Synergistic deep removal of As(III) and Cd(II) by a calcined multifunctional MgZnFe-CO3 layered double hydroxide: Photooxidation, precipitation and adsorption

Accepted Manuscript Synergistic deep removal of As(III) and Cd(II) by a calcined multifunctional MgZnFeCO3 layered double hydroxide: Photooxidation, precipitation and adsorption Junqin Liu, Pingxiao Wu, Shuaishuai Li, Meiqing Chen, Wentin Cai, Dinghui Zou, Nengwu Zhu, Zhi Dang PII:

S0045-6535(19)30441-2

DOI:

https://doi.org/10.1016/j.chemosphere.2019.03.009

Reference:

CHEM 23323

To appear in:

ECSN

Received Date: 14 January 2019 Revised Date:

1 March 2019

Accepted Date: 3 March 2019

Please cite this article as: Liu, J., Wu, P., Li, S., Chen, M., Cai, W., Zou, D., Zhu, N., Dang, Z., Synergistic deep removal of As(III) and Cd(II) by a calcined multifunctional MgZnFe-CO3 layered double hydroxide: Photooxidation, precipitation and adsorption, Chemosphere (2019), doi: https:// doi.org/10.1016/j.chemosphere.2019.03.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Synergistic deep removal of As(III) and Cd(II) by a calcined multifunctional

2

MgZnFe-CO3 layered double hydroxide: Photooxidation, precipitation and

3

adsorption

4

Junqin Liua,b, Pingxiao Wua,b,c,d,e*, Shuaishuai Lia,b, Meiqing Chena,b, Wentin Caia,

5

Dinghui Zoua, Nengwu Zhua,b,e, Zhi Danga,b,c

6

a school of Environment and Energy, South China University of Technology,

7

Guangzhou 510006, P.R. China

8

b The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters,

9

Ministry of Education, Guangzhou 510006, P.R. China

M AN U

SC

RI PT

1

c Guangdong Provincial Engineering and Technology Research Center for

11

Environmental Risk Prevention and Emergency Disposal, South China University of

12

Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, PR

13

China

14

d Guangdong Engineering and Technology Research Center for Environmental

15

Nanomaterials, Guangzhou 510006, China

16

e Guangdong Environmental Protection Key Laboratory of Solid Waste Treatment

17

and Recycling, Guangzhou 510006, PR China

18

*Corresponding author

19

Tel.: +86-20-39380538;

20

Fax: +86-20-39383725.

21

E-mail: [email protected] (P.X. Wu).

AC C

EP

TE D

10

1

ACCEPTED MANUSCRIPT 22

Abstract A high removal rate (>99.7%) of combined arsenite (As(III)) and Cd (Cd(II)) in

24

low concentration (1000µg/L) from contaminated water was achieved by a calcined

25

MgZnFe-CO3 layered double hydroxide (CMZF) adsorbent. Batch control studies and

26

a series of spectroscopy detection technologies were employed to investigate the

27

removal mechanism and interactions between As(III) and Cd(II) on the interface of

28

water/CMZF. Synergistic adsorption and photooxidation occurred based on the

29

systematical kinetic and isotherm studies. The enhanced removal of As(III) was

30

achieved by the photooxidation, formation of ternary As(III)-Cd(II) surface

31

complexes and enhanced hydrogen bond. Meanwhile, oxidative formed negative

32

charged As(V) could reduce the electrostatic repulsion force between Cd(II) cations

33

and play a role as anion bridging, consequently resulted in a stronger attraction

34

between CMZF and Cd(II). Combined with the verdicts of relevant characterizations

35

such as XRD, XPS and EPR, it was assumed that the deep co-removal mechanism

36

could be attributed to the coupling of various processes including intercalation,

37

complexation, photooxidation of As(III) and precipitation of CdCO3. Moreover, the

38

successful removal of As(III) and Cd(II) from real water matrix qualified the CMZF a

39

potentially attractive adsorbent for both As(III) and Cd(II) deep treatment in practical

40

engineering.

41

Keywords: MgZnFe-CO3 layered double hydroxide; simultaneous adsorption; deep

42

removal; As(III) molecule; As (V) anion; Cd(II) cation

AC C

EP

TE D

M AN U

SC

RI PT

23

2

ACCEPTED MANUSCRIPT 43

1. Introduction Arsenic (As) and cadmium (Cd) are both notorious in water resource which can

45

cause advese effects, even in a trace concentration (Esposito et al., 2018), to ecosphere

46

and human body (Lofrano et al., 2016; Yu et al., 2016). As is commonly exist as

47

inorganic species of nonionized arsenite (As(III)) and oxyanions arsenate (As(V))

48

based on the redox conditions (Vaiano et al., 2018; Zhang et al., 2018a), As(III) is

49

much more hazardous than As(V) due to its more toxic, more mobile and less

50

adsorptive characteristics (Kim and Kim, 2014). While Cd is mainly exist as

51

hyper-toxic metal cation (Cd(II)) in various aquatic systems (Yoon et al., 2017).

