCF and SMX were investigated in terms of GO dosage, contact time, and pH. Additionally, the effects of sonication on GO adsorption were examined. GO adsorption involves ‘‘oxygen-containing functional groups’’ (OCFGs) such as ACOOH, which exhibit negative charges over a wide range of pH values (pH 3–11). DCF (18.8 kcal mol1) had a more favorable binding energy on the GO surface than SMX (15.9 kcal mol1). Both DCF and SMX were removed from solution (adsorbed to GO), up to 35% and 12%, respectively, within 6 h, and an increase in GO dosage enhanced the removal of DCF. Electrostatic repulsion occurred between dissociated DCF/SMX and the more negatively charged GO at basic pH (>pKa). The sonication of GO significantly improved the removal of DCF (75%) and SMX (30%) due to dispersion of exfoliated GO particles and the reduction of OCFGs on the GO surface. Both DCF and SMX in the adsorption isotherm were explained well by the Freundlich model. The results of this study can be used to maximize the adsorption capacities of micropollutants using GO in water treatment processes. Ó 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding authors. Tel.: +82 2 880 2737; fax: +82 2 762 2888 (K.-D. Zoh). Tel.: +1 803 777 8952; fax: +1 803 777 0670 (Y. Yoon). E-mail addresses: [email protected] (K.-D. Zoh), [email protected] (Y. Yoon). http://dx.doi.org/10.1016/j.chemosphere.2015.03.061 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.

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S.-W. Nam et al. / Chemosphere 136 (2015) 20–26

1. Introduction Over recent decades, emerging micropollutants such as pharmaceuticals have become a concern in water and wastewater treatment plants. Although they occur at trace levels (sub lg L1) in drinking water sources and wastewater effluents, their bioaccumulation in aquatic creatures causes continuous human exposure through the food chain (Sharma et al., 2003; Daneshvar et al., 2010). Among numerous pharmaceuticals commonly detected in drinking water sources and wastewater effluents, diclofenac (DCF) and sulfamethoxazole (SMX) are representative micropollutants that are readily released into the water environment, and are detected frequently in drinking water (Feito et al., 2010; Santos et al., 2010; Yiruhan et al., 2010; Li et al., 2010a; Huerta-Fontela et al., 2011). DCF is a nonsteroidal anti-inflammatory drug used for fever and pain relief, and SMX is an antimicrobial drug, commonly used in humans and animals. Previous studies have reported that DCF and SMX may potentially cause adverse effects such as thyroid tumors and hemodynamic changes with chronic human exposure (Collier, 2007; Schriks et al., 2010). Since ‘conventional’ water and wastewater treatment plants are not optimized for the removal of such trace compounds, DCF and SMX have been reported in drinking water (Collier, 2007). Thus, it is important to develop effective technologies to remove these compounds from drinking water. Adsorption is known as an effective treatment technique for the removal of organic micropollutants such as pharmaceuticals and pesticides (Adams et al., 2002; Westerhoff et al., 2005; Snyder et al., 2007). Conventional and emerging adsorbents (e.g., activated carbon and carbon nanotubes, CNTs) have thus been studied widely regarding the removal of micropollutants (Yu et al., 2008; Joseph et al., 2011; Sotelo et al., 2011). However, these adsorbents have unique physical and chemical properties (e.g., hydrophobicity, chemical functional groups, pore size, external surface area, and point of zero charge), which may not be suitable for certain compounds to attach to the surface of the adsorbents. For example, it has been reported that activated carbon can exclude the adsorption of larger molecules (>3000 Da) due to its small pore ( 99%) was purchased from Cheap Tubes, Inc. (Brattleboro, VT, USA). As described by the manufacturer, the X and Y dimensions for standard GO particles are in the range of 300800 nm with a thickness of 0.71.2 nm. Pristine GO was produced by oxidation from graphite using a modified Hummer method (Chen et al., 2009). To modify the adsorbent, sonication for GO was carried out at 12 and 24 W for 10 min with a Misonix S4000 sonicator (Farmingdale, NY, USA). All GO stock solutions were prepared at 1 g L1 of deionized (DI) water. These solutions were stirred at room temperature for 24 h prior to use, because hydration is needed to activate the surface of GO. DCF (purity > 99%) and SMX (purity > 99%) were obtained from Sigma–Aldrich (St. Louis, MO, USA). As necessary, stock solutions were diluted for the experiments. The physicochemical properties of DCF and SMX are described in Table S1. 2.2. Adsorption experiments Kinetic batch tests were performed with 100 mg L1 of the GO stock solution diluted to 10–100 mg L1. The testing jar of GO solution was stirred at 600 rpm during the experiments, and surrounded by aluminum foil to prevent photo-degradation of the target compounds. The initial concentrations of DCF and SMX were maintained at 10 lM by spiking of the GO stock solution, and confirmed by measuring control samples when the test started. Then, aliquots of the tested solution were withdrawn from the testing jar at time points of 0, 0.5, 1, 2, 4, 6, and 24 h. The tested samples were filtered through a 0.22-lm Durapore membrane filter (Millipore, Cork, Ireland), and analyzed by high-performance liquid chromatography (HPLC). The detailed HPLC measurement conditions are described in more detail (see Section 2.3). Adsorption on the sonicated GO was completed by the same process. The pH conditions in the solutions were adjusted with 1 N NaOH or HCl, and monitored with a pH meter during the experiments. In this study, the adsorption isotherms for DCF and SMX were completed individually in amber vials, and the total volumes of each test solutions were 40 mL including 100 mg L1 of GO. There was no head space in the test vials. They were adjusted to neutral pH (pH 7), and the vials were stirred at 60 rpm for 2 d. The initial concentrations of DCF and SMX ranged from 10 to 300 lM. During the test, room temperature was maintained at 20 °C. The isotherm results for the compounds were fitted to the Freundlich (Eq. (1)), and Langmuir models (Eq. (2)). The relevant equations of the adsorption models are as follows: 1

