Thermal modification of molybdenum disulfide surface for tremendous

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Article

Thermal modification of molybdenum disulfide surface for tremendous improvement of Hg2+ adsorption from aqueous solution Feifei Jia, Chang Liu, Bingqiao Yang, Xian Zhang, Hao Yi, Jiaming Ni, and Shaoxian Song ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01412 • Publication Date (Web): 21 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

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 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 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.

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 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

1

Thermal modification of molybdenum disulfide

2

surface for tremendous improvement of Hg2+

3

adsorption from aqueous solution

4 5

Feifei Jia1, Chang Liu1, Bingqiao Yang2, Xian Zhang1, Hao Yi1, Jiaming Ni1,

6

Shaoxian Song1,3,4 ∗

7 8

1

9

Technology, Luoshi Road 122, Wuhan, Hubei, 430070, China

School of Resources and Environmental Engineering, Wuhan University of

10

2

11

Wuhan, Hubei, 430073, China

12

3

13

University of Technology, Luoshi Road 122, Wuhan, Hubei, 430070, China

14

4

15

Vanadium Resources, Wuhan University of Technology, Luoshi Road 122, Wuhan,

16

Hubei, 430070, China

Xingfa Mining School, Wuhan Institute of Technology, Xiongchu Avenue 693,

Hubei Key Laboratory of Mineral Resources Processing and Environment, Wuhan

Hubei Provincial Collaborative Innovation Center for High Efficient Utilization of

17

∗

Corresponding author. Tel: +862787212127. E-mail: [email protected]

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

18

Abstract

19

The adsorption of Hg2+ on thermally modified molybdenum disulfide was

20

explored in this work. The XPS and HRTEM results revealed that thermal treatment

21

led to partial oxidation of MoS2 to MoO3 and a creation of edge defects on the surface

22

of molybdenum disulfide. The DFT calculation indicated that the oxidative etchings

23

were terminated with oxygen atoms, and both the vacancy and perfect surface could

24

be oxidized during thermal treatment. The batch tests indicated that thermal treatment

25

enabled the surface of molybdenum disulfide highly reactive as Hg2+ adsorbent. The

26

adsorption rate and capacity on 500oC heated molybdenum disulfide was 17.6 times

27

faster and 11 folds higher compared to that of molybdenum disulfide without thermal

28

modification. The tremendous enhancement on Hg2+ adsorption was significantly

29

related to the oxidation of molybdenum disulfide and the increase of atom activity on

30

the surface. The oxidation could provide O active sites to strongly adsorb Hg through

31

the formation of Hg-O complex, while the increased activity greatly improved the

32

affinity of Hg to molybdenum disulfide. This work suggests that thermal modification

33

is an efficient method to increase the removal capacity of heavy metals on

34

molybdenum disulfide.

35

Keywords: molybdenum disulfide; Hg2+ adsorption; thermal modification; oxidation

36 37

Introduction

38

Molybdenum disulfide (MoS2), a typical layered transition metal dichalcogenite,

39

has attracted tremendous research interest in the past few years due to its prominent


Page 2 of 31

Page 3 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40

mechanical and optoelectronic properties that completely different from its bulk

41

molybdenite phase.1 By virtue of the direct band gap and high mobility value,

42

molybdenum disulfide possesses enormous potentials in electronics, chemical sensors,

43

biomedical, catalysis, and energy-related fields.2–5 Furthermore, the latest researches

44

show that molybdenum disulfide has substantial potentials in environmental

45

applications because of its huge surface-to-volume ratio and strong adsorption

46

capacity.6–8

47

Among the advances of molybdenum disulfide in environmental fields, the

48

application in contaminant adsorption, especially the removal of heavy metals from

49

water, is critically discussed.9 It was reported that the Hg2+ adsorption capacity of

50

molybdenum disulfide resulted from a natural molybdenite was 305 mg/g.10 The

51

porous MoS2 aerogel exhibited a 1527 mg/g Hg2+ uptake capacity and decreased the

52

Hg2+ level in contaminated water from 10 mg/L to 0.11 µg/L within a few minutes.11

53

Molybdenum disulfide nanosheets with widened interlayer spacing reached an

54

extremely high Hg2+ adsorption capacity (2587 mg/g), which was even higher than the

55

theoretically predicted value (2506 mg/g) on the assumption of a 1:1 stoichiometric

56

S/Hg ratio, as well as fast adsorption kinetics and excellent Hg2+ selectivity.12 In

57

addition, molybdenum disulfide also presents enormous advantages as adsorbent for

58

the removal of other heavy metal ions such as Pb2+, Co2+, Cd2+.8,13,14 The superb

59

uptake capacity of molybdenum disulfide to heavy metals was mainly attributed to the

60

strong complexation between the exposed (001) planes of molybdenum disulfide and

61

the heavy metal ions.



62

Our previous work demonstrated that the (001) basal surface of natural

63

molybdenum disulfide were chemically reactive for the heavy metals, nonetheless it

64

exhibited far lower Hg2+ uptake capacity than the synthesized molybdenum

65

disulfide.15 In my view, the surface property of molybdenum disulfide might be of

66

significant importance in the adsorption of Hg2+, however, no profound investigation

67

has concerned on this topic.