52

Elevated levels of As and Cd contaminated water derived from industrial activities

53

and natural water (Yan et al., 2015; Genc-Fuhrman et al., 2016; Wu et al., 2018) has

54

raised serious concerns as it posed threats to human health through the food chain

55

accumulation and provision of drinking water (Chen et al., 2018; Li et al., 2018). Thus,

56

China has set limit for farming irrigation water that the concentration of As and Cd

57

shall not exceed 0.05 and 0.01 mg/L. The World Health Organization (WHO) also has

58

set guidelines for drinking water that the maximum allowable concentration is 10µg/L

59

and 3µg/L for As and Cd, respectively. (Wasana et al., 2017; Sun et al., 2018).

SC

M AN U

TE D

EP

AC C

60

RI PT

44

Heavy metals concentration in natural aqueous environment substantially

61

governed by mineral-surface interactions owning to the high affinity of minerals to

62

heavy metals (Zhang et al., 2018a). Thus metal oxides and metal hydroxides minerals

63

have been widely applied as adsorbents to remove As and Cd from the aqueous phase 3

ACCEPTED MANUSCRIPT in practical water treatment. So far, numerous techniques have been developed for the

65

removal of either As(III) or Cd(II) from water (Xie et al., 2016; López-Muñoz et al.,

66

2017; Huang et al., 2018). However, due to the different physicochemical properties

67

such as surface charge, ion form and redox activity between As(III) and Cd(II), it is

68

more challenging to removal them simultaneously, especially in low concentration

69

level (Li et al., 2018; Pawar et al., 2018). Furthermore, the interaction mechanism

70

including the competition/synergy effect, complexation model as well as the affinity

71

of As(III) and Cd(II) on the mineral surface has been rarely investigated, which seems

72

the key for their synchronous removal when they coexist in the aqueous environment.

M AN U

SC

RI PT

64

Layered double hydroxides (LDHs) is a class of hydroxide minerals with the

74

brucite-like layer structure, which is also well-know as the anionic clay. The general

75

formula of LDHs can be presented as [M1-xIIMxIII(OH)2]x+[Ax/n]n- mH2O, where MII

76

and MIII denote mental ions located on the positively charged octahedral sheets, An- is

77

exchangeable interlayer anion to neutralize the positive charge, X is range frome 0.17

78

to 0.33 (Lu et al., 2016; Yan et al., 2018). Calcination treatment is commonly

79

performed as pre-treated method to enhance the adsorption performance of LDHs

80

before application due to the elimination of interlayer substances (Lee et al., 2018; Yan

81

et al., 2018). In recent years, LDHs or calcined LDHs have been widely used as a

82

multifunctional material for environmental applications owing to their tunable metal

83

ions on brucite-like sheets and intercalated anions in hydrated interlayer regions

84

(Wang and O Hare, 2012; Fan et al., 2014). Fe based LDHs were used as adsorbent for

AC C

EP

TE D

73

4

ACCEPTED MANUSCRIPT As treatment based on the high affinity of iron phase surface towards As (Türk et al.,

86

2009; Zhang et al., 2014). Zn based LDHs were performed as photocatalyst to degrade

87

pollutants based on its appropriate valance and conduction band location contributed

88

from the derived zinc oxide (Parida and Mohapatra, 2012; Bouaziz et al., 2018). In

89

addition, the abundant functional hydroxyl groups (-OH) on the surface or various

90

intercalated anions also qualified LDHs as a promising material for metal cations

91

removal (González et al., 2015; Rahman et al., 2018). Thus there are reasons to believe

92

that LDHs particle will be a superior material for the treatment of combined As(III),

93

Cd(II) wastewater as well as an ideal medium to help dig out the underlying

94

interaction mechanisms between As(III) and Cd(II). Unfortunately, to the best of our

95

knowledge, no research has been done in this aspect.

SC

M AN U

In this research

a novel calcined MgZnFe-CO3 LDH (CMZF) was synthesized

TE D

96

RI PT

85

by a facile coprecipitation and calcination method. The prepared material exhibited an

98

outstanding removal efficiency for both As(III) and Cd(II) in low concentration level.

99

A systematic study including kinetic studies, isotherm studies and relevant

100

characterizations, such as SEM, XRD, XPS and EPR techniques, were investigated.

101

The objectives of this study is (1) to develop a high-efficient and low-cost adsorbent

102

for simultaneous depth treatment of As(III) and Cd(II) in contaminated water, (2) to

103

explore the interaction mechanisms between As(III) and Cd(II) pollutants in aqueous

104

environment, and (3) to explain the possible synergistic removal mechanisms of

105

As(III) and Cd(II) by CMZF adsorbent.

AC C

EP

97

5

ACCEPTED MANUSCRIPT 106 107

2. Materials and methods

108

2.1 Materials and chemicals Chemical reagents including nitrate salts (Mg(NO3)2·6H2O, Zn(NO3)2·6H2O,

110

Fe(NO3)3·9H2O, Cd(NO3)2·4H2O), nitric acid (HNO3), sodium hydroxide (NaOH)

111

and Sodium carbonate (Na2CO3) were obtained from Guangzhou Chemical Reagent

112

Factory (Guangzhou, P.R.C.). Sodium arsenite (NaAsO2) and disodium hydrogen

113

arsenate (Na2HAsO4·7H2O) were purchased from Sigma-Aldrich Chemical Company.

