Macroscopic, Spectroscopic, and Theoretical Investigation for the

Subscriber access provided by University of Newcastle, Australia

Article

Macroscopic, spectroscopic and theoretical investigation for the interaction of phenol and naphthol on reduced graphene oxide Shujun Yu, Xiangxue Wang, Wen Yao, Jian Wang, Yongfei Ji, Yuejie Ai, Ahmed Alsaedi, Tasawar Hayat, and Xiangke Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b06259 • Publication Date (Web): 28 Feb 2017 Downloaded from http://pubs.acs.org on February 28, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

Environmental Science & Technology

1

Macroscopic, spectroscopic and theoretical investigation for the interaction of

2

phenol and naphthol on reduced graphene oxide

3

Shujun Yu1, Xiangxue Wang1, Wen Yao1, Jian Wang1, Yongfei Ji2, Yuejie Ai1,2*,

4

Ahmed Alsaedi3, Tasawar Hayat3, Xiangke Wang1,3*

5

1. School of Environment and Chemical Engineering, North China Electric Power

6

University, Beijing, 102206, P.R. China

7

2. Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of

8

Technology, Roslagstullsbacken 15, 10691 Stockholm, Sweden

9

3. NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah

10

21589, Saudi Arabia

11

ABSTRACT

12

Interaction of phenol and naphthol with reduced graphene oxide (rGO), and their

13

competitive behavior on rGO were examined by batch experiments, spectroscopic

14

analysis and theoretical calculations. The batch sorption showed that the removal

15

percentage of phenol or naphthol on rGO in bi-solute systems was significantly lower

16

than those of phenol or naphthol in single-solute systems. However, the overall

17

sorption capacity of rGO in bi-solute system was higher than single-solute system,

18

indicating that the rGO was a very suitable material for the simultaneous elimination

19

of organic pollutants from aqueous solutions. The interaction mechanism was mainly

20

π-π interactions and hydrogen bonds, which was evidenced by FTIR, Raman and

1

ACS Paragon Plus Environment


21

theoretical calculation. FTIR and Raman showed that a blue shift of C=C and -OH

22

stretching modes and the enhanced intensity ratios of ID/IG after phenols sorption. The

23

theoretical calculation indicated that the total hydrogen bond numbers, diffusion

24

constant and solvent accessible surface area of naphthol were higher than those of

25

phenol, indicating higher sorption affinity of rGO for naphthol as compared to phenol.

26

These findings were valuable for elucidating the interaction mechanisms between

27

phenols and graphene-based materials, and provided an essential start in simultaneous

28

removal of organics from wastewater.

29

INTRODUCTION

30

Water is one of the most essential and important components on the earth for all living

31

beings.1 However, water quality is deteriorating continuously owning to the rapid

32

growth of civilization, industrialization, population, and other environmental

33

problems.2-4 Many organic pollutants such as dyes, pesticides, phenols, fertilizers,

34

plasticizers, oils, greases, pharmaceuticals, etc. have been found in different water

35

resources.5,6 Especially, phenols have been listed as priority pollutant by most national

36

environmental protection agencies and most of them are classified as the hazardous

37

pollutants because of their potential risk against human health at low concentrations.7

38

The phenols could accumulate through the food chain and at last enter into the human

39

body and thereby threat the human health and are dangerous to the environment.

40

Thereby, the elimination of organic pollutants from the contaminated water is critical

41

to improve the disease-free health of our society.

42

Sorption is one of the most widely used technologies for the removal of organic 2


Page 2 of 32

Page 3 of 32


43

pollutants from wastewater because of its simple operation, low cost, high efficiency

44

and can be applied in large scale in real applications.8-11 The most popular and widely

45

used adsorbent material was activated carbon and clay-based materials.12-16 Altenor et

46

al.12 utilized vetiver roots to prepared activated carbon and used as adsorbent in

47

wastewater treatment, the maximum sorption capacity was 408 mg/g and 82.32 mg/g

48

for methylene blue and phenol, respectively. Alkaram et al.15 reported that the

49

maximum removal capacity of hexadecyltrimethylammonium bromide-bentonite for

50

phenol was 25.57 mg/g at 25 °C and pH 10.0. Radian and Mishael16 discovered the

51

elevated removal of pyrene to polycation-montmorillonite in the existence of humic

52

substances, which was described to the sorption of pyrene-HA complexes. However,

53

the applications of these materials were restricted because of their low removal

54

capacities or efficiencies.

55

Graphene is the two-dimensional monolayer of sp2 hybridized carbon atoms, which

56

are packed in the hexagonal honeycomb lattice.17 The flat π networks, defects,

57

wrinkles and the oxygen-containing functional groups at the edges and surfaces of

58

graphene nanosheets are valuable for the high sorption of pollutants.18,19 Numerous

59

studies revealed that graphene was superior adsorbent for the removal of organic

60

chemicals in aqueous solutions because of its large and hydrophobic surface

61

area.17,20,21 Shen and Chen22 revealed that the sulfonated graphene was effective

62

adsorbent for phenanthrene (400 mg/g) and methylene blue (906 mg/g). Wang et al.23

63

reported that nitrogen-doped reduced graphene oxide (N-rGO) had high sorption

64

capacity toward bisphenol A (356 mg/g) and bisphenol F (286 mg/g) mainly due to 3



Page 4 of 32

65

π-π interactions. In addition, other high removal capacities for naphthalene,

66

nitrobenzene and p-nitrotoluene have also been reported.17,24 However, only

67

single-solute sorption behavior was investigated in these studies, which was not

68

meaningful for predicting pollutant removal in real environments since co-existence

69

of organic pollutants is much more common.

