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

Jul 10, 2015 - Adsorption of phenanthrene and pyrene by biochar produced from the excess sludge: experimental studies and theoretical analysis. W. Guo...
0 downloads 12 Views 2MB Size
Page 1 of 33

Environmental Science & Technology 1 / 33

1

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

2

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

3 4

Wang1,4,5*

5

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

6 7

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

8 9

3.

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

10

4. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher

11

Education Institutions and School for Radiological and Interdisciplinary Sciences,

12

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

13 14

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

15

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

16

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

17

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

18

ABSTRACT

19

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

20

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

21

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

22

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 2 of 33 2 / 33

23

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

24

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

25

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

26

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

27

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

28

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

29

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

30

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

31

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

32

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

33

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

34

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

35

endocrine-disrupting chemicals in environmental cleanup.

36

INTRODUCTION

37

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

38

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

39

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

40

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

41

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

42

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

43

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

44

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

ACS Paragon Plus Environment

Page 3 of 33

Environmental Science & Technology 3 / 33

45

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

46

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

47

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

48

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

49

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

50

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

51

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

52

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

53

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

54

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

55

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

56

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

57

are available.22-24

58

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

59

extensively investigated to remove organic contaminants in environmental pollution

60

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

61

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

62

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

63

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

64

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

65

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

66

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 33 4 / 33

67

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

68

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

69

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

70

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

71

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

72

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

73

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

74

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

75

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

76

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

77

of the fate and transport of EDCs in aquatic environments.

78

EXPERIMENTAL SECTION

79

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

80

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

81

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

82

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

83

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

84

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

85

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

86

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

87

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

88

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

ACS Paragon Plus Environment

Page 5 of 33

Environmental Science & Technology 5 / 33

89

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

90

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

91

Sinopharm Chemical Reagent Co., Ltd.

92

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

93

modified Hummers method37 and by hydrazine hydrate reduction of GOs under

94

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

95

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

96

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

97

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

98

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

99

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

100

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

101

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

102

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

103

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

104

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

105

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

106

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

107

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

108

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

109

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

110

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 6 of 33 6 / 33

111

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

112

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

113

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

114

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

115

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

116

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

117

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

118

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

119

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

120

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

121

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

122

adsorption equilibrium were separated from liquid phases by using a permanent

123

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

124

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

125

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

126

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

127

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

128

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

129

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

130

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

131

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

132

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

ACS Paragon Plus Environment

Page 7 of 33

Environmental Science & Technology 7 / 33

133

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

134

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

135

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

136

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

137

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

138

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

139

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

140

method,41 respectively.

141

RESULTS AND DISCUSSION

142

Characterization. The morphologies of magnetic rGOs are characterized by SEM

143

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

144

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

145

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

146

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

147

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

148

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

149

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

150

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

151

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

152

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

153

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

154

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 8 of 33 8 / 33

155

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

156

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

157

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

158

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

159

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

160

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

161

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

162

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

163

consistent with previous study.45

164

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

165

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

166

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

167

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

168

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

169

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

170

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

171

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

172

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

173

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

174

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

175

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

176

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

ACS Paragon Plus Environment

Page 9 of 33

Environmental Science & Technology 9 / 33

177

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

178

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

179

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

180

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

181

kinetics results indicate that rGOs and magnetic rGOs possess high adsorption

182

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

183

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

184

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

185

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

186

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

187

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

188

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

189

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

190

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

191

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

192

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

193

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

194

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

195

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

196

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

197

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

198

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 10 of 33 10 / 33

199

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

200

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

201

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

202

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

203

higher pH values.

204

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

205

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

206

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

207

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

208

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

209

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

210

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

211

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

212

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

213

the electrostatic attraction.

214

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

215

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

216

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

217

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

218

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

219

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

220

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

ACS Paragon Plus Environment

Page 11 of 33

Environmental Science & Technology 11 / 33

221

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

222

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

223

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

224

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

225

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

226

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

227

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

228

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

229

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

230

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

231

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

232

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

233

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

234

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

235

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

236

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

237

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

238

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

239

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

240

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

241

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

242

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 12 of 33 12 / 33

243

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

244

magnetic rGOs compared to the graphitic sheet.