qe ¼ K F C en

ð1Þ

qe ¼ ðqmax K L C e Þ=ð1 þ K L C e Þ

ð2Þ 1

where qe is the equilibrium adsorption capacity (mg g ), KF is the Freundlich adsorption coefficient ((mg g1) (mg L1)(1/n)), Ce is

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S.-W. Nam et al. / Chemosphere 136 (2015) 20–26

the equilibrated concentration (mg L1), 1/n is the Freundlich intensity parameter, qmax is the maximum adsorption capacity (mg g1), and KL is the Langmuir adsorption coefficient (L mg1).

DCF interacted more favorably with the graphitic structure than SMX (18.8 vs. 15.9 kcal mol1) due to the greater surface area exposure to the GO, which resulted in increased p–p EDA interactions and dispersion forces between the adsorbent and DCF.

2.3. Analytical methods 3.3. Role of dosage and contact time in adsorption

3. Results and discussions 3.1. Characterization of GO Pristine GO in solution readily showed aggregation between particles that then settle on the bottom of the testing beaker (Fig. S1). In fact, GO particles in the stock solution were maintained as aggregated clusters, with an average hydrodynamic radius of >20 lm. The size distribution of GO clusters is described in Section 3.4. As shown in Fig. S2a, we confirmed the size of the individual GO particles using AFM. The cross-sectional diameter of GO particles was 2.5) (Adams

(a)

0.6 0.4 GO= 10 mg L-1

0.2

GO= 50 mg L-1 GO= 100 mg L-1

0.0 0

6

12

18

24

Time (h)

(b)

1.0 0.8

C/C0

3.2. Binding energies of the compounds on the GO adsorption The configurations of the GO–DCF and GO–SMX optimized at the DFT-D/BLYP/6-31++G (d,p) level are shown in Fig. S3. The main adsorption mechanism of the compounds onto GO was due to hydrophobic interactions and p–p electron donor acceptor (EDA) interactions. In the lowest energy configuration, both DCF and SMX interacted with the graphitic structure at a minimum intermolecular distance of 3.5 Å. The amine aromatic ring in SMX was oriented parallel to the surface of the GO, while the second ring was oriented away from the GO surface. In the case of the GO–DCF complex, both aromatic rings were oriented towards the surface of the GO, with the second ring slightly oriented at an angle, maximizing p–p EDA interactions between DCF and GO.

1.0 0.8

C/C0

DCF and SMX in the test solution were analyzed with an HPLC 1200 Series (Agilent Technologies, Santa Clara, CA, USA) equipped with an ultra-violet (UV) detector and a LiChrosper RP-18 column (4.6  150 mm, 5 lm, Agilent, Santa Clara, CA, USA). The isocratic mobile phase consisted of 50:50 (v/v%) acetonitrile:water with 5 mM phosphoric acid. The flow rate was 0.75 mL min1 for 13 min. The wavelength of the UV detector was set at 210 nm, and DCF and SMX separated from the column at 10.6 and 3.8 min, respectively.