68

In this work, an attempt was made to study the role of surface property of

69

molybdenum disulfide in its Hg2+ adsorption. The surface of molybdenum disulfide

70

was modified through a simple thermal treatment. The surface property after thermal

71

treatment was studied by transmission electron microscopy (TEM), X-ray

72

photoelectron spectroscopy (XPS), Raman spectroscopy, as well as a theoretical

73

density functional theory (DFT) calculation. The Hg2+ adsorption performance was

74

investigated through AFM observation, adsorption thermodynamics and kinetics

75

experiments. The mechanism of the enhanced Hg2+ adsorption on molybdenum

76

disulfide was interpreted through XPS determination. The object was to obtain a clear

77

understanding in the effect, as well as the influence mechanism, of surface property of

78

molybdenum disulfide on its adsorption to heavy metals, furthermore to give a precise

79

guidance for the preparation of molybdenum disulfide as superb adsorbent.

80 81

Experimental section

82

Materials

83

Natural molybdenite collected from the Wuzhou mine, Guangxi province, China,


Page 4 of 31

Page 5 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


84

was used in this work for the preparation of molybdenum disulfide. X-ray diffraction

85

pattern (XRD) indicated the high purity of the sample (shown in Fig. S1). The

86

thermogravimetry analysis (TGA) and differential thermal analysis (DTA) of

87

molybdenite were given in Fig. S2. At temperature below 460oC, no obvious weight

88

loss was observed, indicating no obvious change of composition. After that, the

89

weight decreased with the increase of temperature and reached a plateau at around

90

680oC, during which the sharp decrease occurred at 550oC. The approximate 10% of

91

the weight loss in this range might be ascribed to the oxidation of MoS2. The dramatic

92

decrease of the weight loss at temperature higher than 750oC was probably resulted

93

from the composition of sample.

94

Mercuric nitrate (Hg(NO3)2·H2O) purchased from Shanghai Zhanyun Chemical

95

Co., Ltd (China), nitric acid and sodium hydroxide purchased from Sinopharm

96

Chemical Reagent Co., Ltd (China) were of analytical grade. Milli-Q water with a

97

resistivity of 18.2 MΩ·cm was used in all the experiments.

98 99 100

Methods Preparation of molybdenum disulfide nanosheets

101

Molybdenum disulfide nanosheets were prepared with an ultrasound assisted

102

electrochemical exfoliation method, during which bulk molybdenite was positioned as

103

a cathode electrode. The details of the preparation procedure were given in our

104

previous work.8 The obtained molybdenum disulfide nanosheet was named as M in

105

this study.



106

Page 6 of 31

Thermal modification of molybdenum disulfide

107

The surface property of molybdenum disulfide was modified through a simple

108

thermal treatment. 10 grams of molybdenum disulfide nanosheets were first placed in

109

an agate crucible, followed by putting the crucible in a muffle furnace (Vulcan 3-550).

110

The samples were thermally treated from room temperature to a given value (400oC

111

and 500oC) with a heating rate of 10oC/min and the set temperature was kept constant

112

for 2 h. After cooling down, the samples were washed with deionized water and

113

filtrated

114

(4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt). Molybdenum disulfide

115

nanosheets subsequent to 400oC and 500oC thermal treatment were named as M-400

116

and M-500, respectively.

until

no

MoO42-

was

detected

in

the

filtrate

with

tiron

117 118

AFM study on Hg2+ adsorption on bulk molybdenum disulfide

119

One drop of 100 µg/L Hg2+ solution prepared with Hg(NO3)2·H2O and deionized

120

water was firstly placed on the surface of bulk molybdenum disulfide with and

121

without thermal treatment for a desired time. After that the surface was washed with

122

deionized water for several times to remove the un-adsorbed Hg2+ and dried in air.

123

The surface morphology was then observed using AFM. Subsequently, the sample

124

was further adsorbed with Hg2+ and the surface morphology of the sample was

125

recorded with AFM.

126 127

Routine experimental of Hg2+ adsorption on molybdenum disulfide nanosheets


Page 7 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


128

Batch experiments were conducted to study the adsorption of Hg2+ on

129

molybdenum disulfide before and after thermal treatment. Firstly, a given amount of

130

adsorbent was added into Hg(NO3)2·H2O solution with desired Hg2+ concentration

131

and pH. The suspension was then shaken in a water bath shaker for predetermined

132

time intervals at room temperature and shaking rate of 150 rpm. After that, 5 ml

133

suspension was filtered with 0.22 µm filter membrane, during which the first 2 ml

134

filtrate was discarded and another 3 ml was collected for the chemical analysis of

135

Hg2+. For the adsorption kinetic experiment, 50 mg molybdenum disulfide nanosheets

136

were added into 1 L 50 mg/L Hg2+ solution and adsorbed for different time intervals

137

(0-400 min). For the adsorption isotherm experiments, 10 mg of the adsorbent was

138

added into 150 ml Hg2+ solution with concentration of 25-200 mg/L. The pH of

139

solutions were maintained at 6.0±0.1 in the adsorption kinetics and isotherm

140

experiments. While, 10 mg of the adsorbent was added into 160 ml 50 mg/L Hg2+

141

solution with pH ranging from 1 to 6 when studying the pH effect on the adsorption.

142

Mercury adsorption capacity is estimated by the following expression:

143

q = V0 (C0 - C) / m

(1)

144

where q is the adsorption capacity of the adsorbent, mg/g; C0 and C represent the Hg2+

145

concentration before and after adsorption, respectively, mg/L; V0 is the solution

146

volume, L; m is the mass of the adsorbent, g.

147 148 149

Computational methods The DFT calculations were used to interpret the defect formation on MoS2, as



Page 8 of 31

150

well as the stable structure of defective MoS2. The MoS2 structures were subjected to

151

periodic boundary condition with a supercell geometry. 2.0 nm vacuum space was

152

constructed to eliminate the interaction between the adjacent MoS2 layers. All the

153

computations were performed using all-electron DFT with a double numerical basis

154

set plus dynamic polarization function (DNP), as implemented in the Dmol3 module.

