Nonylphenol and Bisphenol-A on Magnetic ... - ACS Publications

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Environmental Science & Technology 1 / 33

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

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Graphene Oxides: A Combined Experimental and Theoretical Studies Zhongxiu Jin1,2,3, Xiangxue Wang2,3, Yubing Sun2*, Yuejie Ai1*, Xiangke

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Wang1,4,5*

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1. School of Environment and Chemical Engineering, North China Electric Power University, Beijing 102206, P. R. China

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2. Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Science, P.O. Box 1126, Hefei, 230031, P.R. China

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University of Science and Technology of China, Hefei, 230032, P.R. China

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4. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher

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Education Institutions and School for Radiological and Interdisciplinary Sciences,

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Soochow University, 215123, Suzhou, P.R. China

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5. NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia

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*: Corresponding authors. Email: [email protected] (Y. Sun); [email protected]

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(Y. Ai); [email protected] or [email protected] (X. Wang); Tel:

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+86-10-61772890; Fax: +86-10-61772890.

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ABSTRACT

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Adsorption of 4-n-nonylphenol (4-n-NP) and bisphenol-A (BPA) on magnetic reduced

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graphene oxides (rGOs) as a function of contact time, pH, ionic strength and humic

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acid were investigated by batch techniques. Adsorption of 4-n-NP and BPA were

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independent of pH at 3.0- 8.0, whereas the slightly decreased adsorption was observed

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at pH 8.0-11.0. Adsorption kinetics and isotherms of 4-n-NP and BPA on magnetic

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rGOs can be satisfactorily fitted by pseudo-second-order kinetic and Freundlich

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model, respectively. The maximum adsorption capacities of magnetic rGOs at pH 6.5

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and 293 K were 63.96 and 48.74 mg/g for 4-n-NP and BPA, respectively, which were

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significantly higher than that of activated carbon. Based on theoretical calculations,

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the higher adsorption energy of rGOs + 4-n-NP was mainly due to π-π stacking and

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flexible long alkyl chain of 4-n-NP, whereas adsorption of BPA on rGOs was

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energetically favored by a lying-down configuration due to π-π stacking and

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dispersion forces, which was further demonstrated by FTIR analysis. These findings

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indicate that magnetic rGOs is a promising adsorbent for the efficient elimination of

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4-n-NP/BPA from aqueous solutions due to its excellent adsorption performance and

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simple magnetic separation, which are of great significance for the remediation of

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endocrine-disrupting chemicals in environmental cleanup.

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INTRODUCTION

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Endocrine-disrupting chemicals (EDCs) such as 4-n-nonylphenol (4-n-NP) and

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bisphenol-A (BPA) affect the growth and reproduction of many species even at very

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low concentrations.1 It is demonstrated that 4-n-NP is the degradation products of

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nonylphenol ethoxylates, which is extensively used to synthesize the detergents,

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paints, lubricants, resins, and pesticides.2 BPA is used to make epoxy resins and

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polycarbonate plastics, which has been linked to prostate and breast cancer, birth

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defects, miscarriages, obesity, premature development in girls, polycystic ovarian

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syndrome, and hypertension, among other conditions.3–8 4-n-NP and BPA have been


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widely detected in various organic wastewaters worldwide.9 Therefore, the removal of

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4-n-NP and BPA from contaminated wastewater is becoming an important issue in

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environmental pollution and wastewater purification. It is reported that the removal of

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4-n-NP and BPA can be used by various techniques such as photocatalysis,

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molecular-imprinted approaches, biodegradation and adsorption approaches.10-13

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Among these methods, adsorption technique has been widely applied to remove

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4-n-NP and BPA due to the low cost, simple operation and high efficiency. The

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adsorption of 4-n-NP and BPA on carbon nanotubes12 and activated carbon14, 15 has

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been extensively investigated in recent years. A variety of adsorption mechanisms

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have been recently proposed such as hydrophobicity, hydrogen bonding, π-π

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interactions and morphology change.16-21 To the author’s knowledge, few

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investigations on the adsorption of 4-n-NP and BPA on graphene-based nanomaterials