70

Co-occurrence of multiple organic contaminants in natural environments is

71

commonplace and influences the removal of individual compounds via competitive or

72

cooperative

73

2,4-dichlorophenol and 4-chloroaniline was suppressed by nonpolar naphthalene on

74

multiwalled carbon nanotubes (MWCNTs). Ren et al.26 found the competitive

75

sorption between rhodamine 6G and dopamine onto GO because of the limited

76

sorption active sites. The synergistic effect was reported between methyl blue (MB)

77

and congo red (CR), which promoted the efficient removal of CR on MnFe2O4 and

78

inhibited MB sorption.29 However, few studies have concerned the competitive

79

sorption of organic contaminants onto graphene-based materials.10,26,30 To the best of

80

our knowledge, a comprehensive experiment, spectral and theoretical study on the

81

interaction between aromatic compound and graphene is largely scarce, which is

82

crucial to understand the underlying interaction mechanism and for simultaneous

83

removal of organic pollutants from aqueous solutions.

84

Herein, the interaction of phenol and naphthol with rGO was investigated from

85

experiments, spectroscopy analysis and theoretical calculations for the first time.

86

Phenol and naphthol were selected as typical phenols in the natural environment. The

effects.25-28

Yang

et

al.27

observed

that

4


sorption

of

polar

Page 5 of 32


87

major goals of this research were: (1) to investigate the influence of solution pH,

88

contact time and temperature on the individual sorption process of phenol and

89

naphthol onto rGO from aqueous solutions, (2) to identify the mutual effects of the

90

pollutants in the binary systems, and (3) to derive the interaction mechanism of the

91

phenols with rGO by using the spectroscopic methods (FTIR and Raman) and

92

theoretical calculations. The contents are important to understand the physicochemical

93

behaviour of phenols in the natural environment and for the application of rGO in

94

environmental pollution cleanup.

95

EXPERIMENTAL

96

Materials. The rGO was synthesized by reducing GO according to the previous

97

study.31 More detailed processes on the preparation of GO and rGO were supplied in

98

Supporting Information (SI). The flake graphite (99.95% purity, 48 µm) was obtained

99

from Qingdao Tianhe graphite Company (China). The phenol (≥ 99.5% purity) and

100

naphthol (≥ 99.0% purity) were purchased from Sigma-Aldrich. All other reagents

101

were purchased in analytical grade and used in the experiments without further

102

purification.

103

Characterization. The rGO was characterized by using Fourier-transform infrared

104

spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM),

105

and X-ray photoelectron spectroscopy (XPS). The TEM image was employed on the

106

scanning transmission electron microscope (JEM-2000VF). The XPS spectrum was

107

performed by an ESCALAB 250 Xi XPS with Al Kα radiation. The FTIR spectrum

108

was performed by a Nicolet Magana-IR 750 spectrophotometer over a range from 5



Page 6 of 32

109

4000 to 400 cm-1 using a KBr disc technique. The Raman spectrum was recorded with

110

a Renishew inVia Raman spectrometer (Renishaw) at 532 nm. The potentiometric

111

acid-base titrations

112

computer-controlled automatic titration system (DL50 Automatic Titrator, Mettler

113

Toledo) in 0.01 mol/L NaClO4 as the background electrolyte.

114

Experimental processes for the removal of phenol and naphthol. The sorption

115

experiments of phenol and naphthol on rGO were performed under ambient

116

conditions by using batch technique. Quantitative adsorbent (rGO suspension, 0.1

117

g/L), background solution (NaClO4 solution, 0.01 mol/L) and adsorbate (phenol or

118

naphthol solution, 25 mg/L) were added into the brown glass vials, which were

119

equipped with the polytetrafluoroethylene-lined screw caps. The pH was measured

120

with a digital pH-meter (PHS-3C) by adding negligible amounts of 0.01-1.0 mol/L

121

HClO4 or NaOH solutions. HClO4 and NaOH would not affect phenol or naphthol

122

sorption on rGO with varied pH. The pH of the solution was kept below 0.1 before

123

and after sorption. For the sorption isotherms of phenols, the temperatures were

124

controlled to 298 K, 313 K and 328 K. The competitive sorption of phenol and

125

naphthol on rGO was also carried out at the same level of phenols concentration at

126

298 K. After the vials were shaken for 48 hours to ensure the sorption equilibrium, the

127

solid was separated from the liquid phase by centrifugation at 5595 g for 30 min. The

128

concentration of phenol and/or naphthol was measured by high performance liquid

129

chromatography (HPLC). The blank experiments (without rGO) were carried out

130

under the same conditions to eliminate the mass loss during the reaction processes.

were conducted under argon

gas

6


condition

using a

Page 7 of 32


131

More details on the analysis were supplied in SI. All experimental data were the

132

average of duplicate determinations, and the relative errors were about 5%.

133

Data

134

pseudo-second-order models, which were given as follows32,33:

135

ln (qe − qt ) = lnqe − k1t

(1)

136

t 1 1 = + t 2 qt k 2 q e qe

(2)

137

where qt (mmol/g) was the amount of adsorbed phenol and/or naphthol at time t (h),

138

qe (mmol/g) was the amount of adsorbed phenol and/or naphthol after reacted

139

completely, k1 (1/h) and k2 (mmol/(g·h)) were the rate constant of pseudo-first-order

140

and pseudo-second-order sorption, respectively.

141

The Langmuir34 and Freundlich35 models (eq. 3-4) were used to fit the experimental

142

isotherm data. qe =

143

analysis.