155

The Perdew-Burke-Ernzerhof (PBE) of Generalized Gradient Approximation (GGA)

156

was applied as exchange correlation function. In relaxation, a Monkhorst-Pack k-point

157

mesh of 2×1×1 was chosen for the structure optimization. The adsorption energy,

158

Ead, of O2 adsorbed on molybdenum disulfide, is defined as

Ead = EM +O2 − EM − EO2

159

(2)

160

where EM+O is the total energy of molybdenum disulfide with adsorbed O2, EM and

161

EO correspond to the energy of molybdenum disulfide and of the isolated O2 molecule,

162

respectively. The oxidation energy is described by the equation as follows:16,17

2

2

∆E = Eoxidized − E pristine − xµo + yµs

163

(3)

164

where Eoxidized and Epristine are the energies of the oxidized and pristine MoS2; µo and µs

165

are the reference chemical potentials of O and S atoms, x and y are the numbers of

166

added O and removed S atoms, respectively. For the experimental condition

167

performed at 500oC and one bar, the value of µo and µs are -0.75 and -2.64 eV,

168

respectively, calculated from the gas-phase O2 molecule and α-phase of solid sulfur

169

(S8).

170 171

Measurements


Page 9 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


172

Bruker MultiMode 8 AFM was used for the observation of surface morphology

173

and thickness of molybdenum disulfide, as well as Hg2+ adsorption on bulk

174

molybdenite. The measurement was performed in PeakForce mode with

175

ScanAsyst-Air silicon nitride probe (nominal tip radius of 2 nm) on V-shaped

176

cantilever (resonance frequency fo=70 kHz, spring constant k=0.4 N/m, dimensions of

177

115 µm×25 µm×650 nm), during which the images were captured with 512 pixels and

178

automatically optimized scan parameters (setpoint, feedback response, and scan rate).

179

The obtained images were analyzed with NanoScope Analysis 1.5 software, in which

180

the images were flattened in second order without further process.

181

Raman spectra were obtained from INVIA Raman microscope with a 514 nm Ar

182

laser (Renishaw, UK). The concentration of Hg2+ was detected using a contrAA700

183

continuum source atomic absorption spectrometer (Jena, Germany). The HRTEM

184

images were observed by using a Tecnai G2 F30 S-TWIN transmission electron

185

microscope (FEI, United States). XPS analysis was performed with an ESCALB

186

250Xi photoelectron spectrometer using Al Kα radiation (Thermo-Fisher Scientific,

187

US).

188 189

Results and discussion

190

Characterization of molybdenum disulfide before thermal modification

191

A representative AFM image of mica surface with deposition of molybdenum

192

disulfide nanosheets was shown in Fig. 1a. The lateral size of these nanosheets ranged

193

from dozens of nanometers to hundreds of nanometers. The similar height color



194

indicated the uniform thickness of these nanosheets. The inset figure displayed the

195

height of the corresponding cross-section profile of the molybdenum disulfide

196

nanosheet marked with the line. The step height from the substrate to the nanosheet

197

was around 1.3 nm, which was almost double of the step height measured from AFM

198

for a monolayer S–Mo–S structure (0.7 nm),18 therefore the marked nanosheet might

199

be bilayer molybdenum disulfide. To make further efforts on the presentation of

200

thickness distribution, 200 nanosheets were randomly selected and the result was

201

given in Fig. 1b. It showed that no nanosheets with step height less than 0.8 nm were

202

detected, suggesting that few molybdenum disulfide nanosheets presented as a single

203

layer. It could be observed that most of the nanosheets had thickness ranging from 0.9

204

nm to 1.6 nm, demonstrating that the majority of the sheets belonged to bilayer

205

molybdenum disulfide.

206 207

Fig. 1. AFM characterization of molybdenum disulfide, (a) representative AFM image, the inset

208

figure is the corresponding height cross-section profile of the nanosheet marked with a line, (b)

209

histogram of the thickness distribution of molybdenum disulfide nanosheets.

210 211

A representative TEM image of molybdenum disulfide before thermal treatment

212

was shown in Fig. 4a. The good transparency to visible light indicated the thin


Page 10 of 31

Page 11 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


213

thickness of molybdenum disulfide. However, no individual thin nanosheets were

214

observed and most of the sheets existed in the form of stacking, which was probably

215

because that the individual sheets were not stopped by the copper grid during the

216

preparation of TEM sample due to their small lateral size.

217 218

Characterization of molybdenum disulfide after thermal modification

219

XPS was performed to determine the chemical composition on the surface of

220

molybdenum disulfide. The wide-scan XPS spectra of molybdenum disulfide before

221

and after thermal treatment were presented in Fig. 2a. The O peaks at around 531 eV

222

and 975 eV became clear on the thermally treated molybdenum disulfide and their

223

intensity increased with the increase of treating temperature, suggesting that oxidation

224

occurred on molybdenum disulfide during thermal treatment. Fig. 2b displayed the

225

Mo3d spectra of molybdenum disulfide before and after being thermally treated. There

226

were two characteristic peaks of MoS2 at 229 eV [Mo3d5/2], 232 eV [Mo3d3/2] and a S2s

227

peak at 226 eV on M. After being thermally treated at 400oC, the intensity of MoS2

228

[Mo3d5/2] and S2s peaks reduced and a new peak at 235 eV corresponded to MoO3

229

clearly appeared, indicating the partial transformation of MoS2 to MoO3. The decrease

230

in MoS2 [Mo3d5/2], S2s peaks and the increase in MoO3 peak became more remarkable

231

on M-500, demonstrating a further oxidation of MoS2 to MoO3 when increasing the

232

thermal treating temperature to 500oC.