114

5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidone

115

(TEMP) were purchased from Aladdin Chemistry. The chemicals above are all

116

analytical reagent (AR) purity. The As(III), As(V) and Cd(II) stock solution were

117

obtained by adding adequate NaAsO2, Na2HAsO4 · 7H2O and Cd(NO3)2·4H2O to

118

deionized water respectively.

121

SC

M AN U

TE D

EP

120

2.2 Preparation of MgZnFe layered double hydroxides particles

AC C

119

RI PT

109

The MgZnFe layered double hydroxide (MZF LDH) and its calcined sample

122

(CMZF) were obtained using co-precipitation and calcination method, the detail was

123

shown in Text S1. For comparison, MgFe layered double hydroxide (MF LDH) and

124

its calcined sample (CMF) were synthesized followed by similar methods except for

125

adding zinc nitrate. All of the materials were ground into powder for further use.

126 6

ACCEPTED MANUSCRIPT 127

2.3 Characterization The X-ray diffraction (XRD) patterns of the materials were recorded by a D8

129

Advance diffractometer with Cu Ka radiation (λ= 1.5406 Å) at 40 kV and 40 mA. The

130

morphology and distribution of major elements were detected on a field-emission

131

scanning electron microscopy (SEM, Carl Zeiss, Germany) combined with

132

energy-dispersive X-ray spectroscopy (EDS). High-resolution transmission electron

133

microscopy (TEM) images were obtained by JEM-2100F field emission transmission

134

electron microscope with an accelerating voltage of 200 kV. Solid state UV-vis diffuse

135

reflectance spectra (UV-vis DRS) was recorded on a UV-2550 (Shimadzu, Japan)

136

spectrometer equipped with an integrating sphere within 190-900 nm wavelength

137

range. The Brunauer-Emmett-Teller (BET) specific surface area were investigated

138

utilizing a Micrometric ASAP 2020 analyzer. Thermogravimetric analysis (TGA)

139

were carried out on a Netzsch STA 409 PC/PG instrument under air atmosphere.

140

X-ray photoelectron-spectra (XPS) analysis was carried out on the X-ray

141

photoelectron spectrometer (AES430S, ANELVA, Japan). The ROS were identified

142

on an Electron Paramagnetic Resonance (EPR) Spectrometer Bruker A300 seted up as

143

center magnetic field of 3509.44 G, sweep width of 100 G, microwave frequency of

144

9.87GHz and power of 20.00 mW.

AC C

EP

TE D

M AN U

SC

RI PT

128

145 146 147

2.4 Experiment for As and Cd adsorption The batch kinetic adsorption experiments were carried out to estimate the 7

ACCEPTED MANUSCRIPT adsorption characteristics of Cd and As on LDH adsorbent. In details, 0.01g

149

adsorbents were added into 20 ml single or mixed solution of Cd and As obtained by

150

diluting the stock solution to desired concentration, then shaken in a

151

temperature-controlled rotary at 30±1 ℃ and pH of 6 under dark or irradiation

152

conditions. The simulated visible light source was provided by a 300 W xenon lamp.

153

After reaction has reached desired time, the suspension was filtered through a 0.45µm

154

filter membrane and the residual solution was collected for analysis. For isotherm

155

studies, 20 mL solution contain As(III)/As(V) or Cd(II) with the concentration

156

varying from 1 to 100 and 1-260 mg/L, respectively, was adjusted on pH to 6.0 and

157

then added with 10 mg of materials for 12 h oscillation to fit the Langmuir or

158

Freundlich model (Rehman et al., 2018), the model equations can be found in

159

supplement materials. The effect of pH on removal of As(III) and Cd(II) was studied

160

in a pH range of 3-10.0 adjusted by 0.1M NaOH or HNO3. The real water adsorption

161

was carried out using the spiked river water (added concentration of 429 µg/L As(III)

162

and 363 µg/L Cd (II), Pearl River, Guangdong Province, China. Detailed

163

water-quality index can be found in supplement materials, Table S4). The

164

concentrations of Cd(II) and total As in the obtained solutions were analyzed by

165

ICP-MS (Agilent, 7700, USA). The concentration of As(V) was analyzed by

166

spectrophotometric method based on the molybdenum blue at λ= 880nm (Vaiano et

167

al., 2014). All the experiments were conducted in triplicate and the average data were

168

presented with their standard deviations.