The

kinetic

data

were

fitted

by

bqmaxCe 1 + bCe

pseudo-first-order

and

(3)

144

q e = K F C en

145

where Ce (mmol/L) was the final concentration of phenols in aqueous solutions after

146

sorption equilibration, qe (mmol/g) was the amount of phenols adsorbed on rGO, qmax

147

(mmol/g) was the Langmuir constant, indicated the maximum monolayer sorption

148

capacity, and b (L/mol) was a constant that associated with the sorption energy, KF

149

(mmol1-n Ln/g) was the Freundlich constant when the equilibrium concentration of

150

phenols reach to 1, and n represented the sorption intensity.

151

Theoretical calculations. The geometric optimization, sorption energies and

(4)

7



152

molecular dynamics (MD) calculations for rGO sorption systems were performed by

153

Vienna ab-initio simulation package (VASP) (version5.3.5).36 The density functional

154

theory (DFT) employing projector augmented wave (PAW) method with the

155

Perdew-Burke-Ernzerhof (PBE) functional at the generalized gradient approximation

156

(GGA-PBE) was applied in this work.37-39 More detailed processes on the calculations

157

of the interactions between rGO and phenols were provided in SI.

158

RESULTS AND DISCUSSION

159

Characterization of rGO material. The TEM image of rGO (Figure 1A) exhibited a

160

crumpled and wrinkled flake-like structure. The ultrathin nature of graphene

161

nanosheets made them nearly invisible unless the relative clear multilayered stacks.10

162

The surface functional groups of rGO were determined by FTIR spectroscopy. As

163

illustrated in Figure 1B, the bands at ~ 3435 and 1400 cm-1 were ascribed to the -OH

164

stretching and bending vibration. The strong band at 1589 cm-1 was attributed to the

165

aromatic C=C stretching vibration, and another strong band at 1104 cm-1 was ascribed

166

to C-O stretching vibration.9,40 These functional groups were further evidenced from

167

the high deconvolution of C 1S XPS spectrum. As shown in Figure 1C, the carbon

168

existed mainly in three forms, i.e., nonoxygenated carbon (C=C, 284.8 eV), the

169

carbon in C-O group (286.4 eV), and the carbonyl carbon (C=O, 289.5 eV). However,

170

the carboxylate carbon (O=C-O) was not determined due to its low content.41 In

171

addition, the proportion of C=C:C-O:C=O obtained from the proportion of

172

C=C:C-O:C=O XPS peak acreage was 4.6:1.5:1 (Table S1). These functional groups

173

provided abundant reactive sites for the sorption of phenols. The pH value at the zero 8


Page 8 of 32

Page 9 of 32


174

point charge (pHZPC) of rGO was calculated to be 5.6 from the potentiometric

175

acid-base titration curve (Figure 1D), which indicated that the rGO was highly

176

positively charged at pH < 5.6. Conversely, the surface charge of rGO was negative at

177

pH > 5.6.

178

Removal of phenol and naphthol. A series of systematic experiments were

179

performed to evaluate the removal capacities of phenol and naphthol by the prepared

180

rGO. Sorption kinetic tests were first carried out to determine the contact time needed

181

for sorption equilibrium. As can be seen from Figure 2A-B, the phenol and naphthol

182

were adsorbed rapidly at the first 4 h, and thereafter it proceeded at a slow rate and

183

finally attained saturation after 6 h of contact time. At the initial state, the phenols

184

were adsorbed onto the rGO surface easily, and the accumulation of molecules on the

185

surface finally resulted in a low sorption rate in the later stage with contact time

186

increased.42 The relative parameters of pseudo-first-order and pseudo-second-order

187

models (Table S2) clearly confirmed that the sorption of phenol and naphthol on rGO

188

was dominated by the pseudo-first-order model.

189

The neutral or anion form of phenols was determined by their pKa versus the solution

190

pH values (Table S3). At pH < pKa, the nondissociated neutral species were

191

dominated for phenols while the anion forms were dominant at pH > pKa. Figure

192

2C-D showed the effect of pH on the sorption of phenol and naphthol. The removal

193

efficiency of phenol and naphthol increased with solution pH increasing until it

194

reached its pKa. The pHPZC of rGO (5.6) indicated that the surface of rGO was mainly

195

negatively charged at pH > 5.6. Therefore, the reduced sorption of phenol and 9



196

naphthol at pH > pKa was mainly owing to the increased electrostatic repulsion

197

between the negatively charged rGO and the dissociated phenols.43 The dissociation

198

of phenols increased their hydrophilicity, so the decreased sorption at pH > pKa was

199

also due to the reduced hydrophobic interactions.44 Furthermore, the dissociation of

200

the -OH group of the phenols was disadvantageous to form the hydrogen bonds

201

between the surfaces of rGO and phenolic molecules, and thereby reduced the

202

removal as well.7,44 Increased sorption of phenol and naphthol to rGO with increasing

203

pH before their pKa may be due to the enhanced π-π interactions. Other

204

investigators44,45 documented that the increased sorption of phenol, naphthol,

205

1,2,4-trichlorobenzene and 2,4-dinitrotoluene to carbon nanotubes (CNTs) with the

206

increase of pH at pH < pKa. They demonstrated that the increasing pH could change

207

the properties of polar aromatics, such as the π-donating strength, and therefore

208

improved the sorption to CNTs, but the interaction mechanism was still unclear.