233 234 235

Fig. 2. XPS spectra of molybdenum disulfide nanosheets before and after thermal modification (a) wide-scan XPS spectra, (b) high-resolution Mo3d spectra.

236

237 238 239

Fig. 3. Raman spectra of molybdenum disulfide nanosheets before and after thermal treatment.

240

Fig. 3 showed the Raman spectra of molybdenum disulfide nanosheets before

241

and after thermal treatment, where the characteristic in-plane E12g mode and

242

out-of-plane A1g mode of molybdenum disulfide were observed. No obvious Raman

243

shift occurred on the peaks of M-400, indicating that the thickness of molybdenum

244

disulfide nanosheets did not change after 400oC thermal treatment. While, a slight

245

reduction of the frequency differences between the E12g and A1g modes was observed


Page 12 of 31

Page 13 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


246

on M-500, suggesting the tiny thinning of molybdenum disulfide layers.19 In addition,

247

a minor decreasing in the intensity of A1g mode occurred on M-500, which might be

248

caused by a slight oxidation of molybdenum disulfide during the 500oC

249

modification.20

250 251

Fig. 4. HRTEM images of molybdenum disulfide (a) without thermal treatment, (b) thermally

252

treated at 400oC, (c) thermally treated at 500oC.

253 254

Fig. 4 showed the HRTEM images of molybdenum disulfide before and after



255

thermal treatment. Although small sheets stacking on big sheets were observed,

256

individual sheet had homogeneous transparency, indicating that molybdenum

257

disulfide without thermal treatment was of high crystallinity (Fig. 4a). While after

258

being thermally treated at 400oC, the transparency differed in different regions on the

259

sheet, suggesting that the crystallinity might be reduced in the thermal treatment (Fig.

260

4b). Small defects with dimension of several nanometers were observed on M-400 as

261

pointed out by the arrows in Fig. 4b. As a comparison, lots of etching with dozens of

262

or even hundreds of nanometers in size appeared on molybdenum disulfide sheets

263

after 500oC thermal treatment (Fig. 4c), being clear evident for the presence of defects

264

on M-500. In addition, more defects were observed on M-500 than that on M-400.

265

The results indicated that both the size and the density of defects would increase if

266

molybdenum disulfide was thermally treated at higher temperature, which was highly

267

consistent with the previous work.21,22

268 269

Formation of defects and oxidation of MoS2

270

Partial oxidation and defects were observed on molybdenum disulfide during

271

thermal treatment based on the results of XPS, Raman spectra, and HRTEM. Here

272

DFT calculation was performed to interpret the formation of defects and occurance of

273

oxidation during thermal treatment. The configuration before the O2 adsorption on

274

defective molybdenum disulfide was presented in Fig. 5a and 5b. The O2 was placed

275

above the S vacancy with the O-O bond being vertical to the (001) basal plane of

276

MoS2. It should be mentioned that MoS2 structure with one single S missing was built


Page 14 of 31

Page 15 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


277

because one S vacancy was the predominate defect existed on MoS2 due to the lowest

278

defect formation energy.23,24 After the geometric structure optimization and transition

279

state search, one oxygen atom located in the S vacancy site and was bound with three

280

Mo atoms, and another oxygen atom was bound with one S atom near the S vacancy

281

(Fig. 5d and 5e). The optimized structure was in good agreement with other

282

research.23 The calculated adsorption energy of O2 on defective MoS2 was -3.07 eV,

283

indicating that the oxidation of MoS2 was thermodynamically favorable. In addition,

284

the low adsorption energy, which was in the range of typical covalent bond energy,

285

demonstrated a chemisorption for O2 on the surface of defective MoS2. Fig. 5d and 5e

286

also showed that the bond length between O(1) and adjacent Mo was even shorter than

287

that between S and adjacent Mo, which gave another strong evidence for the chemical

288

reaction of O(1) and Mo. The electron density map shown in Fig. 5c displayed that no

289

overlap of electron cloud was being observed between O and Mo or S before the

290

adsorption of O2, while obvious overlaps between O(1) and Mo atoms, O(2) and S atom

291

were observed after the adsorption (Fig. 5f), strongly proving the formation of

292

molybdenum oxide and sulfur oxide. While these formed oxides would evaporate

293

when the surrounding temperature was high, leaving bigger vacancy.21,25,26 If more O2

294

were incorporated into the system, more molybdenum oxide and sulfur oxide would

295

emerge on the structure of MoS2, and those oxides would disappear as well under

296

thermal treatment. In this way, the etching pits enlarged and large defects formed.



297 298

Fig. 5. Configurations and electron density maps of MoS2 before and after the reaction with O2.

299

Fig. 5a, 5b and 5c are the top, side view of configuration and electron density map before O2

300

adsorption, respectively, while Fig. 5d, 5e and 5f are the corresponding results after O2 adsorption.

301

The blue, yellow and red balls indicate Mo, S and O atoms, respectively.

302 303

In order to illustrate the terminals of the defects, the structure energy of 50% and

304

100% edge oxidized MoS2 (shown in Fig. 6b and 6c, respectively) was calculated in

305

comparison with the energy of pristine structure with fully S saturated edge (Fig. 6a).