245

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

246

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

247

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

248

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

249

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

250

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

251

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

252

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

253

remove BPA and 4-n-NP from wastewater.

254

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

255

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

256

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

257

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

258

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

259

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

260

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

261

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

262

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

263

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

264

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

ACS Paragon Plus Environment

Page 13 of 33

Environmental Science & Technology 13 / 33

265

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

266

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

267

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

268

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

269

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

270

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

271

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

272

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

273

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

274

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

275

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

276

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

277

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

278

hydrophobic interactions compared to BPA.59,60

279

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

280

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

281

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

282

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

283

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

284

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

285

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

286

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

ACS Paragon Plus Environment

Environmental Science & Technology

Page 14 of 33 14 / 33

287

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

288

adsorption capacity, which is consistent with the higher maximum adsorption

289

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

290

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

291

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

292

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

293

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

294

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

295

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

296

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

297

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

298

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

299

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

300

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

301

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

302

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

303

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

304

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

305

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

306

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

307

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

308

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

ACS Paragon Plus Environment

Page 15 of 33

Environmental Science & Technology 15 / 33

309

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

310

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

311

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

312

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

313

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

314

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

315

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

316

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

317

wastewater by using a simple and rapid magnetic separation.

318

Acknowledgements

319

This research was supported by National Natural Science Foundation of China

320

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

321

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

322

(2015SRG-HSC009;

323

Development of Jiangsu Higher Education Institutions, and the Collaborative

324

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

ACS Paragon Plus Environment

Academic

Program

Environmental Science & Technology

Page 16 of 33 16 / 33

331

REFERENCES

332

(1) Sharma, V.K.; Anquandah, G.A.K.; Yngard, R.A.; Kim, H.; Fekete, J.; Bouzek, K.;

333

Ray, A.K.; Golovko, D. Nonylphenol, octylphenol, and bisphenol-A in the aquatic

334

environment: A review on occurrence, fate, and treatment. J. Environ. Sci. Health

335

Part A 2009, 44, 423-442.

336

(2) Ferrara, F.; Ademolllo, N.; Delise, M.; Fabietti, F.; Funari, E.; Alkylphenols and

337

their ethoxylates in seafood from the Tyrrhenian Sea. Chemosphere 2008, 72,

338

1279-1285.

339 340 341 342

(3) Vandenberg, L.N.; Hauser, R.; Marcus, M.; Olea, N.; Welshons, W.V.; Human exposure to bisphenol A. Reprod. Toxicol. 2007, 24, 139–177. (4) Mielke, H.; Gundert-Remy, U.; Bisphenol A levels in blood depend on age and exposure. Toxicol. Lett. 2009, 190, 32–40.

343

(5) Muñoz-de-Toro, M.; Markey, C.M.; Wadia, P.R.; Luque, E.H.; Rubin, B.S.;

344

Sonnenschein, C.; Soto, A.M. Perinatal exposure to bisphenol A alters

345

peripubertal mammary gland development in mice. Endocrinology 2005, 146,

346

4138–4147.

347

(6) Sugiura-Ogasawara, M.; Ozaki, Y.; S. S.; Makino, T.; Suzumori, K. Exposure to

348

bisphenol A is associated with recurrent miscarriage. Hum. Reprod. 2005, 20,

349

2325–2329.

350

(7) Kandaraki, E.; Chatzigeorgiou, A.; Livadas, S.; Palioura, E.; Economou, F.;

351

Koutsilieris, M.; Palimeri, S.; Panidis, D.; Diamanti-Kandarakis, E. Endocrine

352

disruptors and polycystic ovary syndrome(PCOS): elevated serum levels of

353

bisphenol A in women with PCOS. J. Clin. Endocrinol. Metab. 2011, 96,

ACS Paragon Plus Environment

Page 17 of 33

Environmental Science & Technology 17 / 33

354

480–484.

355

(8) Bae, S.; Kim, J.H.; Lim, Y.H.; Park, H.Y.; Hong, Y.C. Associations of bisphenol

356

A exposure with heart rate variability and blood pressure. J. Hypertens. 2012, 60,

357

786–793.