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are available.22-24

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Graphene oxides (GOs), a two dimensional carbon-based material, has been

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extensively investigated to remove organic contaminants in environmental pollution

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cleanup due to its large specific surface area and a variety of oxygenated functional

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groups.25 GOs and reduced GOs (rGOs) have already been used as adsorbents for the

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removal of various environmental contaminants.26-32 Xu et al.23 found that the rGOs

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presented very high adsorption capacity for BPA (approximately 85 mg/g at pH 7.0

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and 298 K). However, GOs are difficult to separate from water due to its excellent

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dispersibility, which could lead to new environmental risks.33 Magnetic GOs combine

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the high adsorption capacity of the GOs and the separation convenience of the



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magnetic properties, which is potentially helpful for the real applications.34-36

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Herein, the magnetic rGOs were synthesized and applied to remove 4-n-NP and BPA

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from aqueous solutions. The objectives of this paper are (1) to investigate the effect of

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contact time, pH, ionic strength, humic acid (HA) on 4-n-NP and BPA adsorption onto

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rGOs and magnetic rGOs by batch techniques; and (2) to perform the interaction

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mechanism between rGOs/magnetic rGOs and EDCs by FTIR analysis, SEM

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characterization and theoretical calculations. It is a highlight of this study to

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demonstrate the different interaction mechanism of BPA and 4-n-NP on rGOs by

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using density functional theory (DFT) calculations. The investigation on the

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adsorption of 4-n-NP and BPA at water-solid interface is conducive to the prediction

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of the fate and transport of EDCs in aquatic environments.

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EXPERIMENTAL SECTION

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Materials. Flake graphite (48 µm, 99.95% purity) was purchased from Qingdao

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Tianhe graphite Co., Ltd. BPA (> 99.8 % purity) and 4-n-NP (>99 % purity) were

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obtained from Sigma-Aldrich and Dr. Ehrenstorfer Standard (Germany), respectively.

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The 4-n-NP and BPA stock solutions (2.5 g/L) were prepared by dissolving them in

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LC-MS grade acetonitrile (Honeywell) and then were diluted using LC-MS grade

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water (Honeywell). The selected physicochemical properties of BPA and 4-n-NP

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were summarized in Table S1 in the Supporting Information (SI). HA was extracted

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from the soil of Hua-Jia county (Gansu province, China). As shown in Table S2, the

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main components of HA were C (~ 60 wt %), O (31 wt %), N (4.21 wt %) and S (0.52

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wt%), revealing a variety of oxygen-, nitrogen- and sulfur- containing functional


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groups. The small amount of acetonitrile (< 0.10 %) was used to avoid co-solvent

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effects in this study. All other chemicals of analytic reagents were purchased from

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Sinopharm Chemical Reagent Co., Ltd.

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Synthesis of Magnetic rGOs. The GOs and rGOs were firstly synthesized by using

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modified Hummers method37 and by hydrazine hydrate reduction of GOs under

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water-cooled condenser conditions, respectively.38 The more detailed procedure on

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GOs and rGOs synthesis was provided in SI. The magnetic rGOs were synthesized by

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chemical co-precipitation method.34 Typically, 0.25 g GOs were dispersed in 450 mL

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water under vigorously stirring for 30 min. Then 0.92 g FeCl3.6H2O and 0.52 g

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FeSO4.7H2O were dropwise added to GOs solution at room temperature under N2

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conditions. 30 % ammonia solution was added to adjust pH 10. Then the temperature

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of solution was raised to 90 oC, 12 mL of hydrazine hydrate was added under constant

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stirring for 4 h and then was cooled to room temperature, resulting in the color change

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from brown to black. The suspensions were washed with water and ethanol several

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times, and the magnetic rGOs were obtained by dried it in vacuum oven overnight. As

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shown in Figure S1A in SI, the saturation magnetization is calculated to be 19.16

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emu/g, indicating a high magnetism of the magnetic rGOs.