306

The oxidation energy per unit length for 50% and 100% edge oxidized MoS2 were

307

-1.10 and -2.11 eV/Å, respectively, calculated from Eq. (3). The negative values

308

suggested that the oxidized structure of MoS2 were more thermodynamically stable

309

than the pristine structure. And MoS2 with fully oxidized edge was the most stable

310

structure compared to the other two structures because of the lowest energy. The

311

results demonstrated that most of defects might terminate with oxygen atoms when no

312

more thermal energy was input.


Page 16 of 31

Page 17 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


313 314

Fig. 6. MoS2 configurations with different oxygen contents on the edge, 100% S (a), 50% O (b),

315

100% O (c). The blue, yellow and red balls indicate Mo, S and O atoms, respectively.

316 317

The oxidation of MoS2 on the basal plane was investigated through calculating

318

the energy of MoS2 structure with two S atoms on the basal plane substituted by two

319

O atoms. The oxygen substitution energy was calculated according to Eq. (3), where

320

the Eoxidized and Epristine were energies of MoS2 after geometric structure optimization

321

as shown in Fig. 7b and 100% O edge oxidized MoS2 as shown in Fig. 6c,

322

respectively. The calculated oxygen substitution energy was -0.36 eV/Å,

323

demonstrating that oxidation could also proceed on the basal plane of MoS2 at high

324

temperature and air atmosphere. In addition, the distance between O and Mo was

325

shorter than that between S and Mo, and the structure of MoS2 had slight modification

326

after optimization, further proving that Mo on the basal plane preferred to bind with O

327

other than S. However, due to the low activity of the basal atoms, oxidation of perfect

328

surface might lag behind that of the edge and vacancy sites.



329 330

Fig. 7. MoS2 configurations with two S atoms on the basal plane substituted by two O atoms

331

before (a) and after (b) geometric structure optimization. The blue, yellow and red balls indicate

332

Mo, S and O atoms, respectively.

333 334

Adsorption of Hg2+on molybdenum disulfide nanosheets before and after thermal

335

modification

336

The batch experimental results of Hg2+ adsorption kinetics on molybdenum

337

disulfide nanosheets before and after thermal modification were shown in Fig. 8a. The

338

adsorption increased fastly at initial times until it reached a plateau for the three

339

molybdenum disulfide nanosheets adsorbents. It can been seen that M exhibited the

340

lowest adsorption capacity at 50 mg/L initial Hg2+ concentration. After being treated

341

at 400oC, molybdenum disulfide nanosheets showed an enhanced Hg2+ adsorption

342

capacity, which was almost twice than that of M. While, the Hg2+ adsorption of

343

M-500 dramatically increased to 630 mg/g. These results indicated that thermal

344

treatment of molybdenum disulfide nanosheets significantly improved its Hg2+

345

adsorption capacity. A pseudo-first-order kinetic

346

pseudo-second-order kinetic model (Eq. S2) were used to fit the experimental data for


model (Eq. S1) and a

Page 18 of 31

Page 19 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


347

a further investigation of the adsorption mechanism. The fitting results are presented

348

in Fig. 8a and Table S1. The higher correlation coefficient of R22 indicated that the

349

Hg2+ adsorption on all the three molybdenum disulfide adsorbents was well-described

350

by the pseudo-second-order kinetic model, which was based on the assumption that

351

the rate-limiting step might be chemical sorption or chemisorption involving valence

352

forces through sharing or exchange of electrons between adsorbent and adsorbate.27

353

The fitting results demonstrated that chemical interaction might exist between Hg2+

354

and all the molybdenum disulfide adsorbents.

355

The initial adsorption rate, which was defined as the adsorbed Hg2+ per gram of

356

the adsorbent per unit time on the adsorbent in the first 5 min, was used to evaluate

357

the effect of thermal modification on the adsorption kinetics of Hg2+ on molybdenum

358

disulfide nanosheets (Fig. 8b). The adsorption rate of M-500 was 11.27 mg·g-1·min-1,

359

which was 17.6 and 5.3 times faster than that of M and M-400, respectively, further

360

proving the dramatical effect of thermal modification on the Hg2+ removal with

361

molybdenum disulfide nanosheets as adsorbent.

362 363

Fig. 8. Adsorption kinetics of Hg2+ on molybdenum disulfide nanosheets before and after thermal

364

treatment, (a) adsorption capacity as a function of time, (b) adsorption rate in the first 5 min. The



365

initial Hg2+ concentration and pH of the solution was 50 mg/L and 6, respectively.

366 367

The adsorption isotherms of Hg2+ on molybdenum disulfide nanosheets before

368

and after thermal modification at temperature of 30oC and pH of 6 were illustrated in

369

Fig. 9. The adsorption capacity increased with the increase of Hg2+ concentration until

370

it reached an equilibrium. The adsorption isotherm indicated an enormous adsorption

371

capacity of molybdenum disulfide nanosheets subsequent to thermal treatment. A 750

372

mg/g Hg2+ uptake capacity was obtained on M-500 at a Hg2+ equilibrium

373

concentration of around 110 mg/L, which was approximately 11 and 2.5 times higher

374

than that of M and M-400. These results indicated a better Hg2+ affinity on M-500

375

than on the other two adsorbents, which might be highly related to the modified

376

surface property of molybdenum disulfide during thermal treatment. It should be

377

mentioned that although a lower Hg2+ adsorption capacity was obtained on M, it was

378

still much higher than the traditional adsorbents (activated carbon, modified clay, etc.)

379

reported in other literatures.28,29

380 381

Fig. 9. Adsorption isotherm of Hg2+ on molybdenum disulfide nanosheets before and after thermal

382

treatment.