0.6 0.4 GO= 10 mg L-1

0.2

-1

GO= 50 mg L

GO= 100 mg L

0.0 0

6

12

18

-1

24

Time (h) Fig. 1. Adsorption of (a) DCF and (b) SMX on GO as a function of GO concentration and contact time. Error bars were calculated based on standard deviation (n = 3; C0 = 10 lM; pH = 7; temperature = 20 °C; contact time = 0–24 h).

S.-W. Nam et al. / Chemosphere 136 (2015) 20–26

et al., 2002; Ternes et al., 2002; Benotti et al., 2008; Nakada et al., 2008). An increase in GO concentration in the test solution provides a larger adsorbable surface of adsorbent to the relatively hydrophobic DCF, while SMX (log KOW = 0.79) was not appropriate for hydrophobic adsorption, due to its hydrophilic properties. Another possible mechanism for GO adsorption, the electrostatic interaction between the compounds and GO, was not considered in this study, because both DCF and SMX have negative charges at pH 7 and thus both electric repulsion and attraction may coexist. Therefore, any electrostatic interaction was difficult to interpret at the pH used in this study. The p energy level of individual organic chemicals can sensitively affect the p–p EDA interaction between adsorbates and carbonaceous adsorbents (Yang et al., 2010; Ji et al., 2010b; Jung et al., 2013). Both DCF and SMX have two separate benzene rings in their chemical structure, and also exhibit similar p energies, 33.2 and 30.9, respectively (Table S1). Although the molecular modeling predicted the electron affinity for aromatic rings between the compounds and GO qualitatively, the p energies of the adsorbates suggest that the p–p EDA interaction had no significant relationship with compound adsorption. These results indicate that the hydrophobic interaction was the most appropriate of the possible mechanisms to explain GO adsorption. In addition, the findings also showed that an increase in GO concentration was more effective in terms of adsorption of these compounds than extension of the contact time. 3.4. Effects of pH on adsorption Ionizable micropollutants can interact with adsorbents through electrostatic attraction or repulsion, depending on their pKa values (Bajpai and Rajpoot, 1996; Ternes et al., 2002; Westerhoff et al., 2005; Huerta-Fontela et al., 2011). Several adsorption experiments were conducted to confirm the removal of the compounds in a wide range of pH values, pH 3–11. As shown in Fig. 2, the removal of the compounds was greater under acidic conditions (pH < pKa) than at basic pH (pH > pKa). DCF (pKa, 4.15) and SMX (pKa, 5.7) have neutral ion species at acidic pH and can have more affinity with GO in adsorption than at basic pH values (Llinàs et al., 2007; Beltrán et al., 2009; Brillas et al., 2010; Teixidó et al., 2011). Thus, compound removal under acidic pH conditions is affected mainly by attraction, such as hydrophobic effects and p–p EDA interactions. However, the compounds lost protons at pH > pKa, and electric repulsion occurred between dissociated (anionic) compounds and negatively charged GO over a wide range of pH values (see Fig. S2d). The OCFGs have negative charges on the adsorptive sites of the GO surface, as described previously, which may disturb adsorption. Regarding compound adsorption in terms

1.0

C/C0

0.8 0.6

DCF pKa= 4.15

0.4 0.2

SMX pKa= 5.7

DCF SMX

0.0 3

5

7

9

11

pH Fig. 2. Adsorption of DCF and SMX on GO as a function of pH. Error bars were calculated based on standard deviation (n = 3; C0 = 10 lM; GO = 100 mg L1; temperature = 20 °C; contact time = 24 h).