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Batch Adsorption Experiments. The adsorption experiments of 4-n-NP and BPA on

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rGOs and magnetic rGOs were carried out at pH 6.5 and 293 K using batch

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techniques. Briefly, the aliquot of 4-n-NP and BPA (0.10-2.5 mg L-1) were added into

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0.02 g/L rGOs and magnetic rGOs, respectively. The effects of ionic strength and HA

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on the adsorption of BPA and 4-n-NP on rGOs and magnetic rGOs were also



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conducted at pH 6.5 and 293 K. The pH of suspension was adjusted by adding

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negligible volumes of 0.1 mol/L HCl or NaOH solution. Then suspensions were

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vigorously stirred at 293 K for 24 h. The supernatants of magnetic rGOs system were

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separated by using a permanent magnet while rGOs system was centrifuged at 6000

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rpm for 30 min. The concentrations of 4-n-NP and BPA were analyzed using high

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performance liquid chromatography- tandem mass spectrometry (HPLC-MS/MS,

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Agilent Technologies 1200 Series for HPLC and 6410 Triple Quard. for MS). More

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details on the measurement of 4-n-NP and BPA were provided in SI. The each

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experimental data was obtained by the average values of triple parallel samples.

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Desorption of 4-n-NP and BPA from magnetic rGOs were also conducted under N2

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atmosphere to evaluate the recycling of magnetic rGOs. Briefly, the solid phases after

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adsorption equilibrium were separated from liquid phases by using a permanent

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magnet, and the BPA/4-n-NP-containing magnetic rGOs was rinsed several times by

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methanol and acetonitrile (v/v = 50: 50) under N2 atmosphere until the concentration

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of BPA and 4-n-NP in supernatant solution cannot be detected by HPLC-MS/MS. The

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obtained magnetic rGOs was reused to conduct the following adsorption experiments.

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To minimize experimental error, all laboratory glassware were soaked with potassium

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dichromate and concentrated acid solution for 24 h and then rinsed with water and

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acetone, finally glassware were baked at 400 ºC for 5 h.

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Computational Details. The interaction mechanism of 4-n-NP and BPA with

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rGOs/GOs was demonstrated by using B3LYP hybrid functional of DFT calculations

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with the 6-31G (d) basis set method.39 The optimized geometries of 4-n-NP and BPA


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were shown in Figure S2. The heterogeneous natures of magnetic rGOs make it

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particularly difficult to build molecular models. To simplify computational complexity,

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a series of finite-sized simplified molecular models of rGOs and GOs were employed

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in DFT calculations (Figure S3). The adsorption energies (Ead = ErGOs/GOs + E4-n-NP/BPA

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–ErGOs/GOs-4-n-NP/BPA) were calculated to determine the most stable structures of

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4-n-NP/BPA with rGOs/GOs. The dispersion forces and solvation effects were

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corrected by an empirical formula40 and a conductor-like polarizable continuum model

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method,41 respectively.

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RESULTS AND DISCUSSION

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Characterization. The morphologies of magnetic rGOs are characterized by SEM

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and TEM (Figure 1A and B). As shown in Figure 1A, numerous nanoparticles are

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aggregated on the surface of wrinkled rGOs tightly, and these nanoparticles are

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demonstrated to be iron oxides by EDX analysis (inset in Figure 1A). Generally, the

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intrinsic wrinkles are essential for the structural stability of GOs.42, 43 It has been

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reported that magnetic rGOs present the high chemical activity due to the nonuniform

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distribution of concentrated charge.27 The particle size of iron oxide is approximately

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50 × 50 nm according to high resolution TEM observation (Figure 1B). Figure 1C

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shows the XRD patterns of rGOs, Fe3O4 and magnetic rGOs. The weak and broad

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diffraction peak of rGOs at 2θ = 25º is attributed to the rather limited ordering in each

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rGOs and the uneven interlayer spacing over the whole rGOs sample.44 For magnetic

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rGOs, the broader diffraction peaks at 2θ = 30.21, 35.71, 43.31, 53.70, 57.35, 62.72°

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are consistent with (220), (311), (400), (422), (511), (440) plane of magnetite,