358

(9) Soares, A.; Guieysse, B.; Jefferson, B.; Cartmell, E.; Lester, J.N. Nonylphenol in

359

the environment: A critical review on occurrence, fate, toxicity and treatment in

360

wastewaters. Environ. Int. 2008, 34, 1033-1049.

361

(10) Luo, X.B.; Deng, F.; Min, L.J.; Luo, S.L.; Guo, B.; Zeng, G.S.; Au, C.T. Facile

362

one-step synthesis of inorganic-framework molecularly imprinted TiO2/WO3

363

nanocomposite and its molecular recognitive photocatalytic degradation of target

364

contaminant. Environ. Sci. Technol. 2013, 47, 7404-7412.

365 366

(11) Zhang, Z.B.; Hu, J.Y. Selective removal of estrogenic compounds by molecular imprinted polymer (MIP). Water. Res. 2008, 42, 4101-4108.

367

(12) Pan, B.; Lin, D.H.; Mashayekhi, H.; Xing, B.S. Adsorption and hysteresis of

368

bisphenol A and 17 α-ethinyl estradiol on carbon nanomaterials. Environ. Sci.

369

Technol. 2008, 42, 5480-5485.

370

(13) Li, G.Y.; Zu, L.; Wong, P.K.; Hui, X.P.; Lu, Y.; Xiong, J.K.; An, T.C.

371

Biodegradation and detoxification of bisphenol A with one newly-isolated strain

372

Bacillus sp GZB: Kinetics, mechanism and estrogenic transition. Bioresour.

373

Technol. 2012, 114, 224-230.

374

(14) Liu, G.F.; Ma, J.; Li, X.C.; Qin, Q.D. Adsorption of bisphenol A from aqueous

375

solution onto activated carbons with different modification treatments. J. Hazard.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 18 of 33 18 / 33

376 377

Mater. 2009, 164, 1275-1280. (15) Yu, Z.; Peldszus, S.; Huck, P. M. Adsorption characteristics of selected

378

pharmaceuticals

and

an

endocrine

disrupting

compound-Naproxen,

379

carbamazepine and nonylphenol -on activated carbon. Water Res. 2008, 42,

380

2873-2882.

381

(16) Wang, B.Y.; Chen, W.; Fu, H.Y.; Qu, X.L.; Zheng, S.R.; Xu, Z.Y.; Zhu, D.Q.

382

Comparison of adsorption isotherms of single-ringed compounds between carbon

383

nanomaterials and porous carbonaceous materials over six-order-of-magnitude

384

concentration range. Carbon 2014, 79, 203-212.

385

(17) Liu, F.F.; Zhao, J.; Wang, S.G..; Du, P.; Xing, B.S. Effects of solution chemistry

386

on adsorption of selected pharmaceuticals and personal care products (PPCPs) by

387

graphenes and carbon nanotubes. Environ. Sci. Technol. 2014, 48, 13197-13206.

388 389

(18) Wang, F.; Yao, J.; Sun, K.; Xing, B.S. Adsorption of dialkyl phthalate esters on carbon nanotubes. Environ. Sci. Technol. 2010, 44, 6985-6991.

390

(19) Yang, K. J.; Wang, J.; Chen, B. L. Facile fabrication of stable monolayer and

391

few-layer graphene nanosheets as superior sorbents for persistent aromatic

392

pollutant management in water. J. Mater. Chem. A 2014, 2, 18219-18224.

393

(20) Shen, Y.; Fang, Q. L.; Chen, B. L. Environmental applications of three-

394

dimensional grphene-based macrostructures: adsorption, transformation, and

395

detection. Environ. Sci. Technol. 2014, 49, 67-84.

396

(21) Chen, X. X.; Chen, B. L. Macroscopic and spectroscopic investigations of the

397

adsorption of nitroaromatic compounds on graphene oxide, reduced graphene

ACS Paragon Plus Environment

Page 19 of 33

Environmental Science & Technology 19 / 33

398

oxide, and graphene nanosheets. Environ. Sci. Technol. 2015, 49, 6181-6189.

399

(22) Zhang, Y.H.; Tang, Y.L.; Li, S.Y.; Yu, S.L. Sorption and removal of

400

tetrabromobisphenol A from solution by graphene oxide. Chem. Eng. J. 2013, 222,

401

94-100.