AC C

EP

TE D

M AN U

SC

RI PT

148

8

ACCEPTED MANUSCRIPT 169 3.Results and discussion

171

3.1 Characterization of as-prepared samples

172

3.1.1 XRD analysis

RI PT

170

The XRD patterns of MZF LDH and its calcined sample CMZF were depicted in

174

Fig. S1a. All the characteristic peaks including (003), (006), (009), (015), (018), (110)

175

and (113) could be found clearly in MZF LDH, meaning the well crystallographic

176

LDHs were synthesized. After calcination, the wide and weak spinel characteristic

177

peaks of MgFe2O4 (JCPDS No. 88-1943) or ZnFe2O4 (JCPDS no. 82-1042) (Wang et

178

al., 2017) were observed. The d spaces decreased from 0.78 to 0.25 nm after

179

calcination, indicating a partial interlayer molecules and ions were removed during

180

thermal treatment, which could improve the adsorption capacity by ion intercalation

181

during the layer reconstruction process (Kang et al., 2013).

184

M AN U

TE D

EP

183

3.1.2 Optical adsorption properties

AC C

182

SC

173

UV-vis DRS spectra and calculated band gap were recorded in Fig. S1b and c.

185

From S1b, the light adsorption of samples within visible-light range has been

186

improved significantly after calcination. That is possibly due to the topotactic

187

transformation of LDH during thermal treatment leading to a surface defects, resulting

188

in a red-shift of optical absorption (Lin et al., 2017). As a result, the band gap (Fig.

189

S1c) of CMZF became narrower compared with LDH. Noticeably, the band gap 9

ACCEPTED MANUSCRIPT distance were only 2.05 and 2.1 eV for CMZF and MZF LDH, respectively, meaning

191

the efficient utilization of photons which could results in more electron-hole pairs on

192

LDHs under illumination therefore leading to high photocatalytic activities (Zhang et

193

al., 2018).

194 3.1.3 Surface morphological and pore structure analysis

SC

195

RI PT

190

Fig. 1 presented the SEM, TEM and corresponding mapping images of the MZF

197

LDH and CMZF. The thin plate-like structure of MZF LDH and CMZF can be

198

observed clearly with the diameter around 200 nm., which is the typical morphology

199

for the LDHs based materials. While the TEM image of CMZF exhibited obvious

200

pore structure compared with MZF LDH, indicating the emerging of abundant

201

meso-pore after thermal treatment (details see Fig. S2). It is therefore leading to the

202

total pore volume and BET surface area of CMZF increased significantly (Table S1),

203

which play important roles for increasing the adsorption capacity. The different

204

electron diffractions (embedded graph) further proved the topotactic transformation

205

during thermal treatment, which was in agreement with the XRD result. The EDS and

206

mapping imagines of CMZF were presented in Fig. 1f. Mg, Zn and Fe are

207

homodisperse throughout the entire material, indicating the regularly Structured

208

arrangement of Mg, Zn and Fe in the layer sheets with the ratio of around 3:1:2. The

209

molecular-scale structure could be found in Fig. S3.

AC C

EP

TE D

M AN U

196

210 10

ACCEPTED MANUSCRIPT 211

3.2 Batch adsorption experiments

212

3.2.1 Effect of metal composition. The removal efficiency of Cd(II) and As(III) by MZF LDH, MF LDH and their

214

calcined samples was given in Fig. S5. Compared with MF LDH, MZF LDH showed

215

a higher As(III) removal but a lower Cd(II) removal efficiency. However the

216

difference of surface area pore volume and average pore diameter (Table S1) between

217

MF and MZF LDH is negligible, thus it was deduced that the element composition

218

rather than the structure played a key role for As(III) or Cd(II) selective adsorption.

219

Zn and Fe mainly responsible for As(III) adsorption, while Mg mainly responsible for

220

Cd(II) adsorption, which agree with the later XPS and SEM mapping results.

M AN U

SC

RI PT

213

221 3.2.2 Effect of pH and irradiation

TE D

222

The effect of pH and irradiation have been researched as shown in Fig. 2. In the

224

dark condition, As(III) mainly present as neutral H3AsO3 in a wide pH range from 1 to

225

9 (Zhu et al., 2018), thus the changing of surface charge of CMZF showed little effect

226

to the As(III) removal. Cd(II) mainly present as cation ion, the lower zeta potential of

227

CMZF could enhance the attraction between the surface hydroxyl groups and Cd(II)

228

at a higher pH. While under illumination, As(III) removal efficiency was improved to

229

a great extent whatever the pH was, proving that the CMZF had a great photocatalysis

230

property for improving As(III) removal. In the binary system of As(III) and Cd(II), no

231

obvious decrease was found in both As(III) and Cd(II) removal within all the pH

AC C

EP

223

11

ACCEPTED MANUSCRIPT range, but a little improve was observed at basic condition. Both the As and Cd

233

residual concentration met the WHO drink water standard (10µg and 3µg/L

234

respectively) when the pH was above 6. Additionally, the dissolved Fe level were

235

depicted in Fig. S6. Negligible leached Fe ion was detected (<4µg/L) within all pH

236

range above 4. All of these results indicate the great potential and safety of CMZF in

237

the actual application.