209

Figure 2E-F showed the sorption isotherms of phenol and naphthol on rGO at the

210

temperatures of 298, 313 and 328 K, respectively. The removal of phenols on rGO

211

increased with increasing temperature, demonstrating that high temperature was

212

beneficial for phenols' sorption on rGO. The relative parameters calculated from the

213

Freundlich and Langmuir models (Table S4) showed that the Langmuir model fitted

214

the sorption isotherms better than the Freundlich model, revealing that the sorption of

215

phenols on rGO was monolayer coverage. The qmax value of phenol sorption on rGO

216

(2.7 mmol/g at 298 K) was slightly higher than that of naphthol (2.3 mmol/g), which

217

was negatively related to molecular size: 22.6 Å2 for phenol and 35.6 Å2 for naphthol 10


Page 10 of 32

Page 11 of 32


218

(Figure S2). Such a phenomenon was also reported by other investigators46,47, where

219

the authors concluded that the pore-filling mechanism dominated the sorption of

220

polycyclic aromatic hydrocarbons on carbon-based materials.

221

To understand the competitive sorption behavior of two different compounds on the

222

surface of rGO, the competitive removal of phenol and naphthol was investigated

223

under different pH and contact time (Figure 2A-D). Clearly, the sorption of phenol

224

and naphthol on rGO were decreased in binary system over the wide pH range, which

225

was consistent with the removal of aromatic organic pollutants onto MWCNTs.27,47

226

The rGO has a limited number of sorption sites for both phenol and naphthol

227

molecules to occupy competitively, thereby resulted in the decreased sorption in the

228

binary systems. The competitive sorption isotherms of phenol and naphthol on rGO at

229

298 K were shown in Figure 2E-F. The competitive Langmuir model was used to fit

230

the experimental isotherm data (Figure S3). For the competitive sorption, the qmax

231

values decreased from 2.7 to 1.5 mmol/g for phenol and from 2.3 to 1.6 mmol/g for

232

naphthol, revealing a higher sorption configurations of rGO for naphthol than phenol.

233

Furthermore, it was well known that sorption of phenols was controlled by a

234

combination of hydrophobic interactions, π-π interactions and hydrogen-bonding

235

interactions.7,43,44 The strength of π-π interactions, hydrophobic interactions and

236

hydrogen-bonding interactions relied on the solute π-polarity ability (π*),

237

octane-water distribution coefficient (Kow) and hydrogen-bonding acceptor ability

238

(βm), respectively, which were closely link with the aromatic ring number. According

239

to logKow, π* and βm values of phenol (logKow = 1.46, π* = 0.37 and βm = 0.33) and 11



240

naphthol (logKow = 2.84, π* = 0.47 and βm = 0.33), it was reasonable that naphthol

241

had very strong competitive sorption effect to phenol owing to its extra

242

benzene-rings.44,48 However, the qmax values of phenol and naphthol (i.e., 1.5 mmol/g

243

for phenol and 1.6 mmol/g for naphthol) were higher than that of phenol single

244

system (2.7 mmol/g) and that of naphthol single system (2.3 mmol/g), suggesting that

245

the sorption capacities of rGO were increased for the coexisting of multi-components.

246

The increased amounts of phenol and naphthol on rGO at binary system could be

247

attributed to the intra-molecular interactions between the phenols themselves. Due to

248

the hydrogen bond interactions between hydroxyl groups in naphthol and

249

oxygen-containing functional groups in rGO, the hydroxyl groups of naphthol were

250

preferentially attracted to rGO surfaces and left the hydrophobic benzene rings to face

251

the water molecular in solution. The unoccupied benzene ring of naphthol could

252

supply new sorption active sites, thus a second layer of phenol would be adsorbed to

253

the initially adsorbed naphthol molecules by hydrophobic as well as π-π interactions

254

between benzene rings. As shown in Figure S4, significant sorption of phenol by

255

naphthol confirmed the molecule-molecule attractions between different solutes. The

256

same reaction mechanism was applied to explain the competitive sorption of aromatic

257

organic compounds on MWCNTs and rGO.10,47,49 These findings indicated that the

258

rGO was very suitable materials for the simultaneous elimination of organic

259

pollutants from aqueous solutions.

260

Discussion on removal mechanism

261

Spectroscopic techniques. To understand the interaction mechanism of rGO with 12


Page 12 of 32

Page 13 of 32


262

phenol and naphthol, the rGO samples after pollutant sorption were characterized by

263

FTIR and Raman techniques. Figure 3A showed the FTIR spectra of rGO before and

264

after the sorption of phenol and naphthol. It was obvious that the stretching vibration

265

of C=C band was shifted from 1589 cm-1 to 1585 cm-1 after phenol sorption and to

266

1576 cm-1 after naphthol sorption. It was in line with the previous observations that

267

π-π conjugative effect and hydrophobic interactions occurred between rGO and

268

phenols.10,26 McDermott and McCreery50 pointed out that the graphite basal plane in

269

the vicinity of the edges was usually electron-rich, whereas the regions in the

270

graphene surface center were typically electron-depleted. Therefore, π-π electron

271

donor-acceptor interaction was occurred between the π-electron-rich phenyls of

272

phenols and the π-electron-deficient matrix of graphene nanosheets. In addition, the

273

hydroxyl groups were electron-donating functional groups, which could enhance the

274

π-donating strength of host aromatic ring.44 Thereby, the -OH could improve the

275

sorption ability of phenols to the surfaces of rGO via π-π interaction. Similarly, Chen

276

et al.51 documented that π-π interaction lead to stronger removal of the amino- and

277

hydroxyl-replaced aromatic compounds than the nonpolar aromatic compounds to

278

CNTs. In addition, small shifts in the -OH bond were observed after sorption, from

279

3435 to 3428 cm-1 after phenol sorption and from 3435 to 3430 cm-1 after naphthol

280

sorption. Jin et al.9 also reported that -OH bond of rGO changed after the sorption, i.e.,