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revealing that magnetic Fe3O4 nanoparticles are synthesized by using this method. The

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surface functional groups of rGOs and magnetic rGOs are determined by FTIR

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spectroscopy. As shown in Figure 1D, the bands of rGOs at 1180, 1630 and 3456 cm-1

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are assigned to the stretching vibrations of C−O, aromatic C=C and -OH,

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respectively.28,30 For magnetic rGOs, the shifts of C=C (from 1630 to1617 cm−1) and

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C-O bands (from 1180 to 1167 cm−1) are observed, indicating that Fe3O4 nanoparticles

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could be bonded with –COOH/–OH groups of rGOs. For magnetic rGOs and Fe3O4,

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the band at 585 cm-1 is attributed to the stretching vibration of Fe-O, which is

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consistent with previous study.45

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Figure 1E shows the high-resolution XPS C1s spectra of rGOs and magnetic rGOs.

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The C1s peaks can be deconvoluted into the peaks at 284.8 (C=C), 286.6 (C-O), 287.9

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(C=O) and 289.6 eV (O-C=O), respectively.26 The relative intensities of C-O, C=O

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and O-C=O peaks of magnetic rGOs are lower than GOs, indicating that the magnetic

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rGOs are deeper reduced in this study.46 As shown in Figure 1F for Raman spectra,

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the G band of rGOs (at ~ 1348.7 cm-1) is significantly lower than that of magnetic

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rGOs (at ~ 1361 cm-1), whereas the slight increase of D band of rGOs (at ~ 1581.0

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cm-1) is observed compared to that of magnetic rGOs (at ~ 1577 cm-1). This

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phenomenon indicates that magnetic rGOs present the nano-hybrids as compared to

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rGOs, leading to the charge transfer.47 Compared to GOs, the D band of rGOs is

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shifted from 1363 cm-1 to 1352 cm-1, indicating the rGOs is deeper reduced.38 The

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ID/IG ratio is used to estimate the relative extent of structural defects.46 The value of

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ID/IG of rGOs (1.01) is higher than that of GOs (0.926), revealing a decrease in the


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average size of the sp2 domains upon reduction of the GOs.38

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Adsorption Kinetics. Figure 2 shows the adsorption kinetics of 4-n-NP and BPA onto

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rGOs and magnetic rGOs. The adsorption of 4-n-NP and BPA increases quickly in the

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first 4 h of contact time, and then achieves the adsorption equilibrium after 10 h. The

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kinetics results indicate that rGOs and magnetic rGOs possess high adsorption

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efficiency for 4-n-NP and BPA. It is noted that the adsorptions of 4-n-NP and BPA on

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rGOs are higher than magnetic rGOs, which could be due to the much lower

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adsorption capacity of the iron oxide on magnetic rGOs compared to the graphitic

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sheet. In addition, the surface area of magnetic rGOs (112.15 m2/g) is lower than that

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of rGOs (128.37 m2/g) (Table S2), indicating that some surface sites of rGOs are

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blocked by iron oxides. It is also observed that the adsorption of 4-n-NP on rGOs and

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magnetic rGOs is higher than that of BPA. The pseudo-first-order48 and

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pseudo-second-order kinetic models49 are adopted to fit the data of sorption kinetics.

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Detailed description on kinetic models is provided in Figure S4 of SI. As shown in

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Table S3, the sorption kinetics of 4-n-NP and BPA on rGOs and magnetic rGOs can

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be better fitted by pseudo-second- order kinetic model (R2 = 0.9999).

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Effect of pH and Ionic Strength. Figure 3A shows the effect of pH on the adsorption

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of 4-n-NP and BPA onto rGOs and magnetic rGOs. The adsorption of 4-n-NP and

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BPA on magnetic rGOs and rGOs is independent of pH at pH 3.0-8.0, whereas the

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slightly decreased adsorption is observed at pH 8.0-11.0. As shown in Figure S1B, the

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slightly differences in zeta potentials of rGOs and magnetic rGOs are observed at pH

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4.0 - 7.5, which are responsible for no change of the BPA and 4-n-NP adsorption at



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pH 3.0-8.0. As shown in Table S1, the pKa values of BPA and 4-n-NP are measured to

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be 8.0 and 10.7, respectively, indicating deprotonation of BPA and 4-n-NP occurs at

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pH > 8.0.50 Therefore the negative charged BPA and 4-n-NP are difficult to be

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adsorbed on the more negatively charged surface of rGOs and magnetic rGOs at

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higher pH values.