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of chemical structure, polar functional groups such as hydroxyl, amine, and sulfonyl groups on DCF and SMX exhibit electron-withdrawing at basic pH values (Ji et al., 2010a). The presence of these groups can cause ‘rejection’ of the aromatic rings in GO as p electron acceptors (Hu and Mi, 2013; Jung et al., 2013; Wang et al., 2014). Thus, the chemical properties of both the compounds and GO play a significant role in the inhibition of p–p EDA interactions. Removal of the compounds was inhibited as the solution pH became more basic. Fig. 2 also shows that DCF (log KOW = 4.26) removal was greater than that of SMX (log KOW = 0.79) regardless of pH. As mentioned previously, hydrophobic attraction between the compounds and GO was the dominant adsorption mechanism. SMX thus showed less adsorption on GO due to its relatively low hydrophobicity. Although the adsorption of the compounds was affected by electric repulsion, the hydrophobic effect was a crucial removal mechanism for both DCF and SMX in terms of adsorption to GO. 3.5. Adsorption of DCF and SMX on sonicated GO Adsorption by pristine GO showed low ( pKa, and protonated OCFGs resulted in the rejection of p–p EDA on the GO surface. Sonication simultaneously caused the dispersion of GO particles and the reduction of OCFGs on the GO surface. This modification of GO enhanced the removal of the compounds through the enlargement of adsorptive area and alleviation of electric repulsion. The Freundlich isotherm fitted the adsorption of the compounds. Sonication elevated the sorption potential of GO and increased the amount of the adsorbed pollutant. SMX exhibited a slightly linear trend in GO adsorption. For hydrophilic micropollutants, it is necessary to develop appropriate adsorption models independently. Acknowledgements This research was supported by a Grant (code 14IFIP-B08738501) from Industrial Facilities & Infrastructure Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government. This research was also supported by the International Research & Development Program of the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (MEST) of Korea (NRF2012K1A3A1A12054908). 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. 2015.03.061. References Adams, C., Wang, Y., Loftin, K., Meyer, M., 2002. Removal of antibiotics from surface and distilled water in conventional water treatment processes. J. Environ. Eng. 128, 253–260. Ai, L., Zhang, C., Chen, Z., 2011. Removal of methylene blue from aqueous solution by a solvothermal-synthesized graphene/magnetite composite. J. Hazard. Mater. 192, 1515–1524. Apul, O.G., Wang, Q., Zhou, Y., Karanfil, T., 2013. Adsorption of aromatic organic contaminants by graphene nanosheets: comparison with carbon nanotubes and activated carbon. Water Res. 47, 1648–1654. Ataca, C., Aktürk, E., Ciraci, S., Ustunel, H., 2008. High-capacity hydrogen storage by metallized graphene. Appl. Phys. Lett. 93, 043123. Bajpai, A.K., Rajpoot, M., 1996. Adsorption behavior of sulfamethoxazole onto an alumina-solution interface. Bull. Chem. Soc. Jpn. 69, 521–527. Becerril, H.A., Mao, J., Liu, Z., Stoltenberg, R.M., Bao, Z., Chen, Y., 2008. Evaluation of solution-processed reduced graphene oxide films as transparent conductors. ACS Nano 2, 463–470. Beltrán, F.J., Pocostales, P., Alvarez, P., Oropesa, A., 2009. Diclofenac removal from water with ozone and activated carbon. J. Hazard. Mater. 163, 768–776. Benotti, M.J., Trenholm, R.A., Vanderford, B.J., Holady, J.C., Stanford, B.D., Snyder, S.A., 2008. Pharmaceuticals and endocrine disrupting compounds in US drinking water. Environ. Sci. Technol. 43, 597–603. Brillas, E., Garcia-Segura, S., Skoumal, M., Arias, C., 2010. Electrochemical incineration of diclofenac in neutral aqueous medium by anodic oxidation using Pt and boron-doped diamond anodes. Chemosphere 79, 605–612. Chen, C., Yang, Q.H., Yang, Y., Lv, W., Wen, Y., Hou, P.X., Wang, M., Cheng, H.M., 2009. Self-assembled free-standing graphite oxide membrane. Adv. Mater. 21, 3007– 3011. Collier, A.C., 2007. Pharmaceutical contaminants in potable water: potential concerns for pregnant women and children. EcoHealth 4, 164–171. Daneshvar, A., Svanfelt, J., Kronberg, L., Weyhenmeyer, G.A., 2010. Winter accumulation of acidic pharmaceuticals in a Swedish river. Environ. Sci. Pollut. R. 17, 908–916. Dreyer, D.R., Park, S., Bielawski, C.W., Ruoff, R.S., 2010. The chemistry of graphene oxide. Chem. Soc. Rev. 39, 228–240. Elias, D., Nair, R., Mohiuddin, T., Morozov, S., Blake, P., Halsall, M., Ferrari, A., Boukhvalov, D., Katsnelson, M., Geim, A., 2009. Control of graphene’s properties by reversible hydrogenation: evidence for graphane. Science 323, 610–613. Feito, R., Rubio, J.C.M., Fernández, J., 2010. Occurrence of pharmaceuticals in river and tap waters of Toledo (Castilla-La Mancha Community, Spain). Toxicol. Lett. 196, S61–S62.