402 403

(23) Xu, J.; Wang, L.; Zhu, Y.F. Decontamination of bisphenol A from aqueous solution by graphene adsorption. Langmuir 2012, 28, 8418-8425.

404

(24) Zhang, Y.X.; Cheng, Y.X.; Chen, N.N.; Zhou, Y.Y.; Li, B.Y.; Gu, W.; Shi, X.H.;

405

Xian, Y.Z. Recyclable removal of bisphenol A from aqueous solution by reduced

406

graphene oxide-magnetic nanoparticles: Adsorption and desorption. J. Colloid

407

Interface Sci. 2014, 421, 85-92.

408

(25) Cai, Y.Q.; Jiang, G.B.; Liu, J.F.; Zhou, Q.X. Multiwalled carbon nanotubes as a

409

solid-phase extraction adsorbent for the determination of bisphenol A, 4-n-

410

nonylphenol, and 4-tert-octylphenol. Anal. Chem. 2003, 75, 2517-2521.

411

(26) Sun, Y.B.; Wang, Q.; Chen, C.L.; Tan, X.L.; Wang, X.K. Interaction between

412

Eu(III) and Graphene oxide nanosheets investigated by batch and extended X-ray

413

absorption fine structure spectroscopy and by modeling techniques. Environ. Sci.

414

Technol. 2012, 46, 6020-6027.

415

(27) Ji, L.L.; Chen, W.; Xu, Z. Y.; Zheng, S.R.; Zhu, D.Q. Graphene nanosheets and

416

graphite oxide as promising adsorbents for removal of organic contaminants from

417

aquesous solution. J. Environ. Qual. 2013, 42, 191-198.

418

(28) Sun, Y.B.; Shao, D.D.; Chen, C.L.; Yang, S.B.; Wang, X.K. Highly Efficient

419

Enrichment of Radionuclides on Graphene Oxide Supported Polyaniline. Environ.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 20 of 33 20 / 33

420

Sci. Technol. 2013, 47, 9904-9910.

421

(29) Wang, J.; Chen, Z.M.; Chen, B.L. Adsorption of polycyclic aromatic

422

hydrocarbons by graphene and graphene oxide nanosheets. Environ. Sci. Technol.

423

2014, 48, 4817-4825.

424

(30) Sun, Y.B.; Yang, S.B.; Chen, Y.; Ding, C.C.; Cheng, W.C.; Wang, X.K.

425

Adsorption and desorption of U(VI) on functionalized graphene oxides: a

426

combined experimental and theoretical study. Environ. Sci. Technol. 2015, 49,

427

4255-4262.

428

(31) Huang, J.; Chang, Q.; Ding, Y. B.; Han, X. Y.; Tang, H. Q. Catalytic oxidative

429

removal of 2,4-dichlorophenol by simultaneous use of horseradish peroxidase and

430

graphene oxide/Fe3O4 as catalyst. Chem. Eng. J. 2014, 254, 434-442.

431

(32) Wang, X. B.; Huang, S. S.; Zhu, L. H.; Tian, X. L.; Li, S. H.; Tang, H. Q.

432

Correlation between the adsorption ability and reduction degree of graphene

433

oxide and tuning of adsorption of phenolic compounds. Carbon 2014, 69,

434

101-112.

435

(33) Zhao, J.; Wang, Z. Y.; White, J. C.; Xing, B. S. Graphene in the aquatic

436

environment: Adsorption, dispersion, toxicity and transformation. Environ. Sci.

437

Technol. 2014, 48, 9995-10009.

438

(34) Liu, M.C.; Chen, C.L.; Hu, J.; Wu, X.L.; Wang, X.K. Synthesis of magnetite/

439

graphene oxide composite and application for cobalt(II) removal. J. Phys. Chem.

440

C 2011, 115, 25234-25240.

441

(35) Yang, X.; Chen, C.L.; Li, J.X.; Zhao, G.X.; Ren, X.M.; Wang, X.K. Graphene

ACS Paragon Plus Environment

Page 21 of 33

Environmental Science & Technology 21 / 33

442

oxide-iron oxide and reduced graphene oxide-iron oxide hybrid materials for the

443

removal of organic and inorganic pollutants. RSC Adv. 2012, 2, 8821-8826.