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The effect of ionic strength on 4-n-NP and BPA adsorption onto magnetic rGOs and

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rGOs is shown in Figure 3B. The slightly increased adsorption of 4-n-NP and BPA on

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rGOs and magnetic rGOs are observed with increasing NaCl concentration. The

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equilibrium adsorption amount follows the order 4-n-NP_rGOs> 4-n-NP_magnetic

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rGOs> BPA_rGOs> BPA_magnetic rGOs, which is consistent with the results of

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adsorption kinetics and pH-dependent adsorption. The increase of ionic strength at

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circumneutral conditions results in decreasing the solubility of BPA and 4-n-NP such

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as salting-outing effect. Therefore, the enhancement of the adsorption at high ionic

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strength conditions may be related with the salting-out effect of the electrolytes, not

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the electrostatic attraction.

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Effect of HA. HA is ubiquitous in aqueous solutions derived by the microbial

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degradation of dead plant matter. Figure 4 shows the isothermal adsorption of BPA

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and 4-n-NP on rGOs and magnetic rGOs in the absence and presence of HA. It is

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observed that HA inhibits the adsorption of BPA and 4-n-NP on rGOs and magnetic

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rGOs. Actually, the interaction between HA and rGO surface is complicated because

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rGOs contain both sp2 and sp3 structures. As shown in Figure S1B, HA displays

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negative zeta potential at pH > 1.5, which is attributed to the dissociation of


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carboxylic (-COOH) and phenolic (-OH) groups.51,52 However, rGOs and magnetic

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rGOs present negative zeta potential at pH > 7.0 (Figure S1B). Therefore, negatively

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charged HA at pH 6.5 is prone to bond with positive charged rGOs and magnetic

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rGOs due to electrostatic attraction, which significantly decreases reactive sites of

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rGOs and magnetic rGOs. The inhibit effect could be attributed to the competitive

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adsorption of HA and BPA/4-n-NP on magnetic rGOs. Wang et al. also reported that

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HA slightly decreased the adsorption of phenanthrene, naphthalene and 1-naphthol on

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CNTs.53 The authors demonstrated that the HA coating dramatically altered surface

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properties of CNTs, which significantly reduced the accessibility of its sorption sites.

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Adsorption Isotherms. Figure 4 shows the adsorption isotherms of 4-n-NP and BPA

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on rGOs and magnetic rGOs. The Langmuir54 and Freundlich55 models are employed

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to fit the data of adsorption isotherms. The more description and the corresponding

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parameters of Langmuir and Freundlich models are presented in Table S4. It can be

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seen from Figure 4 and Table S4 that the Freundlich model gives a somewhat better fit

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than the Langmuir model. As shown in Table S4, the maximum adsorption capacities

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(Qmax, mg/g) of rGOs and magnetic rGOs for 4-n-NP calculated from Langmuir

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model at pH 6.5 and 293 K are 71.10 and 63.96 mg/g, respectively, which are

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significantly higher than those of BPA (58.20 mg/g for rGOs and 48.74 mg/g for

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magnetic rGOs). Comparing to other carbonaceous materials, the adsorption capacity

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of magnetic rGOs for BPA is significantly higher than those of activated carbon (23.5

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mg/g),56 porous carbon (11.4 mg/g),56 carbonaceous materials (31.4 mg/g),57 whereas

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the higher adsorption capacity of CNTs (61.0 mg/g) for BPA is observed.58 This



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phenomenon could be due to the much lower adsorption capacity of the iron oxide on

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magnetic rGOs compared to the graphitic sheet.