25

Gómez-Navarro, C., Weitz, R.T., Bittner, A.M., Scolari, M., Mews, A., Burghard, M., Kern, K., 2007. Electronic transport properties of individual chemically reduced graphene oxide sheets. Nano Lett. 7, 3499–3503. Hu, M., Mi, B., 2013. Enabling graphene oxide nanosheets as water separation membranes. Environ. Sci. Technol. 47, 3715–3723. Huerta-Fontela, M., Galceran, M.T., Ventura, F., 2011. Occurrence and removal of pharmaceuticals and hormones through drinking water treatment. Water Res. 45, 1432–1442. Hyung, H., Fortner, J.D., Hughes, J.B., Kim, J.-H., 2007. Natural organic matter stabilizes carbon nanotubes in the aqueous phase. Environ. Sci. Technol. 41, 179–184. Ji, L., Chen, W., Xu, Z., Zheng, S., Zhu, D., 2013. Graphene nanosheets and graphite oxide as promising adsorbents for removal of organic contaminants from aqueous solution. J. Environ. Qual. 42, 191–198. Ji, L., Liu, F., Xu, Z., Zheng, S., Zhu, D., 2010a. Adsorption of pharmaceutical antibiotics on template-synthesized ordered micro-and mesoporous carbons. Environ. Sci. Technol. 44, 3116–3122. Ji, L., Shao, Y., Xu, Z., Zheng, S., Zhu, D., 2010b. Adsorption of monoaromatic compounds and pharmaceutical antibiotics on carbon nanotubes activated by KOH etching. Environ. Sci. Technol. 44, 6429–6436. Joseph, L., Boateng, L.K., Flora, J.R., Park, Y.-G., Son, A., Badawy, M., Yoon, Y., 2013. Removal of bisphenol A and 17a-ethinyl estradiol by combined coagulation and adsorption using carbon nanomaterials and powdered activated carbon. Sep. Purif. Technol. 107, 37–47. Joseph, L., Heo, J., Park, Y.-G., Flora, J.R., Yoon, Y., 2011. Adsorption of bisphenol A and 17a-ethinyl estradiol on single walled carbon nanotubes from seawater and brackish water. Desalination 281, 68–74. Jung, C., Park, J., Lim, K.H., Park, S., Heo, J., Her, N., Oh, J., Yun, S., Yoon, Y., 2013. Adsorption of selected endocrine disrupting compounds and pharmaceuticals on activated biochars. J. Hazard. Mater. 263, 702–710. Kilduff, J.E., Karanfil, T., Chin, Y.-P., Weber, W.J., 1996. Adsorption of natural organic polyelectrolytes by activated carbon: a size-exclusion chromatography study. Environ. Sci. Technol. 30, 1336–1343. Li, X., Ying, G.-G., Su, H.-C., Yang, X.-B., Wang, L., 2010a. Simultaneous determination and assessment of 4-nonylphenol, bisphenol A and triclosan in tap water, bottled water and baby bottles. Environ. Int. 36, 557–562. Li, X., Zhu, H., Wang, K., Cao, A., Wei, J., Li, C., Jia, Y., Li, Z., Li, X., Wu, D., 2010b. Graphene-on-silicon Schottky junction solar cells. Adv. Mater. 22, 2743–2748. Liu, Y., Dong, X., Chen, P., 2012. Biological and chemical sensors based on graphene materials. Chem. Soc. Rev. 41, 2283–2307. Llinàs, A., Burley, J.C., Box, K.J., Glen, R.C., Goodman, J.M., 2007. Diclofenac solubility: independent determination of the intrinsic solubility of three crystal forms. J. Med. Chem. 50, 979–983. Machida, M., Mochimaru, T., Tatsumoto, H., 2006. Lead (II) adsorption onto the graphene layer of carbonaceous materials in aqueous solution. Carbon 44, 2681–2688. Mishra, A.K., Ramaprabhu, S., 2011. Functionalized graphene sheets for arsenic removal and desalination of sea water. Desalination 282, 39–45. Nakada, N., Yamashita, N., Miyajima, K., Suzuki, Y., Tanaka, H., Shinohara, H., Takada, H., Sato, N., Suzuki, M., Ito, M., 2008. Multiple evaluation of soil aquifer treatment for water reclamation using instrumental analysis and bioassay. Southeast Asian Water Environ. 2, 303. Nam, S.-W., Choi, D.-J., Kim, S.-K., Her, N., Zoh, K.-D., 2014. Adsorption characteristics of selected hydrophilic and hydrophobic micropollutants in water using activated carbon. J. Hazard. Mater. 270, 144–152. Paredes, J., Villar-Rodil, S., Martinez-Alonso, A., Tascon, J., 2008. Graphene oxide dispersions in organic solvents. Langmuir 24, 10560–10564. Santos, L.H., Araújo, A., Fachini, A., Pena, A., Delerue-Matos, C., Montenegro, M., 2010. Ecotoxicological aspects related to the presence of pharmaceuticals in the aquatic environment. J. Hazard. Mater. 175, 45–95. Schriks, M., Heringa, M.B., van der Kooi, M.M., de Voogt, P., van Wezel, A.P., 2010. Toxicological relevance of emerging contaminants for drinking water quality. Water Res. 44, 461–476. Schwierz, F., 2010. Graphene transistors. Nat. Nanotechnol. 5, 487–496. Sharma, H., Trivedi, R., Akolkar, P., Gupta, A., 2003. Micropollutants levels in macroinvertebrates collected from drinking water sources of Delhi, India. India. Int. J. Environ. Stud. 60, 99–110. Snyder, S.A., Adham, S., Redding, A.M., Cannon, F.S., DeCarolis, J., Oppenheimer, J., Wert, E.C., Yoon, Y., 2007. Role of membranes and activated carbon in the removal of endocrine disruptors and pharmaceuticals. Desalination 202, 156– 181. Sotelo, J., Rodríguez, A., Álvarez, S., García, J., 2011. Removal of caffeine and diclofenac on activated carbon in fixed bed column. Chem. Eng. Res. Des. 90, 967–974. Teixidó, M., Pignatello, J.J., Beltrán, J.L., Granados, M., Peccia, J., 2011. Speciation of the ionizable antibiotic sulfamethazine on black carbon (biochar). Environ. Sci. Technol. 45, 10020–10027. Ternes, T.A., Meisenheimer, M., McDowell, D., Sacher, F., Brauch, H.-J., Haist-Gulde, B., Preuss, G., Wilme, U., Zulei-Seibert, N., 2002. Removal of pharmaceuticals during drinking water treatment. Environ. Sci. Technol. 36, 3855–3863. Wang, C., Li, H., Liao, S., Zheng, H., Wang, Z., Pan, B., Xing, B., 2013. Coadsorption, desorption hysteresis and sorption thermodynamics of sulfamethoxazole and carbamazepine on graphene oxide and graphite. Carbon 65, 243–251. Wang, J., Chen, Z., Chen, B., 2014. Adsorption of polycyclic aromatic hydrocarbons by graphene and graphene oxide nanosheets. Environ. Sci. Technol. 48, 4817– 4825.