Page 20 of 31

Page 21 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


383

The adsorptions of Hg2+ on molybdenum disulfide nanosheets with and without

384

thermal treatment at pH range of 1-6 were illustrated in Fig. 10. All the three

385

adsorbents had low Hg2+ adsorption capacity at pH of 1, which might be because that

386

the presence of excess H+ in the solution would compete with Hg2+ for the active sites,

387

resulting in a low adsorption capacity. The adsorption capacity increased slightly with

388

the increase of pH for both M and M-400. While, the Hg2+ uptake capacity had a

389

dramatic enhancement on M-500 when increasing the pH of the solution to 2 and then

390

kept an equilibrium at higher pH values. Fig. 10 clearly suggested that thermal

391

modification enabled molybdenum disulfide to achieve a high Hg2+ affinity in a wide

392

pH range.

393 394

Fig. 10. Hg2+ adsorption on molybdenum disulfide nanosheets before and after thermal treatment

395

as a function of pH.

396 397

AFM observation of Hg2+ adsorption on bulk molybdenite

398

Due to the small size of exfoliated molybdenum disulfide, it is difficult to

399

observe the Hg2+ adsorption on its surface visually. To resolve this problem, bulk

400

molybdenite with large surface was chosen in this work to perform the Hg2+



401

adsorption on it and observed with AFM in order to give a better understanding on the

402

Hg2+ adsorption on molybdenum disulfide nanosheets. Bulk molybdenite had an

403

atomic smooth surface before thermal modification (Fig. 11a). After being exposed to

404

100 µg/L Hg2+ solution for 1 min, slight substances, which were confirmed to be Hg2+

405

in our previous work,10,15 were captured on the surface. The above results

406

demonstrated that the surface of molybdenite had chemical reactivity for the

407

adsorption of Hg2+. However, the adsorption of Hg2+ on molybdenite increased slowly

408

with the increase of adsorption time and less than half of the surface was occupied by

409

Hg2+ after 5 min adsorption, which indicated that the activity of the surface for Hg2+

410

was not strong. Fig. 11b illustrated the images of 500oC thermally modified

411

molybdenite with Hg2+ adsorption at different times, respectively. Lots of edge defects

412

were clearly detected on the sample before adsorption, further confirming the

413

existence of defects after being thermally treated. It was noticed that plenty of large

414

defects existed on bulk molybdenite, while only few defects with dimension of dozens

415

of nanometers were observed on molybdenum disulfide nanosheets at the same

416

thermal treatment condition (Fig. 4c). It was because that the oxidative etching was

417

greatly affected by the number of MoS2 layers and the pit sizes increased with the

418

increase of MoS2 layers.21 Plenty of Hg2+ distributed on the surface of thermally

419

treated molybdenite after 1 min adsorption, the density of which was similar with that

420

on 5 min Hg2+ adsorbed molybdenite. This indicated that thermal modification

421

accelerated the adsorption of Hg2+ on molybdenite. As the time increased, the Hg2+

422

adsorption on thermally treated molybdenite increased dramatically. The surface was


Page 22 of 31

Page 23 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


423

almost fully occupied by abundant Hg2+ within only 5 min. The defects on the surface

424

of molybdenite became obscure subsequent to 5 min Hg2+ adsorption, further

425

indicating the great Hg2+ adsorption capacity on thermally modified molybdenite.

426

These phenomena revealed that molybdenite was much more capable of capturing

427

Hg2+ after thermal modification. Due to the similar surface property of molybdenum

428

disulfide nanosheets and bulk molybdenite, it might be inferred that the surface of

429

molybdenum disulfide nanosheet was greatly activated during thermal treatment,

430

which was therefore bringing a significant enhancement on the Hg2+ adsorption.

431 432

Fig. 11. AFM images of Hg2+ adsorption on bulk molybdenite without (a) and (b) with thermal

433

modification at different times.

434 435

Origin of the enhanced Hg2+ adsorption on molybdenum disulfide after thermal

436

modification

437

XPS was performed to investigate the mechanism of Hg2+ adsorption on

438

molybdenum disulfide with and without thermal treatment. Compared with the

439

wide-scan XPS spectra of molybdenum disulfide before adsorption, new Hg peaks



440

appeared at around 101 eV, 106 eV, 360 eV, 380 eV, and 578 eV (Fig. 12a), which

441

gave a clear evidence for the Hg adsorption on molybdenum disulfide. Fig. 12b

442

compared the Hg4f5/2 and Hg4f7/2 spectra on the three adsorbents. Both of Hg4f peaks

443

were deconvoluted into two peaks, among which the doublet at 100 eV and 104 eV

444

could be assigned to Hg-S, while the other doublet at 101 eV and 105 eV might be

445

Hg-O. This revealed that both the intrinsic S and oxidation-resulted O served as the

446

binding sites for the immobilization of Hg on molybdenum disulfide. By comparing

447

the area proportion of Hg-O and Hg-S peaks, it could be obtained that S sites made a

448

bigger contribution than O sites on M for the adsorption of Hg, while the contribution

449

of the two sites were comparable to each other on M-400, and O sites even became

450

more important in the Hg adsorption on M-500. This phenomenon suggested the

451

significant role of oxidation of molybdenum disulfide in its Hg adsorption. In addition,

452

it was interesting to find out that although the content of S (30.7%) was higher than

453

that of O (20.6%) in 500oC thermally treated molybdenum disulfide, the chemisorbed

454

Hg2+ mainly presented in the form of Hg-O instead of Hg-S, which meant that O had a

455

better affinity than S in the chemisorption of Hg2+. No characteristic peak of Hg0 was

456

found in the range from 99 eV to 100 eV, indicating that no oxidation-reduction

457

reaction occurred on Hg2+ during the adsorption on molybdenum disulfide.30

458


Page 24 of 31

Page 25 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


459 460 461

Fig. 12. XPS spectra of molybdenum disulfide nanosheets with and without thermal treatment after Hg2+ adsorption (a) wide-scan XPS spectra, (b) high-resolution Hg4f spectra.