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The repeated availability of advanced adsorbents is an important factor for the cost

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reductions in practical application. The repeated adsorption of 4-n-NP and BPA on

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magnetic rGOs is showed in Figure 5A. It is observed that the equilibrium adsorption

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amount of magnetic rGOs for 4-n-NP at C0 = 1.0 mg/L and pH 6.5 reduces from 38.42

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mg/g to 33.45 mg/g, whereas the equilibrium adsorption amount of magnetic rGOs for

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BPA decreases from 29.72 mg/g to 26.40 mg/g after 4 recycling. The slight decline in

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efficiency (< 10 %) indicates that the magnetic rGOs present a good reusability and

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stability. Therefore, the magnetic rGOs can be used as a promising adsorbent to

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remove BPA and 4-n-NP from wastewater.

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FTIR and SEM Analysis. The interaction mechanisms between 4-n-NP/BPA and

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rGOs or magnetic rGOs are demonstrated by FTIR spectra, SEM image after

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adsorption and theoretical calculations. Figure 5B shows the FTIR spectra of

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magnetic rGOs after 4-n-NP and BPA adsorption. After adsorption, there is slight

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difference in the bands of magnetic rGOs at 1167, 1511 and 3444 cm−1, corresponding

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to the C−O stretching vibration, the skeletal vibration of aromatic C=C stretching

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vibration and the O−H stretching vibration, respectively. The many characteristic

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peaks of 4-n-NP and BPA (e.g., 2800−3000 and 500−2000 cm−1) are also observed on

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magnetic rGOs after adsorption, indicating that 4-n-NP/BPA is adsorbed on magnetic

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rGOs. The C=C peak of magnetic rGOs after adsorption shifts from ~1617 to 1625

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cm-1, which could be attributed to the interactions between the benzene rings of


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4-n-NP/BPA and magnetic rGOs. The shifts of the -OH peaks of 4-n-NP (from 3444

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to 3415 cm−1) and BPA (from 3444 to 3428 cm−1) indicate hydrogen bonding plays an

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important role in the adsorption of 4-n-NP/BPA on magnetic rGOs.17 The change in

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morphologies of magnetic rGOs after adsorption are also investigated by SEM images

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(Figure S1E and F). The morphologies of rGOs and magnetic rGOs are changed from

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intrinsic wrinkles and groove surface into relative plat surface after adsorption. As

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shown in Figure 1A, the surface of magnetic rGOs presents the lamella with abundant

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macropores. Therefore, high adsorption performance of rGOs and magnetic rGOs

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could be attributed to the occupation of BPA and 4-n-NP into these groove and

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interstitial region.12,24 The difference in adsorption affinities is also related with the

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physicochemical properties of adsorbates. As shown in Table S1, the value of

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octanol-water distribution coefficients of 4-n-NP (log Kow = 5.76) is higher than that

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of BPA (log Kow = 3.32), indicating that the 4-n-NP presents the stronger

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hydrophobic interactions compared to BPA.59,60

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DFT Calculations. Figure 6 shows the most stable structures of BPA and 4-n-NP

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adsorption on rGOs and GOs. As shown in Figure 6A, the BPA attaches rGOs with

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V-shaped structures at minimum distance of 2.80 Å, and contact angle of BPA slightly

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increases from 109.3º to 112.26 º to maximize π–π stacking. However, 4-n-NP

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attaches the surface of rGOs at a minimum distance of 2.68 Å by rotating its phenol

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ring. As shown in Table 1, the low adsorption energy (Ead) between rGOs and

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BPA/4-n-NP (< 10 kcal/mol) indicates that physisorption is mainly interaction

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mechanism of rGOs and BPA/4-n-NP.30,61 Compared to rGOs + BPA (6.71 kcal/mol),



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the slightly higher Ead value of rGOs + 4-n-NP (9.77 kcal/mol) reveals the higher

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adsorption capacity, which is consistent with the higher maximum adsorption

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mechanism of rGOs for 4-n-NP (71.10 mg/g) and BPA (58.20 mg/g). Figure 6B shows

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the stable structures of BPA and 4-n-NP adsorption on two –OH groups on the basal