26

S.-W. Nam et al. / Chemosphere 136 (2015) 20–26

Westerhoff, P., Yoon, Y., Snyder, S., Wert, E., 2005. Fate of endocrine-disruptor, pharmaceutical, and personal care product chemicals during simulated drinking water treatment processes. Environ. Sci. Technol. 39, 6649–6663. Yang, K., Wu, W., Jing, Q., Jiang, W., Xing, B., 2010. Competitive adsorption of naphthalene with 2, 4-dichlorophenol and 4-chloroaniline on multiwalled carbon nanotubes. Environ. Sci. Technol. 44, 3021–3027. Yiruhan, Wang, Q.-J., Mo, C.-H., Li, Y.-W., Gao, P., Tai, Y.-P., Zhang, Y., Ruan, Z.-L., Xu, J.-W., 2010. Determination of four fluoroquinolone antibiotics in tap water in Guangzhou and Macao. Environ. Pollut. 158, 2350–2358.

Yu, Z., Peldszus, S., Huck, P.M., 2008. Adsorption characteristics of selected pharmaceuticals and an endocrine disrupting compound—Naproxen, carbamazepine and nonylphenol—on activated carbon. Water Res. 42, 2873– 2882. Zhang, K., Kemp, K.C., Chandra, V., 2012. Homogeneous anchoring of TiO2 nanoparticles on graphene sheets for waste water treatment. Mater. Lett. 81, 127–130. Zhao, G., Li, J., Ren, X., Chen, C., Wang, X., 2011. Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management. Environ. Sci. Technol. 45, 10454–10462.