462 463

Conclusions

464

(1) Thermal treatment resulted in a partial oxidation of MoS2 to MoO3 and an

465

emergence of edge defects on the surface of molybdenum disulfide. The oxidation

466

and defects increased with the increase of thermal treatment temperature. DFT

467

calculation indicated that the oxidative etchings were terminated with oxygen

468

atoms, and both the vacancy and basal plane could be oxidized during thermal

469

treatment.

470

(2) The removal capacity of Hg2+ on molybdenum disulfide was significantly

471

enhanced after thermal modification. Molybdenum disulfide subsequent to 500oC

472

thermal treatment reached 17.6 times faster on the adsorption rate and 11 times

473

higher on the adsorption capacity than molybdenum disulfide without

474

modification. The pH effect results revealed that thermally modified molybdenum

475

disulfide exhibited a higher Hg2+ adsorption than that without thermal treatment in

476

all the pH values.



477

(3) Thermal treatment enabled molybdenum disulfide achieve a tremendous

478

enhancement on the Hg2+ adsorption, which might be greatly related to the higher

479

activity of the adsorbent surface and the formation of molybdenum oxide in

480

thermal treatment. XPS revealed that molybdenum oxide could strongly bind Hg2+

481

through the formation of Hg-O complexation.

482

(4) The tremendous enhancement of Hg2+ adsorption on molybdenum disulfide after

483

thermal treatment suggests that thermal modification is an efficient method for

484

molybdenum disulfide to increase its removal capacity of heavy metals.

485 486 487 488

Supporting Information X-ray diffraction (XRD) pattern, thermogravimetry analysis (TGA) and differential thermal analysis (DTA) of natural molybdenite.

489 490

Acknowledgements

491

The financial supports for this work from the National Natural Science

492

Foundation of China (51704220, 51674183 and 51704212), Natural Science

493

Foundation of Hubei Province (2017CFB280), and China Postdoctoral Science

494

Foundation (2016M600621) were gratefully acknowledged.

495 496 497

Conflict of Interest The authors declare no competing financial interest.

498


Page 26 of 31

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


499

References

500

(1)

photoluminescence in monolayer MoS2. Nano Lett. 2010, 10, 1271–1275.

501 502

(2)

(3)

Sundaram, R.S.; Engel, M.; Lombardo, A.; Krupke, R.; Ferrari, A.C.; Steiner, M. Electroluminescence in single layer MoS2. Nano Lett. 2013, 13, 1416–1421.

505 506

Mak, K.F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T.F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 2010, 105, 2–5.

503 504

Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C.Y.; Galli, G.; Wang, F. Emerging

(4)

Kim, S.; Konar, A.; Hwang, W.; Lee, J.H.; Lee, J.; Yang, J.; Jung, C.; Kim, H.; Yoo, J.; Chio,

507

J.; Jin, Y. W.; Lee, S. Y; Jena, D.; Choi, W.; Kim, K. High-mobility and low-power thin-film

508

transistors based on multilayer MoS2 crystals. Nat. Commun. 2012, 3, 1011–1017.

509

(5)

Liu, C.; Wang, L.; Tang, Y.; Luo, S.; Liu, Y.; Zhang, S.; Zeng, Y.; Xu, Y. Vertical single or

510

few-layer MoS2 nanosheets rooting into TiO2 nanofibers for highly efficient photocatalytic

511

hydrogen evolution. Applied Catal. B, Environ. 2015, 164, 1–9.

512

(6)

Commun. 2013, 49, 10718–10720.

513 514

Sun, L.; Huang, H.; Peng, X. Laminar MoS2 membranes for molecule separation. Chem.

(7)

Zhao, H.; Yang, G.; Gao, X.; Pang, C. H.; Kingman, S. W.; Wu, T. Hg0 capture over

515

CoMoS/γ-Al2O3 with MoS2 nanosheets at low temperatures. Environ. Sci. Technol. 2015, 50,

516

1056–1064.

517

(8)

adsorbent for high-efficient Pb(II) removal from water. Appl. Mater. Today 2017, 9, 220–228.

518 519 520

Liu, C.; Jia, F.; Wang, Q.; Yang, B.; Song, S. Two-dimensional molybdenum disulfide as

(9)

Wang, Z.; Mi, B. Environmental applications of 2D molybdenum disulfide (MoS2) nanosheets. Environ. Sci. Technol. 2017, 51, 8229–8244.



521

(10)

adsorbent for removing Hg2+ from water. ACS Sustainable Chem. Eng. 2017, 5, 7410–7419.

522 523

Jia, F., Wang, Q., Wu, J., Li, Y., Song, S. Two-dimensional molybdenum disulfide as a superb

(11)

Zhi, L.; Zuo, W.; Chen, F.; Wang, B. 3D MoS2 composition aerogels as chemosensors and

524

adsorbents for colorimetric detection and high-capacity adsorption of Hg2+. ACS Sustainable

525

Chem. Eng. 2016, 4, 3398–3408.