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plane of GOs. It has been determined that massive –OH groups are observed on the

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basal plane of GOs.62-64 As shown in Figure 6B, the most stable adsorption structure

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of BPA and GOs can be obtained by combining BPA with two –OH groups of GOs at

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the bond lengths of 2.010 Å and 1.969 Å. The flexibility of the 4-n-NP alkyl chain

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may adjust the molecule to get the best position, allowing better contact not only

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between the π-clouds of the phenol rings and adsorbents, but also the –OH groups

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between the functional groups and the alkyl groups. Therefore, the increased Ead value

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of GOs + 4-n-NP (16.46 kcal/mol) is attributed to the overlapping the phenol ring of

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4-n-NP with two –OH groups on the basal plane of GOs at the bond length of 1.784 Å

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and 2.366 Å, respectively. The Ead values and stable structures of 4-n-NP and BPA

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with two different oxygenated functional groups (such as epoxy, carboxyl groups) at

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the edge and on the plane of GOs were also summarized in Table S5 and Figure S6,

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respectively. As shown in Table S5, the Ead value of GOs + BPA is lower than that of

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GOs + 4-n-NP, which is consistent with the results of rGOs+ BPA and rGOs +4-n-NP.

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Cortes-Arriagada et al.65 also demonstrated that the π-π stacking and hydrogen

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bonding played an important role in the adsorption of BPA on GOs by DFT

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calculations. As summarized in Table 1, the Ead values of 4-n-NP and BPA with two

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–OH groups on the basal plane of GOs are calculated to be 16.46 and 11.85 kcal/mol,


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respectively, which is significantly higher than those of two –O- groups on the basal

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plane of GOs (Table S5). It is demonstrated that –OH groups on the basal plane of

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GOs present the higher chemical reactivity because these –OH groups were easily

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abstracted by adsorbate in aqueous solutions.30,66 The results of FTIR, SEM analysis

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and DFT calculations indicate that the hydrogen bonding, hydrophobic interaction and

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π-π stacking dominate the adsorption of 4-n-NP/BPA on rGOs/magnetic rGOs.

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In summary, magnetic rGOs present the high adsorption capacity for 4-n-NP and BPA,

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indicating that magnetic rGOs can be a promising material to remove EDCs from

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wastewater by using a simple and rapid magnetic separation.

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Acknowledgements

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This research was supported by National Natural Science Foundation of China

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(21207135, 21225730, 91326202 and 91126020), 973 projects from MOST of China

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(2011CB933700), Scientific Research Grant of Hefei Science Center of CAS

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(2015SRG-HSC009;

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Development of Jiangsu Higher Education Institutions, and the Collaborative

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Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions,

325

and MCTL Visiting Fellowship Program of Ocean University of China are

326

acknowledged.

327

Supporting Information Available. Additional characterization of rGOs and

328

magnetic rGOs. More detailed information of DFT calculation, and the parameters of

329

model simulation. This information is available free of charge via the Internet at

330

http://pubs.acs.org.

2015SRG-HSC006),

the

Priority


Academic

Program


Page 16 of 33 16 / 33

331

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526 527


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528

Figure Captions

529

Figure 1. The characterization of rGOs and magnetic rGOs, A and B: SEM and TEM

530

images of magnetic rGOs, respectively; C: XRD patterns; D: FTIR spectra; E: C1s

531

XPS spectra; F: Raman spectra.

532

Figure 2. The adsorption kinetics of BPA (A) and 4-n-NP (B) on rGOs and magnetic

533

rGOs, C0 = 1.0 mg/L, pH = 6.5, I = 0.01mol/L NaCl, m/v = 0.02 g/L, T= 293 K.

534

Figure 3. The effect of pH (A) and ionic strength (B) on 4-n-NP and BPA adsorption

535

onto rGOs and magnetic rGOs, A: C0 = 1.0 mg/L, I = 0.01 mol/L NaCl, m/v = 0.02

536

g/L, T = 293 K; B: C0 = 1.0 mg/L, pH = 6.5, m/v = 0.02 g/L, T = 293 K.