444

(36) Luo, Y.B.; Shi, Z.G.; Gao, Q.A.; Feng, Y.Q. Magnetic retrieval of graphene:

445

extraction of sulfonamide antibiotics from environmental water samples. J.

446

Chromatogr. A 2011, 1218, 1353–1358.

447 448

(37) Hummers, W.S.; Offeman, R.E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339.

449

(38) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.: Kleinhammes, A.; Jia,

450

Y. Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of grapheme-based

451

nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45,

452

1558-1565.

453 454

(39) Becke, A.D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993. 98, 5648-5652.

455

(40) Grimme, S. Accurate description of van der waals complexes by density

456

functional theory including empirical corrections. J. Comput. Chem. 2004, 25,

457

1463-1473.

458 459 460 461 462 463

(41) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum mechanical continuum solvation models. Chem. Rev. 2005, 105, 2999-3093. (42) Meyer, J. C.; Geim, A. K.; Katsnelson, M. I.; Novoselov, K. S.;Booth, T. J.; Roth, S. The structure of suspended graphene sheets. Nature 2007, 446, 60−63. (43) Fasolino, A.; Los, J. H.; Katsnelson, M. I. Intrinsic ripples in graphene. Nat. Mater. 2007, 6, 858−861.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 22 of 33 22 / 33

464

(44) Sun, Y.B.; Yang, S.B.; Zhao, G.X.; Wang, Q.; Wang, X.K. Adsorption of

465

polycyclic aromatic hydrocarbons on graphene oxides and reduced graphene

466

oxides. Chem. Asian J. 2013, 8, 2755-2761.

467

(45) Yang, X.Y.; Zhang, X.Y.; Ma, Y.F.; Huang, Y.; Wang, Y.S.; Chen, Y.S.

468

Superparamagnetic graphene oxide-Fe3O4 nanoparticles hybrid for controlled

469

targeted drug carriers. J. Mater. Chem. 2009, 19, 2710-2714.

470

(46) Gao, H. C.; Xiao, F.; Ching, C. B.; Duan, H. W. One-Step electrochemical

471

synthesis of PtNi nanoparticle-graphene nanocomposites for nonenzymatic

472

amperometric glucose detection. ACS Appl. Mater. Interfaces 2011, 3,

473

3049-3057.

474

(47) Wang, T.S.; Liu, Z.H.; Lu, M.M.; Wen, B.; Ouyang, Q.Y.; Chen, Y.J.; Zhu, C.L.;

475

Gao, P.; Li, C.Y.; Cao, M.S.; Qi, L.H. Graphene-Fe3O4 nanohybrids: Synthesis

476

and excellent electromagnetic absorption properties. J. Appl. Phys. 2013, 113,

477

024314.

478 479 480 481

(48) Lagergren, S. Zur theorie der sogenannten adsorption geloster stoffe. Kungl. Svenska Vetenskapsakad. Handl. 1898, 24, 1–39. (49) Ho, Y.S.; McKay, G. Kinetic models for the sorption of dye from aqueous solution by wood. Proc. Saf. Environ. Prot. 1998, 76, 183–191.

482

(50) Bautisat-Toledo, I.; Ferro-Garcia, M. A.; Rivera-Utrilla, J.; Moreno-Castilla, C.;

483

Fernadez, F. J. V. Bisphenol A removal from water by activated carbon: effects of

484

carbon characteristics and solution chemistry. Environ. Sci. Technol. 2005, 39,

485

6246-6250.

ACS Paragon Plus Environment

Page 23 of 33

Environmental Science & Technology 23 / 33

486 487

(51) Yan, W. L.; Bai, R. B. Adsorption of lead and humic acid on chitosan hydrogel beads. Water Res. 2005, 39, 688-698.

488

(52) Sun, Y. B.; Yang, S. T.; Sheng, G. D.; Guo, A. Q.; Wang, X. K. The removal of

489

U(VI) from aqueous solution by oxidized multiwalled carbon nanotubes. J.

490

Environ. Radioact. 2012, 105, 40-47.

491

(53) Wang, X.L.; Lu, J.L.; Xing, B.S. Sorption of organic contaminants by carbon

492

nanotubes: Influence of adsorbed organic matter. Environ. Sci. Technol. 2008, 42,

493

3207-3212.