SC

RI PT

232

Zeta potentials of CMZF before and after reaction with As(III) and Cd(II) were

239

exhibited in Fig. S7, the isoelectric points of CMZF decreased from 3.4 to 3.2 (in

240

dark)/2.9 (in light) after adsorption of As(III) and increased to 3.6 after Cd(II)

241

adsorption. The isoelectric points could been shifted by the formation of

242

inter-sphere complexes based on the covalent or ionic bond (Goldberg and Johnston,

243

2001). Thus both the As(III) and Cd(II) adsorption process on the interface of CMZF

244

adsorbent could be concluded as not only an electrostatic adsorption, but also

245

characteristic adsorption.

247 248

TE D

EP AC C

246

M AN U

238

3.2.3 Kinetic studies

The removal efficiency is crucial for practical application engineering, kinetic

249

studies in the single or binary As(III) and Cd(II) system were conducted and the

250

results were displayed in Fig. 3. As shown in Fig. 3a, the CMZF exhibited a higher

251

adsorption efficiency toward As(V) compared with As(III). It could be ascribed to the

252

bigger As(V) group possess a stronger steric effect which qualified it more easily be 12

ACCEPTED MANUSCRIPT caught by surface defects of CMZF to form complexes (Mueller et al., 2010; Liu et al.,

254

2018). Besides, the extra O atom in the As(V) groups might also contributed

255

additional site for hydrogen bond. Fig. 3b displayed the light adsorption experiment,

256

the total As concentration decreased much faster and lower in the presence of light,

257

meaning the photo-oxidation played a crucial role enhancing As(III) uptake. The

258

generated As(V) concentration (see embedded graph of Fig. 3b) could further prove

259

this conclusion for it raised a little at fist 20 min due to higher oxidation rate of As(III)

260

to As(V) than adsorption, then dropped to an extremely low level by the combined

261

process of photocatalysis and adsorption. Kinetic curves in the binary As(III) and

262

Cd(II) systems were also recorded in Fig. 3c and d. From Fig. 3c, though As(III)

263

removal was enhanced in the dark by Cd(II), it still remain 37.2µg/L after 180min

264

adsorption, much higher than the drink water standard (10 µg/L). While only 3.4 µg/L

265

As with a unconspicuous adsorption decrease was found under illumination in the

266

binary system. Considering As(III) were presented as As(V) under the irradiation

267

condition, thus we proposed that Cd(II) can improve As(III) adsorption but decrease

268

the adsorption of As(V), which displayed a accordance with the later studies in binary

269

Cd(II) system. As shown in Fig. 3d, the removal of Cd(II) by CMZF was a fast

270

process with establishing a balance within 10 min and fell into a ultra low

271

concentration of 2.4 µg/L Cd(II) after 180min, indicating a strong interaction between

272

Cd(II) and CMZF (Chen et al., 2017). The additional As(III) improved Cd(II)

273

adsorption in the light while depressed Cd(II) in darkness, further proved that Cd(II)

AC C

EP

TE D

M AN U

SC

RI PT

253

13

ACCEPTED MANUSCRIPT could compete the adsorption site on CMZF with As(V). In this study, the equilibrium

275

pH was 8.5, thus the surface charge of CMZF (pHphz=3.4) was more favorable for

276

Cd(II) adsorption in neutral condition. On the other hand, the photo-generated

277

negative charged As(V) could meanwhile provide shielding effect (Zhu et al., 2015) to

278

compensate the positive repulsion between different Cd(II) leading to more accessible

279

adsorption sites for Cd(II), Cd(II) adsorption was therefore improved with As(III) in

280

the light. While As(III) was mainly present as neutral H3AsO3 in a wide pH range

281

from 1-9 (pKa=9.2) without lighting. The competition of Cd(II) to As(III) was

282

negligible compared with that of As(V). In contrary, Cd(II) can enhance As(III)

283

uptake through the formation of ternary surface complexation or coordination

284

complexes (Ren et al., 2016). Noticeably, the residual concentration of As(III) and

285

Cd(II) was below 10µg/L and 3 µg/L respectively in their both single or mixed

286

systems, well met the drinking water provision.

TE D

M AN U

SC

RI PT

274

289

3.2.4 Isotherm studies

AC C

288

EP

287

As depicted in Fig. 4, isotherm studies in single or mixed systems have been

290

investigated to better understand the coordination between As(III) and Cd(II). The

291

mass ratio of As to Cd was selected as 2:1 and 1:10 for As and Cd isotherms in the

292

mixed system respectively. The single As(III) and As(V) isotherms fitted both

293

Langmuir and Freundlich model well. That means As(III) and As(V) could form

294

multilayers on the adsorbent (Fig. S8a), which might attribute to the hydrogen bond 14

ACCEPTED MANUSCRIPT between O atom and hydroxyl group from different As groups. While the isotherms of

296

single Cd(II) fitted Langmuir model well with an incredible high adsorption constant

297

(K=1.37L/mg), suggesting the strong interaction involved in Cd(II) and CMZF

298

adsorbent. After the appearance of Cd(II), As(III) turn into Freundlich model and

299

As(V) transferred to Langmuir model respectively. That indicating the ternary surface