537

Figure 4. The adsorption isotherms of BPA and 4-n-NP on rGOs and magnetic rGOs,

538

A and B: BPA adsorption in the absence and presence of HA, respectively; C and D:

539

4-n-NP adsorption in the absence and presence of HA, respectively, pH = 6.5, I = 0.01

540

mol/L NaCl, m/V = 0.02 g/L, T = 293 K.

541

Figure 5. A: Recycling of magnetic rGOs in the adsorption of BPA and 4-n-NP, C0 =

542

1.0 mg/L, pH = 6.5, I = 0.01 mol/L NaCl, m/V = 0.02 g/L, T = 293 K; B: FTIR

543

spectra of magnetic rGOs after BPA and 4-n-NP adsorption.

544

Figure 6. Optimized geometrical structures of the adsorption of BPA (A) and 4-n-NP

545

(B) on rGOs and GOs.



Page 26 of 33 26 / 33

546

Table 1. The optimized adsorption energies (Ead) of BPA and 4-n-NP on rGOs and

547

GOs

548

EG Hartree /Particle

EBPA/4-n-NP Hartree /Particle

EG-BPA/4-n-NP Hartree /Particle

Ead kcal/mol

rGOs + BPA

-2680.61

-731.48

-3412.10

6.71

rGOs +4-n-NP

-2680.61

-661.02

-3341.64

9.77

GOs + BPA

-2832.13

-731.48

-3563.63

11.85

GOs + 4-n-NP

-2832.13

-661.02

-3493.16

16.46

Samples

549


Page 27 of 33


550 551

Figure 1.

552



Page 28 of 33 28 / 33

553

45

A

B

40

Qe(mg/g)

35 30 25 20 15 10 rG O s M agnetic rG O s

5 0 0 554

10 2 0 3 0 40 50 6 0 7 0 R eactio n tim e (h )

rG O s M agnetic rG O s

0

10 2 0 3 0 40 50 6 0 70 R eactio n tim e (h)

555 556 557

Figure 2

558 559 560 561


Page 29 of 33


562 563 A

45

B

Qe (mg/g)

40 35 30 BPA-rGOs BPA-magnetic-rGOs 4-n-NP-rGOs 4-n-NP-magnetic-rGOs

BPA- rGOs BPA- magnetic-rGOs 4-n-NP-rGOs 4-n-NP-magnetic-rGOs

25 20 3

4

5

6

7

pH

8

9

10 11

0.00

0.02

0.04

564 565

0.06

NaCl (mol/L)

Figure 3.

566 567 568 569 570 571 572 573 574 575 576 577 578


0.08

0.10


Page 30 of 33 30 / 33

579 580 70

581

B

60 50

Qe (mg/g)

582 583

A

584

40 30

10

585

0

70

586

BPA-rGOs-HA BPA-magnetic rGOs-HA Langmuir model Freundlich model

BPA-rGOs BPA-magnetic rGOs Langmuir model Freundlich model

20

C

D

60

587 588 589

Qe (mg/g)

50 40 30 20

590 591

10

4-n-NP-rGOs-HA 4-n-NP-magnetic rGOs-HA Langmuir model Freundlich model

4-n-NP-rGOs 4-n-NP-magnetic rGOs Langmuir model Freundlich model

0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Ce (mg/L)

Ce (mg/L) 592 593 594 595

Figure 4

596


Page 31 of 33


597 598

40

A

4-n-NP BPA

B 4-n-NP

36 32

Qe (mg/g)

28

Magnetic rGO after 4-n-NP adsorption

24 20

BPA

16 12

Magnetic rGO after BPA adsorption

8

Magnetic rGO

4 0 1 599

2

Cycle

3

4

800

1200

600 601 602

1600 2800

-1

Wavenumber (cm )

Figure 5

603 604 605 606 607 608 609 610


3200


Page 32 of 33 32 / 33

611

612 613

Figure 6


Page 33 of 33


614

For Table of Contents Only

615 616 617


Nonylphenol and Bisphenol-A on Magnetic ... - ACS Publications

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