281

from 3444 to 3415 cm-1 for 4-n-nonylphenol and from 3444 to 3428 cm-1 for

282

bisphenol A. The substituent hydroxyl group on phenol molecules may form hydrogen

283

bonds with the O-containing polar moieties on rGO. The proposed mechanism was 13



284

further supported by Raman spectroscopy analysis (Figure 3B), the G band (∼1580

285

cm-1) was related to the vibration of sp2 carbon atoms in the 2-dimensional hexagonal

286

lattice of graphite, and the D band (∼1350 cm-1) was assigned to the vibrations of the

287

defected and disordered sp3 carbon atoms.52 The weak and broad 2D peak at ∼2700

288

cm-1 was an out-of-plane vibration mode which was another indication of disorder

289

consquence.52 The ratio of D and G band intensities (ID/IG) was a common index

290

about the extent of defects on the surfaces of rGO. Noteworthy from Figure 3B, the

291

intensity ratios of ID/IG of rGO-phenol (0.93) and rGO-naphthol (0.95) were larger

292

than that of rGO (0.91). This implied that the size of the “graphene-like” domains was

293

smaller than those before sorption, however it was much more numerous in the

294

number.53

295

Theoretical calculations. The snapshots for the gradual sorption process of phenol

296

and naphthol were shown in Figures 4 and 5, respectively. The final closest interaction

297

distances of phenol and naphthol were 3.503 and 3.438 Å, respectively. Thus,

298

naphthol may have stronger π-π interaction with rGO plane than phenol. This

299

conclusion was further proved by the sorption energy (Es) calculations. The Es was

300

calculated by the formula: Es=E[A]+E[B]-E[total], where E[total] represented the total

301

energy of the target complex system, E[A] was the total energy of rGO, and E[B] was

302

the total energy of the isolated phenol or naphthol molecule. The calculated Es in

303

Table S5 showed that the rGO-phenols system was stable and rGO was effective

304

adsorbent for the removal of phenols pollutants from natural environment. The more

305

positive the Es is, the more stable the system is.54 The Es of naphthol-rGO was higher 14


Page 14 of 32

Page 15 of 32


306

than that of phenol-rGO indicated the naphthol-rGO system had stronger stability,

307

which agreed well with the competitive sorption experimental observations.

308

Interestingly, in aqueous solutions, except for the sorption between phenols and rGO,

309

there were also inter- or intra-molecular interactions between the phenols themselves.

310

The initial physical or chemical properties of the adsorbed molecules themselves may

311

play an important role during the sorption process. Thus, furthermore, the MD

312

simulations were performed in solution box to explore the initial interactions between

313

the adsorbed molecules. The MD simulation details were shown in SI. The total

314

hydrogen bond numbers, diffusion constant, solvent accessible surface area (SASA)

315

were computed using the g_hbond, g_msd and g_sas tool of the Gromacs Program

316

package, respectively.55 From the self-diffusion constants calculated from the theory

317

(Table S6), one may draw the conclusion that the self-diffusivity in naphthol packed

318

solution box (1.54 × 10-5 cm2s-1) was a little higher than that of phenol (1.53 × 10-5

319

cm2s-1), while their mixture showed much higher self-diffusivity of 2.73 × 10-5 cm2s-1.

320

Generally, the diffusion constant reflected the diffusivity and mobility of molecule to

321

a certain extent. The higher the diffusivity, the faster it diffuses and this will

322

eventually influence the sorption process. The hydrogen bond numbers of different

323

reactants were shown in Figure 6. The hydrogen bond number in individual phenol or

324

naphthol was quite same. When the phenol and naphthol molecules were mixed, they

325

were apt to form hydrogen bonds between phenol and naphthol other than phenol or

326

naphthol themselves individually, since the formation frequency of phenol-naphthol

327

was much dense than the ones in phenol or naphthol alone. Therefore, the different 15



328

formation pattern of hydrogen bond was probably another important factor in sorption.

329

The SASA reflected the surface area of a molecule that was accessible to solvent.

330

Figure 7 showed that the hydrophilic and hydrophobic SASAs of naphthol were larger

331

than that of phenol. Since the naphthol molecule possessed one more aromatic ring

332

than the phenol molecule, which was benefit for the formation of π-π and

333

hydrophobic interactions. In addition, from the calculated curves, the naphthol system

334

was much more fluctuant than the smooth ones in the phenol system, which showed

335

the instability of the naphthol clusters. Based on the above analysis, one can conclude

336

that the interaction of phenols with rGO was mainly dominated by hydrophobic

337

interactions, π-π interactions and hydrogen bonds.

338

Environmental implications. Phenols were regarded as priority contaminants

339

because they are harmful to organisms at low levels and can be toxic when present

340

elevated concentrations and are suspected to be carcinogens.7 Hence, it was regarded

341

particularly important and urgent to eliminate the phenols from industrial effluents

342

before discharging into the aqueous solution. Graphene is expected to have excellent

343

sorption capacity toward phenols organic compounds, and has the potential to be

344

applied as a superior adsorbent in wastewater and drinking water treatments.19 For the

345

first time, we systematic studied the sorption of phenol and naphthol on rGO and

346

demonstrated their interaction process by MD simulation and DFT calculations. The

347

batch experimental results proved that the sorption of phenols on rGO was highly

348

dependent on solution chemistry. When compared with phenol, naphthol exhibited a

349

higher sorption energy with rGO. In binary phenol-naphthol system, naphthol 16


Page 16 of 32

Page 17 of 32


350

presented a greater inhibition of the removal of phenol. The competitive sorption of

351

phenols on rGO in multiple organic contaminants systems was mainly dependent on

352

their chemical properties and the experimental conditions. The findings were crucial

353

to assess the removal of coexisting aromatic organic pollutants on rGO and offered an

354

indication of future directions to synthesize new kinds of nanomaterials for the

355

simultaneous elimination of organic pollutants from wastewater.