300

complexation or coordination happened between neutral As(III) and Cd(II). Besides,

301

due to Cd possesses a lower absolute electronegativity (1.69) than H (2.2) and As

302

(2.18) dose, the electron cloud density of adjoining O will be raised after

303

complexation with Cd thus leading to an enhanced hydrogen bond effect. While

304

owing to As(V) group has a higher electronegativity and negative charge compared

305

with As(III) groups, it is more difficult to approach the negative charged surface of

306

CMZF when Cd(II) appeared (Fig. S8b). In contrast, the coordinated deprotonated

307

As(V) could play a role as anion bridging to attract positive charged Cd(II) (Zhu et al.,

308

2016). Moreover, the dissociative As(V) could provide shielding effect to Cd(II), thus

309

the Cd(II) isotherm was changed into Freundlich model illustrated in Fig. 4d. These

310

analyses agree with that proposed in kinetic studies, As(III) can occupy the adsorption

311

site for Cd(II). While As(V) was weaker at the sites competition, which prefer to build

312

hydrogen bound rather than a direct sites adsorption thus improved the removal of

313

Cd(II) and As(III). In short, the competitiveness ranking of these three pollutants was

314

As(III) > Cd(II) >As(V). All the parameters of isotherms were given in Table S2 and

315

the Schematic diagrams were proposed in Fig. S8. Additionally, the maximum As and

AC C

EP

TE D

M AN U

SC

RI PT

295

15

ACCEPTED MANUSCRIPT Cd adsorption capacities of CMZF and previously reported adsorbents were compared

317

in Table S3. CMZF outperformed most of other adsorbents, indicating the CMZF

318

particle is a rather competitive alternative for As and Cd removal in actual water

319

treatment.

RI PT

316

320 3.2.5 Effect of ionic strength

SC

321

The effect of ionic strength on the removal of As(III) and Cd(II) by the CMZF

323

was depicted in Fig. S9. No significant decrease even a slight enhancement of As(III)

324

and Cd(II) removal was observed as the ionic strength increased from 0.1 mM to

325

10mM, indicating the good selectivity adsorption for As(III) and Cd(II) of CMZF.

326

Particularly, adsorption of ions via outer-sphere complexation is strongly effected by

327

ionic strength based on electrostatic force, as their adsorption is inhibited by

328

competition of weakly adsorbing ions (such as Na+, NO3-). On the contrary,

329

adsorption by inner-sphere coordination (ligand exchange) shows little sensitivity to

330

ionic strength with a stronger chemical bond (McBride, 1997). It further suggested

331

that both As(III) and Cd(II) were coordinated by CMZF to form stubborn inner-sphere

332

complexes.

334

TE D

EP

AC C

333

M AN U

322

3.2.6 Real water adsorption test.

335

Water matrix in reality is far more complex than deionized water as various

336

types of inorganic and organic matters will be generally contained in it. Test of 16

ACCEPTED MANUSCRIPT application of CMZF for practical As(III) and Cd(II) contaminated water treatment

338

was implemented using the spiked river water (Pearl River, Guangdong Province,

339

China, spiked concentration of 429 µg/L As(III) and 363 µg/L Cd (II) with 0.25 g/L

340

CMZF) and the result was displaced in Fig. S10. Apparently, CMZF effectively

341

removed both As(III) and Cd(II) under natural light or simulated visible light. All the

342

residual concentration of As(III) and Cd(II) were reduced to value lower than 10µg/L

343

and 3µg/L, respectively, after 6 h adsorption. That indicating the great potential of the

344

CMZF adsorbent on practical application for As(III) and Cd(II) deep removal.

345

M AN U

SC

RI PT

337

346

3.3 Removal mechanism analysis

347

3.3.1 Surface characterization using XPS

X-ray photoelectron spectroscopy (XPS) is a powerful tool for identify the

349

chemical state changes of elements in the upper atomic layers of solid surfaces. The

350

surface state of compositions of the CMZF before and after As(III) and Cd(II)

351

adsorption were characterized by XPS and the high-resolution scan of As3d,, C1s,

352

Fe2p and O1s core-level photoelectron spectra were presented in Fig. 5.

EP

AC C

353

TE D

348

As depicted in Fig. 5a, the binding energy peaks of As 3d after treatment of

354

As(III) solution in the dark and light conditions located at 44.3 and 45.4 eV, which

355

can be assigned to As(III) and As(V) respectively (Sun et al., 2017). These results

356

indicate that As adsorbed on to the CMZF was mainly As(III) in the dark

357

in the light, proving that the As(III) existed on the surface of CMZF could be 17

and As(V)

ACCEPTED MANUSCRIPT 358

efficiently oxidized to less toxic As(V) during the photooxidation process. The high-resolution scan of C 1s were shown in Fig. 5b, the peaks located at

360

288.5eV were attribute to the C=O (Singh et al., 2014) in CO32- at the surface or

361

interlayer of CMZF. After adsorption of Cd(II), a new peak appeared at 291 eV which

362

was attributed to the n-π* transition of C=O bound (M. and T. C., 2017). suggesting

363

that Cd(II) bounded onto the interlayer CO32- group and thus the electron density

364

towards the C=O is decreased (Irani et al., 2015). While after simultaneous treatment

365

of Cd(II) and As(III), an obviously decrease of the n-π* transition C=O bound was

366

observed, implying As(III) was more competitive to be exchanged into the CMZF

367

interlayer.