494 495 496 497

(54) Langmuir, I. The adsorption of gases on plane surface of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361–1403. (55) Freundlich, H. M. F. Uber die adsorption in Losungen. J. Phys. Chem. 1906, 57, 385–470.

498

(56) Asada, T.; Oikawa, K.; Kawata, K.; Ishihara, S.; Iyobe, T.; Yamada, A. Study of

499

removal effect of bisphenol A and beta-estradiol by porous carbon. J. Health Sci.

500

2004, 50, 588−593.

501

(57) Nakanishi, A.; Tamai, M.; Kawasaki, N.; Nakamura, T.; Tanada, S. Adsorption

502

characteristics of bisphenol A onto carbonaceous materials produced from wood

503

chips as organic waste. J. Colloid. Interface Sci. 2002, 252, 393-396.

504 505

(58) Kuo, C. Y. Comparison with as-grown and microwave modified carbon nanotubes to removal aqueous bisphenol A. Desalination 2009, 249, 976-982.

506

(59) Sun, K.; Gao, B.; Zhang, Z.Y.; Zhang, G.X.; Liu, X.T.; Zhao, Y.; Xing, B.S.

507

Sorption of endocrine disrupting chemicals by condensed organic matter in soils

ACS Paragon Plus Environment

Environmental Science & Technology

Page 24 of 33 24 / 33

508 509 510

and sediments. Chemosphere 2010, 80, 709-715. (60) Ying, G.G.; Kookana, R.S. Sorption and degradation of estrogen-like-endocrine disrupting chemicals in soil. Environ. Toxicol. Chem. 2005, 24, 2640-2645.

511

(61) Wu, Q. Y.; Lan, J. H.; Wang, C. Z.; Xiao, C. L.; Zhao, Y. L.; Wei, Y. Z.; Chai, Z.

512

F.; Shi, W. Q. Understanding the bonding nature of uranyl ion and functionalized

513

graphene: A theoretical study. J. Phys. Chem. A 2014, 118, 2149−2158.

514 515 516 517 518 519

(62) Lerf, A.; He, H. Y.; Forster, M.; Klinowski, J. Structure of graphite oxide revisited. J. Phys. Chem. B 1998, 102, 4477−4482. (63) Eda, G.; Chhowalla, M. Chemically derived graphene oxide: towards large-area thin-film electronics and optoelectronics. Adv. Mater. 2010, 22, 2392−2415. (64) Chen, D.; Feng, H.; Li, J. Graphene oxide: preparation, functionalization, and electrochemical applications. Chem. Rev. 2012, 112, 6027−6053.

520

(65) Cortes-Arriagada, D.; Sanhueza, L.; Santander-Nelli, M. Modeling the

521

physisorption of bisphenol A on graphene and graphene oxide. J. Mol. Model.

522

2013, 19, 3569-3580.

523

(66) Yang, S.; Chen, C.; Chen, Y.; Wang, D.; Wang, X. Competitive adsorption of

524

Pb(II), Ni(II) and Sr(II) ions on graphene oxides: A combined experimental and

525

theoretical study. ChemPlusChem 2015, 80, 480−484.

526 527

ACS Paragon Plus Environment

Page 25 of 33

Environmental Science & Technology 25 / 33

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.

ACS Paragon Plus Environment

Environmental Science & Technology

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

ACS Paragon Plus Environment

Page 27 of 33

Environmental Science & Technology 27 / 33

550 551

Figure 1.

552

ACS Paragon Plus Environment

Environmental Science & Technology

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

ACS Paragon Plus Environment

Page 29 of 33

Environmental Science & Technology 29 / 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

ACS Paragon Plus Environment

0.08

0.10

Environmental Science & Technology

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

ACS Paragon Plus Environment

Page 31 of 33

Environmental Science & Technology 31 / 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

ACS Paragon Plus Environment

3200

Environmental Science & Technology

Page 32 of 33 32 / 33

611

612 613

Figure 6

ACS Paragon Plus Environment

Page 33 of 33

Environmental Science & Technology 33 / 33

614

For Table of Contents Only

615 616 617

ACS Paragon Plus Environment