356

ASSOCIATED CONTENT

357

Supporting Information. Additional preparation of GO and rGO. More detailed

358

processes and information of MD simulation and DFT calculation. The relative

359

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

360

Internet at http://pubs.acs.org.

361

AUTHOR INFORMATION

362

Corresponding Authors. Tel(Fax):86-10-61772890; e-mail: [email protected]

363

(X.K. Wang); [email protected] (Y.J. Ai).

364

Notes

365

The authors declare no competing financial interest.

366

ACKNOWLEDGMENTS

367

The authors acknowledged the National Natural Science Foundation of China

368

(91326202, 21225730, 21577032 and 21403064), the Science Challenge Project

369

(JCKY2016212A04), the Fundamental Research Funds for Central Universities

370

(JB2015001). X. Wang acknowledged the CAS Interdisciplinary Innovation Team of

371

Chinese Academy of Sciences. 17



372

REFERENCES

373

(1) Ali, I. New generation adsorbents for water treatment. Chem. Rev. 2012, 112,

374

5073-5091.

375

(2) Khajeh, M.; Laurent, S.; Dastafkan, K. Nanoadsorbents: classification, preparation,

376

and applications (with emphasis on aqueous media). Chem. Rev. 2013, 113,

377

7728-7768.

378

(3) Thomas, A. G.; Syres, K. L. Adsorption of organic molecules on rutile TiO2 and

379

anatase TiO2 single crystal surfaces. Chem. Soc. Rev. 2012, 41, 4207-4217.

380

(4) Canivet, J.; Fateeva, A.; Guo, Y.; Coasne, B. Water adsorption in MOFs:

381

fundamentals and applications. Chem. Soc. Rev. 2014, 43, 5594-5617.

382

(5) Ribeiro, R. S.; Silva, A. M. T.; Figueiredo, J. L.; Faria, J. L.; Gomes, H. T.

383

Catalytic wet peroxide oxidation: a route towards the application of hybrid magnetic

384

carbon nanocomposites for the degradation of organic pollutants. A review. Appl.

385

Catal. B: Environ. 2016, 187, 428-460.

386

(6) Dias, E. M.; Petit, C. Towards the use of metal-organic frameworks for water

387

reuse: a review of the recent advances in the field of organic pollutants removal and

388

degradation and the next steps in the field. J. Mater. Chem. A 2015, 3, 22484-22506.

389

(7) Yang, K.; Wu, W.; Jing, Q.; Zhu, L. Aqueous adsorption of aniline, phenol, and

390

their substitutes by multi-walled carbon nanotubes. Environ. Sci. Technol. 2008, 42,

391

7931-7936.

392

(8) Zou, Y.; Wang, X.; Khan, A.; Wang, P.; Liu, Y.; Alsaedi, A.; Hayat, T.; Wang, X.

393

Environmental remediation and application of nanoscale zero-valent iron and its 18


Page 18 of 32

Page 19 of 32


394

composites for the removal of heavy metal ions: a review. Environ. Sci. Technol. 2016,

395

50, 7290-7304.

396

(9) Jin, Z.; Wang, X.; Sun, Y.; Ai, Y.; Wang, X. Adsorption of 4-n-nonylphenol and

397

bisphenol-A on magnetic reduced graphene oxides: a combined experimental and

398

theoretical studies. Environ. Sci. Technol. 2015, 49, 9168-9175.

399

(10) Yu, S.; Wang, X.; Ai, Y.; Tan, X.; Hayat, T.; Hu, W.; Wang, X. Experimental and

400

theoretical studies on competitive adsorption of aromatic compounds on reduced

401

graphene oxides. J. Mater. Chem. A 2016, 4, 5654-5662.

402

(11) Li, J.; Fan, Q.; Wu, Y.; Wang, X.; Chen, C.; Tang, Z.; Wang, X. Magnetic

403

polydopamine decorated with Mg-Al LDH nanoflakes as a novel bio-based adsorbent

404

for simultaneous removal of potentially toxic metals and anionic dyes. J. Mater. Chem.

405

A 2016, 4, 1737-1746.

406

(12) Altenor, S.; Carene, B.; Emmanuel, E.; Lambert, J.; Ehrhardt, J. J.; Gaspard, S.

407

Adsorption studies of methylene blue and phenol onto vetiver roots activated carbon

408

prepared by chemical activation. J. Hazard. Mater. 2009, 165, 1029-1039.

409

(13) Özkaya, B. Adsorption and desorption of phenol on activated carbon and a

410

comparison of isotherm models. J. Hazard. Mater. 2006, 129, 158-163.

411

(14) Przepiórski, J. Enhanced adsorption of phenol from water by ammonia-treated

412

activated carbon. J. Hazard. Mater. 2006, 135, 453-456.

413

(15) Alkaram, U. F.; Mukhlis, A. A.; Al-Dujaili, A. H. The removal of phenol from

414

aqueous solutions by adsorption using surfactant-modified bentonite and kaolinite. J.

415

Hazard. Mater. 2009, 169, 324-332. 19



416

(16) Radian, A.; Mishael, Y. Effect of humic acid on pyrene removal from water by

417

polycation-clay mineral composites and activated carbon. Environ. Sci. Technol. 2012,

418

46, 6228-6235.

419

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

420

adsorption of nitroaromatic compounds on graphene oxide, reduced graphene oxide,

421

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

422

(18) Kian, P. L.; Bao, Q.; Priscilla, K.; Yang, J. The chemistry of graphene. J. Mater.