M AN U

SC

RI PT

359

Fig. 5c illustrated The high-resolution scan of Fe 2p, the binding energy value of

369

Fe2p 3/2 (711.4 eV) and Fe2p 1/2 (724.8 eV) indicated the Fe oxidation state in the

370

adsorbent was +3 (Yang et al., 2018). After the adsorption of As(III) or simultaneous

371

adsorption of As(III) and Cd(II), a significant decrease of the Fe 2p 3/2 spectra

372

intensity was observed, suggesting the strong interactions between As and Fe phase

373

(Zhang et al., 2005). While after reaction with single Cd(II), the Fe 2p 3/2 spectra

374

intensity changed slightly. That means Fe species in the CMZF adsorbent mainly

375

perform as an adsorbent for As. Compared with Fe 2p, other metal spectra like Zn 2p

376

and Mg 1s changed inconspicuously.

AC C

EP

TE D

368

377

At the last as depicted in Fig. 5d, the high resolution scans of O1s spectra could

378

be deconvoluted into three overlapped peaks at around 529.6, 530.4 and 531.7 eV 18

ACCEPTED MANUSCRIPT corresponding to oxide oxygen (M-O), hydroxyl groups (-OH) and adsorbed water

380

(H2O) respectively (Li et al., 2010). After adsorption, the total O1s, M-O and H2O

381

spectra intensity increased obviously, while a significant intensity decrease was

382

observed in -OH. Besides, the peak area ratio of -OH group decreased obviously from

383

38.5% to 27.9% (As (III)), 21.6% (Cd(II)) and 24.6% (As(III) and Cd(II))

384

respectively, By contrast, the peak area ratio of M-O increased signally from 25.3% to

385

37%, 35.5% and 38.9 respectively. All the results implying several -OH has been

386

replaced by As or Cd during the adsorption process and inner-sphere surface

387

complexes were subsequently formed.

M AN U

SC

RI PT

379

388 389

3.3.2 Identification of oxidant for As(III)

It is well known that the process of photocatalytic oxidation for As(III) involves

391

diverse active species, such as photo-generated holes (h+), hydroxyl radicals ( OH)

392

and singlet oxygen (1O2). Electron paramagnetic resonance (EPR) was employed for

393

radical detection and the results was depicted in Fig. S11. The 3-line TEMP-1O2

394

adducts EPR spectra with equal intensities (special hyperfine coupling constants of

395

αN=16.9G (Li et al., 2017)) in the CMZF/light system was captured after 5min

396

irradiation, revealing that 1O2 was produced as the ROS during photocatalysis process.

397

Additionally, both energy transfer and radical reaction of superoxide anion ( O2- )

398

could produce 1O2 (Zhang et al., 2018b; Bai et al., 2019), thus

399

involved in the CMZF/Light system (Eq. (5)). Unfortunately, other primary oxidizing

AC C

EP

TE D

390

19

O2- should be

ACCEPTED MANUSCRIPT radicals was not detected during EPR analyses, which could be the reason of low

401

intensity. Therefore, it is concluded that the main oxidant in the CMZF/light system

402

were the h+ and 1O2, which resulted in the effective oxidization reaction of As(III) to

403

As(V) described in the Eqs. (4) and (7).

404

CMZF + hv → e- + h+

405

h+ + As (III) → As (IV)→ As (V)

406

e- + O2 →

(4)

SC

O2-

M AN U

1

O2 + As (III) → As (IV)→ As (V)

409 410

(3)

O2- + h+ → 1O2

407 408

RI PT

400

(5) (6) (7)

3.3.3 Surface characterization using XRD and mapping images. XRD data and Element mapping images of CMZF after adsorption were also

412

obtained to better understanding the removal mechanism. As depicted in Fig. 6a, after

413

adsorption of As(III), three main characteristic XRD peaks assigned to (003), (006),

414

(009) of layered double hydroxides was found with layer distance of 0.79nm,

415

indicating the reconstruction of the interlayer area. Neutral or negative charged groups

416

like H3AsO3, H2O, H2AsO4- and CO32- will be adsorbed and exchanged into the

417

interlayer by positive charged metal octahedral sheets. The SEM images of CMZF

418

after As(III) treatment became more rough on the surface compared with that before

419

adsorption in a sheet structure morphology. The mapping imagines of All metals

420

and C were homodisperse on the whole area, suggesting As uniformly coordinated

AC C

EP

TE D

411

20

As

ACCEPTED MANUSCRIPT 421

with -OH groups. After treatment of Cd(II) (Fig. 6b), the XRD data showed a series of

423

characteristic peaks of CdCO3, which was in agreement with the XPS analysis of C1s

424

(Fig. 5b). From SEM image we can see the square bulks appeared and destroyed the

425

sheet morphology of CMZF. Mapping images showed an intensive electron density of

426

Cd and C on the bulk area, further proved the formation of CdCO3 crystal. The

427

electron density of Mg in the bulk area was higher than that of Zn or Fe, indicating

428

CdCO3 mainly combine with Mg phase which agree with the former results (Section

429

3.2.1). The intensive and sharp peaks

430

C(Cd)=0.1µmol/L) indicating the strong concentration process of Cd(II) give rise to

431

the outstanding removal efficiency at low concentration.