526

(12)

Ai, K.; Ruan, C.; Shen, M.; Lu, L. MoS2 nanosheets with widened interlayer spacing for

527

high-efficiency removal of mercury in aquatic systems. Adv. Funct. Mater. 2016, 26, 5542–

528

5549.

529

(13)

Aghagoli, M. J.; Beyki, M. H.; Shemirani, F. Application of dahlia-like molybdenum disulfide

530

nanosheets for solid phase extraction of Co(II) in vegetable and water samples. Food Chem.

531

2017, 223, 8–15.

532

(14)

Wang, J.; Zhang, W.; Yue, X.; Yang, Q.; Liu, F.; Wang, Y.; Zhang, D.; Li, Z.; Wang, J.

533

One-pot synthesis of multifunctional magnetic ferrite-MoS2-carbon dots nanohybrid adsorbent

534

for efficient Pb(II) removal. J. Mater. Chem. A 2016, 4, 3893–3900.

535

(15)

disulfide in aqueous solutions. Phys. Chem. Chem. Phys. 2017, 19, 3837–3844.

536 537

(16)

Santosh, K. C.; Longo, R. C.; Wallace, R. M.; Cho, K. Surface oxidation energetics and kinetics on MoS2 monolayer. J. Appl. Phys. 2015, 117, 135301−135308.

538 539

Jia, F.; Zhang X.; Song, S. AFM study on the adsorption of Hg2+ on natural molybdenum

(17)

Santosh, K. C.; Longo, R. C.; Addou, R.; Wallace, R. M.; Cho, K. Impact of intrinsic

540

atomic defects on the electronic structure of MoS2 monolayers. Nanotechnology 2014, 25,

541

375703−375708.

542

(18)

Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C. Y.; Galli, G.; Wang, F. Emerging


Page 28 of 31

Page 29 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


photoluminescence in monolayer MoS2. Nano Lett. 2010, 10, 1271–1275.

543 544

(19)

single- and few-layer MoS2. ACS Nano 2010, 4 (5), 2695–2700.

545 546

Lee, C.; Yan, H.; Brus, L. E.; Heinz, T. F.; Hone, J.; Ryu, S. Anomalous lattice vibrations of

(20)

Balendhran, S.; Ou, J. Z.; Bhaskaran, M.; Sriram, S.; Ippolito, S.; Vasic, Z.; Kats, E.;

547

Bhargava, S.; Zhuiykov, S.; Kalantarzadeh, K. Atomically thin layers of MoS2 via a two

548

step thermal evaporation-exfoliation method, Nanoscale 2012, 4, 461–466.

549

(21)

Zhou, H.; Yu, F.; Liu, Y.; Zou, X.; Cong, C.; et al. Thickness-dependent patterning of MoS2

550

sheets with well-oriented triangular pits by heating in air. Nano Research 2013, 6,

551

703−711.

552

(22)

atomically thin MoS2. J. Phys. Chem. C 2013, 117, 25643−25649.

553 554

Yamamoto, M.; Einstein, T. L.; Fuhrer, M. S.; Cullen, W. G. Anisotropic etching of

(23)

Zhao, B.; Shang, C.; Qi, N.; Chen Z. Y.; Chen, Z. Q. Stability of defects in monolayer MoS2

555

and their interaction with O2 molecule: A first-principles study. Applied Surface Science

556

2017, 412, 385−393.

557

(24)

Paul, J. F.; Payen, E. Vacancy formation on MoS2 hydrodesulfurization catalyst: DFT study of the mechanism. J. Phys. Chem. B. 2003, 107, 4057−4064.

558 559

(25) Najmaei, S.; Yuan, J.; Zhang, J.; Ajayan, P.; Lou, J. Synthesis and defect investigation of

560

two-dimensional molybdenum disulfide atomic layers. Acc. Chem. Res. 2015, 48, 31−40.

561

(26) Hong, J.; Hu, Z.; Probert, M.; Li, K.; Lv, D.; et al. Exploring atomic defects in molybdenum disulphide monolayers. Nat. Commun. 2015, 6, 6293−6300.

562 563 564

(27)

Ho, Y. S.; McKay, G. The kinetics of sorption of divalent metal ions onto sphagnum moss peat. Water Res. 2000, 34 (3), 735−742.



565

(28)

Krishnan, K. A.; Anirudhan, T. S. Removal of mercury(II) from aqueous solutions and

566

chlor-alkali industry effluent by steam activated and sulphurised activated carbons prepared

567

from bagasse pith: kinetics and equilibrium studies. J. Hazard. Mater. 2002, 92, 161–183.

568

(29)

Manohar, D. M.; Krishnan, K. A.; Anirudhan, T. S. Removal of mercury(II) from aqueous

569

solutions and chlor-alkali industry wastewater using 2-mercaptobenzimidazole-clay. Water

570

Research 2002, 36, 1609–1619.

571 572

(30)

Behra, P.; Bonnissel-Gissinger, P.; Alnot, M.; Revel, R.; Ehrhardt, J. J. XPS and XAS study of the sorption of Hg(II) onto pyrite. Langmuir 2001, 17 (13), 3970−3979.

573


Page 30 of 31

Page 31 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


574

For Table of Contents Use Only

575

576 577 578

TOC/Abstract Graphic Synopsis

579

Molybdenum disulfide achieves a tremendous enhancement on Hg2+ adsorption after

580

thermal treatment, mading it an excellent adsorbent for the sustainable reuse of

581

mercury contaminated water.


Thermal modification of molybdenum disulfide surface for tremendous

Recommend Documents