423

Chem. 2010, 20, 2277-2289.

424

(19) Zhao, J.; Wang, Z.; White, J. C.; Xing, B. Graphene in the aquatic environment:

425

adsorption, dispersion, toxicity and transformation. Environ. Sci. Technol. 2014, 48,

426

9995-10009.

427

(20) Pei, Z.; Li, L.; Sun, L.; Zhang, S.; Shan, X.; Yang, S.; Wen, B. Adsorption

428

characteristics of 1,2,4-trichlorobenzene, 2,4,6-trichlorophenol, 2-naphthol and

429

naphthalene on graphene and graphene oxide. Carbon 2013, 51, 156-163.

430

(21) Zhao, J.; Wang, Z.; Zhao, Q.; Xing, B. Adsorption of phenanthrene on multilayer

431

graphene as affected by surfactant and exfoliation. Environ. Sci. Technol. 2014, 48,

432

331-319.

433

(22) Shen, Y.; Chen, B. Sulfonated graphene nanosheets as a superb adsorbent for

434

various environmental pollutants in water. Environ. Sci. Technol. 2015, 49,

435

7364-7372.

436

(23) Wang, X.; Qin, Y.; Zhu, L.; Tang, H. Nitrogen-doped reduced graphene oxide as

437

a bifunctional material for removing bisphenols: synergistic effect between adsorption 20


Page 20 of 32

Page 21 of 32


438

and catalysis. Environ. Sci. Technol. 2015, 49, 6855-6864.

439

(24) Wang, J.; Chen, B.; Xing, B. Wrinkles and folds of activated graphene

440

nanosheets as fast and efficient adsorptive sites for hydrophobic organic contaminants.

441

Environ. Sci. Technol. 2016, 50, 3798-3808.

442

(25) Song, W.; Yang, T.; Wang, X.; Sun, Y.; Ai, Y.; Sheng, G.; Hayat, T.; Wang, X.

443

Experimental and theoretical evidence for competitive interactions of tetracycline and

444

sulfamethazine with reduced graphene oxides. Environ. Sci: Nano 2016, 3,

445

1318-1326.

446

(26) Ren, H.; Kulkarni, D. D.; Kodiyath, R.; Xu, W.; Choi, I.; Tsukruk, V. V.

447

Competitive adsorption of dopamine and rhodamine 6G on the surface of graphene

448

oxide. ACS Appl. Mater. Interfaces 2014, 6, 2459-2470.

449

(27) Yang, K.; Wu, W.; Jing, Q.; Jiang, W.; Xing, B. Competitive adsorption of

450

naphthalene with 2,4-dichlorophenol and 4-chloroaniline on multiwalled carbon

451

nanotubes. Environ. Sci. Technol. 2010, 44, 3021-3027.

452

(28) Matsui, Y.; Yoshida, T.; Nakao, S.; Knappe, D. R. U.; Matsushita, T.

453

Characteristics of competitive adsorption between 2-methylisoborneol and natural

454

organic matter on superfine and conventionally sized powdered activated carbons.

455

Water Res. 2012, 46, 4741-4749.

456

(29) Yang, L.; Zhang, Y.; Liu, X.; Jiang, X.; Zhang, Z.; Zhang, T.; Zhang, L. The

457

investigation of synergistic and competitive interaction between dye Congo red and

458

methyl blue on magnetic MnFe2O4. Chem. Eng. J. 2014, 246, 88-96.

459

(30) Zhang, F.; Song, Y.; Song, S.; Zhang, R.; Hou, W. Synthesis of 21



460

magnetite-graphene oxide-layered double hydroxide composites and applications for

461

the removal of Pb(II) and 2,4-dichlorophenoxyacetic acid from aqueous solutions.

462

ACS Appl. Mater. Interfaces 2015, 7, 7251-7263.

463

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

464

Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via

465

chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558-1565.

466

(32) Ho, Y. S.; McKay, G. Sorption of dye from aqueous solution by peat. Chem. Eng.

467

J. 1998, 70, 115-124.

468

(33) Ho, Y. S. Review of second-order models for adsorption systems. J. Hazard.

469

Mater. 2006, 136, 681-689.

470

(34) Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and

471

platinum. J. Am. Chem. Soc. 1918, 40, 1361-1403.

472

(35) Freundlich, H. M. F. Uber die adsorption in lusungen. J. Phys. Chem. 1906, 57,

473

385-470.

474

(36) Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy

475

calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169-11186.

476

(37) Methfessel, M.; Paxton, A. T. High-precision sampling for Brillouin-zone

477

integration in metals. Phys. Rev. B 1989, 40, 3616-3621.

478

(38) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation

479

made simple. Phys. Rev. Lett. 1996, 77, 3865-3868.

480

(39) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation

481

made simple. Phys. Rev. Lett. 1997, 78, 1396-1396. 22


Page 22 of 32

Page 23 of 32


482

(40) Sun, Y.; Yang, S.; Chen, Y.; Ding, C.; Cheng, W.; Wang, X. Adsorption and

483

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

484

theoretical study. Environ. Sci. Technol. 2015, 49, 4255-4262.

485

(41) Yu, S.; Wang, X.; Tan, X.; Wang, X. Sorption of radionuclides from aqueous

486

systems onto graphene oxide-based materials: a review. Inorg. Chem. Front. 2015, 2,

487

593-612.

488

(42) Hu, J.; Shao, D.; Chen, C.; Sheng, G.; Ren, X.; Wang, X. Removal of

489

1-naphthylamine from aqueous solution by multiwall carbon nanotubes/iron

490

oxides/cyclodextrin composite. J. Hazard. Mater. 2011, 185, 463-471.

