Adsorption of 4- n -Nonylphenol and Bisphenol-A on Magnetic Reduced Graphene Oxides: A Combined Experimental and Theoretical Studiesby Zhongxiu Jin, Xiangxue Wang, Yubing Sun, Yuejie Ai, Xiangke Wang

Environmental Science & Technology

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Year
2015
DOI
10.1021/acs.est.5b02022
Subject
Chemistry (all) / Environmental Chemistry

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Adsorption of 4-n-Nonylphenol and Bisphenol-A on Magnetic Reduced 1

Graphene Oxides: A Combined Experimental and Theoretical Studies 2

Zhongxiu Jin 1,2,3 , Xiangxue Wang 2,3 , Yubing Sun 2* , Yuejie Ai 1 *, Xiangke 3

Wang 1,4,5 * 4 1. School of Environment and Chemical Engineering, North China Electric Power 5

University, Beijing 102206, P. R. China 6 2. Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, 7

Chinese Academy of Science, P.O. Box 1126, Hefei, 230031, P.R. China 8 3. University of Science and Technology of China, Hefei, 230032, P.R. China 9 4. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher 10

Education Institutions and School for Radiological and Interdisciplinary Sciences, 11

Soochow University, 215123, Suzhou, P.R. China 12 5. NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 13 21589, Saudi Arabia 14 *: Corresponding authors. Email: sunyb@ipp.ac.cn (Y. Sun); aiyuejie314@126.com 15 (Y. Ai); xkwang@ipp.ac.cn or xkwang@ncepu.edu.cn (X. Wang); Tel: 16 +86-10-61772890; Fax: +86-10-61772890. 17

ABSTRACT 18

Adsorption of 4-n-nonylphenol (4-n-NP) and bisphenol-A (BPA) on magnetic reduced 19 graphene oxides (rGOs) as a function of contact time, pH, ionic strength and humic 20 acid were investigated by batch techniques. Adsorption of 4-n-NP and BPA were 21 independent of pH at 3.0- 8.0, whereas the slightly decreased adsorption was observed 22

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Environmental Science & Technology 2 / 33 at pH 8.0-11.0. Adsorption kinetics and isotherms of 4-n-NP and BPA on magnetic 23 rGOs can be satisfactorily fitted by pseudo-second-order kinetic and Freundlich 24 model, respectively. The maximum adsorption capacities of magnetic rGOs at pH 6.5 25 and 293 K were 63.96 and 48.74 mg/g for 4-n-NP and BPA, respectively, which were 26 significantly higher than that of activated carbon. Based on theoretical calculations, 27 the higher adsorption energy of rGOs + 4-n-NP was mainly due to π-π stacking and 28 flexible long alkyl chain of 4-n-NP, whereas adsorption of BPA on rGOs was 29 energetically favored by a lying-down configuration due to π-π stacking and 30 dispersion forces, which was further demonstrated by FTIR analysis. These findings 31 indicate that magnetic rGOs is a promising adsorbent for the efficient elimination of 32 4-n-NP/BPA from aqueous solutions due to its excellent adsorption performance and 33 simple magnetic separation, which are of great significance for the remediation of 34 endocrine-disrupting chemicals in environmental cleanup. 35

INTRODUCTION 36

Endocrine-disrupting chemicals (EDCs) such as 4-n-nonylphenol (4-n-NP) and 37 bisphenol-A (BPA) affect the growth and reproduction of many species even at very 38 low concentrations.1 It is demonstrated that 4-n-NP is the degradation products of 39 nonylphenol ethoxylates, which is extensively used to synthesize the detergents, 40 paints, lubricants, resins, and pesticides.2 BPA is used to make epoxy resins and 41 polycarbonate plastics, which has been linked to prostate and breast cancer, birth 42 defects, miscarriages, obesity, premature development in girls, polycystic ovarian 43 syndrome, and hypertension, among other conditions.3–8 4-n-NP and BPA have been 44

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Environmental Science & Technology 3 / 33 widely detected in various organic wastewaters worldwide.9 Therefore, the removal of 45 4-n-NP and BPA from contaminated wastewater is becoming an important issue in 46 environmental pollution and wastewater purification. It is reported that the removal of 47 4-n-NP and BPA can be used by various techniques such as photocatalysis, 48 molecular-imprinted approaches, biodegradation and adsorption approaches.10-13 49

Among these methods, adsorption technique has been widely applied to remove 50 4-n-NP and BPA due to the low cost, simple operation and high efficiency. The 51 adsorption of 4-n-NP and BPA on carbon nanotubes12 and activated carbon14, 15 has 52 been extensively investigated in recent years. A variety of adsorption mechanisms 53 have been recently proposed such as hydrophobicity, hydrogen bonding, π-π 54 interactions and morphology change.16-21 To the author’s knowledge, few 55 investigations on the adsorption of 4-n-NP and BPA on graphene-based nanomaterials 56 are available.22-24 57

Graphene oxides (GOs), a two dimensional carbon-based material, has been 58 extensively investigated to remove organic contaminants in environmental pollution 59 cleanup due to its large specific surface area and a variety of oxygenated functional 60 groups.25 GOs and reduced GOs (rGOs) have already been used as adsorbents for the 61 removal of various environmental contaminants.26-32 Xu et al.23 found that the rGOs 62 presented very high adsorption capacity for BPA (approximately 85 mg/g at pH 7.0 63 and 298 K). However, GOs are difficult to separate from water due to its excellent 64 dispersibility, which could lead to new environmental risks.33 Magnetic GOs combine 65 the high adsorption capacity of the GOs and the separation convenience of the 66

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Environmental Science & Technology 4 / 33 magnetic properties, which is potentially helpful for the real applications.34-36 67

Herein, the magnetic rGOs were synthesized and applied to remove 4-n-NP and BPA 68 from aqueous solutions. The objectives of this paper are (1) to investigate the effect of 69 contact time, pH, ionic strength, humic acid (HA) on 4-n-NP and BPA adsorption onto 70 rGOs and magnetic rGOs by batch techniques; and (2) to perform the interaction 71 mechanism between rGOs/magnetic rGOs and EDCs by FTIR analysis, SEM 72 characterization and theoretical calculations. It is a highlight of this study to 73 demonstrate the different interaction mechanism of BPA and 4-n-NP on rGOs by 74 using density functional theory (DFT) calculations. The investigation on the 75 adsorption of 4-n-NP and BPA at water-solid interface is conducive to the prediction 76 of the fate and transport of EDCs in aquatic environments. 77