491

(43) Pan, B.; Xing, B. Adsorption mechanisms of organic chemicals on carbon

492

nanotubes. Environ. Sci. Technol. 2008, 42, 9005-9013.

493

(44) Dao, L.; Xing, B. Adsorption of phenolic compounds by carbon nanotubes: role

494

of aromaticity and substitution of hydroxyl groups. Environ. Sci. Technol. 2008, 42,

495

7254-7259.

496

(45) Chen, W.; Duan, L.; Zhu, D. Adsorption of polar and nonpolar organic chemicals

497

to carbon nanotubes. Environ. Sci. Technol. 2007, 41, 8295-8300.

498

(46) Sun, Y.; Yang, S.; Zhao, G.; Wang, Q.; Wang, X. Adsorption of polycyclic

499

aromatic hydrocarbons on graphene oxides and reduced graphene oxides. Chem.

500

Asian J. 2013, 8, 2755-2761.

501

(47) Yang, K.; Wu, X.; Zhu, L.; Xing, B. Competitive sorption of pyrene,

502

phenanthrene, and naphthalene on multiwalled carbon nanotubes. Environ. Sci.

503

Technol. 2006, 40, 5804-5810. 23



504

(48) Kaibara, A.; Hirose, M.; Nakagawa, T. Effect of the polar functional group of the

505

solute on hydrophobic interaction with the stationary ligand in reversed-phase

506

high-performance liquid chromatography. Chromatographia 1990, 29, 551-556.

507

(49) Wang, X.; Tao, S.; Xing, B. Sorption and competition of aromatic compounds

508

and humic acid on multiwalled carbon nanotubes. Environ. Sci. Technol. 2009, 43,

509

6214-6219.

510

(50) McDermott, M. T.; McCreery, R. L. Scanning tunneling microscopy of ordered

511

graphite and glassy carbon surfaces: electronic control of quinone adsorption.

512

Langmuir 1994, 10, 4307-4314.

513

(51) Chen, W.; Duan, L.; Wang, L.; Zhu, D. Adsorption of hydroxyl- and

514

amino-substituted aromatics to carbon nanotubes. Environ. Sci. Technol. 2008, 42,

515

6862-6868.

516

(52) Zhao, G.; Li, J.; Ren, X.; Chen, C.; Wang, X. Few-layered graphene oxide

517

nanosheets as superior sorbents for heavy metal ion pollution management. Environ.

518

Sci. Technol. 2011, 45, 10454-10462.

519

(53) Yin, F.; Wu, S.; Wang, Y.; Wu, L.; Yuan, P.; Wang, X. Self-assembly of mildly

520

reduced graphene oxide monolayer for enhanced Raman scattering. J. Solid State

521

Chem. 2016, 237, 57-63.

522

(54) Yu, S.; Wang, X.; Ai, Y.; Liang, Y.; Ji, Y.; Li, J.; Hayat, T.; Alsaedi, A.; Wang, X.

523

Spectroscopic and theoretical study on the counterion effect of Cu(II) ions and

524

graphene oxide interaction with titanium dioxide. Environ. Sci: Nano 2016, 3,

525

1361-1368. 24


Page 24 of 32

Page 25 of 32


526

(55) Hess, B.; Kutzner, C.; van der Spoel, D.; Lindahl, E. Gromacs 4: algorithms for

527

highly efficient, load-balanced, and scalable molecular simulation. J. Chem. Theory

528

Comput. 2008, 4, 435-447.

529

25



530 531

Figure 1. The characterization of rGO: (A) TEM image; (B) FTIR spectrum; (C) C 1s

532

XPS spectrum; (D) potentiometric acid-base titrations.

26


Page 26 of 32

Page 27 of 32


533 534

Figure 2. Effect of time (A and B), pH (C and D) and temperature (E and F) on phenol

535

and naphthol sorption onto rGO. C0 = 25 mg/L, I = 0.01 mol/L NaClO4, m/V = 0.1 g/L.

536

Sorption isotherms of phenol (E) and naphthol (F) in a single system at different

537

temperature and in binary system at T = 298 K on rGO at pH = 6.5 ± 0.1. The solid

538

lines represent the Langmuir model. The dashed lines represent the Freundlich

539

model. 27



540 541

Figure 3. The characterization of rGO before and after the sorption of phenol and

542

naphthol: (A) FTIR spectra; (B) Raman spectra.

543 544

Figure 4. The snapshots of the MD trajectory for the sorption process of phenol (a)

545

and the optimized static structure for the phenol-rGO system from the side view (b)

546

and the top view (c).

28


Page 28 of 32

Page 29 of 32


547 548

Figure 5. The snapshots of the MD trajectory for the sorption process of naphthol (a)

549

and the optimized static structure for the naphthol-rGO system from the side view (b)

550

and the top view (c).

29



551 552

Figure 6. (A) Dynamical properties analyses of hydrogen bonds for the phenol (a) and

553

naphthol (b) in the individual solution boxes. (B) Dynamical properties analyses of

554

hydrogen bonds for the phenol (a), naphthol (b) and phenol-naphthol (c) in the mixed

555

solution boxes.

30


Page 30 of 32

Page 31 of 32


556 557

Figure 7. Dynamical properties analyses of solvent accessible surface area (SASA,

558

nm2) for the phenol (A) and naphthol (B) in solution boxes.

559

31



560

TOC

561

Competitive sorption of phenol and naphthol on reduced graphene oxide (rGO).

562

32


Page 32 of 32

Macroscopic, Spectroscopic, and Theoretical Investigation for the

Recommend Documents