M AN U

SC

RI PT

422

of CdCO3 crystal (Ksp=1X10-12,

Fig. 6c presented the XRD and mapping images after adsorption of Cd(II) and

433

As(III). The XRD data shown only the (012) characteristic peak of CdCO3. And the

434

SEM image shown a homogeneous sheet layer rather than the bulked CdCO3. It could

435

be explained as follow

436

exchanged into the interlayer owning to the positive charged octahedral sheets of

437

CMZF, and (ii) As(III) will occupy the interlayer area therefore prevent the

438

agglomeration of CdCO3 into well crystallographic bulk at some extent, thus (iii) the

439

isolated CdCO3 only preferentially orientated to the (012) crystal face and growth to

440

the nanocrystals CdCO3 in the surface or interlayer area of CMZF without destroy the

441

sheet structure. The mapping images of all metals, Cd and As are uniform

EP

TE D

432

AC C

(i) first, in the binary system, As(III) was easier to be

21

ACCEPTED MANUSCRIPT 442

homodisperse on the surface of CMZF, suggesting the symmetrically multilayer

443

complexes are formed on the -OH sites. From all the mechanism analysis, the removal mechanisms and interactions of

445

As(III) and Cd(II) were a series process coupled by (i) photooxidation, (ii)

446

precipitation and (iii) adsorption. Particularly, for photooxidation process, As(III) will

447

first be adsorbed onto the surface of CMZF, then acquired two electrons by generated

448

holes (h+) or ROS (1O2, O2-) under irradiation and to be oxidated into less toxic

449

As(V), the oxidative formed As(V) will keep stay on the CMZF surface or go into the

450

bulk solution based on the concentration difference on the solid-liquid interface. For

451

precipitation process, Cd(II) will be attracted by the negative charged CO32- anions on

452

the surface or in the interlayer of CMZF, then rapidly be precipitated to the CdCO3

453

crystal. The dissociative As(III) or As(V) could regulate the agglomerated bulk

454

CdCO3 into the nano CdCO3 and fixed it in the interlayer of CMZF. And for the

455

adsorption process, As(III) or oxidative formed As(V) and residual Cd(II) will be

456

specifically adsorbed by the CMZF adsorbent and coordinated by the -OH groups to

457

form inner-sphere complexes in a combined multilayer, where the negative charged

458

As(V) will provide shielding effect to balance the electrical force among Cd(II), and

459

the coordinated deprotonated As(V) will also play a role as anion bridging to enhance

460

the attraction to Cd(II). In return, Cd(II) could enhance the As(III) adsorption by

461

formation of the ternary surface complexation or coordination and enhanced hydrogen

462

bond. All these mechanisms and synergistic effects qualified the ability of CMZF to

AC C

EP

TE D

M AN U

SC

RI PT

444

22

ACCEPTED MANUSCRIPT 463

deep remove As and Cd in trace concentration level. The summary schematic diagram

464

of removal mechanism was illustrated in Fig. 7.

465 4. Conclusion

RI PT

466

A novel nanostructured CMZF adsorbent was synthesized for effective arsenite

468

and cadmium deep removal. The developed material showed a significant uptake rate

469

for both As(III) and Cd(II) (>99.7%) in low concentration level. The coupled process of

470

photooxidation and adsorption account for the strong removal of As(III), the fast

471

precipitation of CdCO3 and adsorption process is the reason for successful deep

472

removal of Cd(II). The results of the kinetic and isotherm experiment indicated that the

473

light illumination could oxidize As(III) specie to As(V) and enhance the removal of

474

both As(III) and Cd(II) on the water/CMZF interface, where the oxidative formed As(V)

475

could further enhance Cd(II) adsorption by anion bridging and shielding effect. In

476

return, Cd(II) strengthened the As(III) adsorption by formation of the ternary surface

477

complexation or coordination and enhanced hydrogen bond. The effect of ionic

478

strength and Zeta potential measurements results confirmed that both As(III) and Cd(II)

479

were coordinated by CMZF via forming inner-sphere complexes. This work has

480

provided a promising material for the efficient simultaneous deep elimination of

481

environmental neutral and charged inorganic pollutants in practical water treatment

482

application.

483

.

AC C

EP

TE D

M AN U

SC

467

23

ACCEPTED MANUSCRIPT 484

Acknowledgments The authors appreciate financial support from the National Key Research and

486

Development Program of China (2017YFD0801000), the National Natural Science

487

Foundation of China (Grant Nos. 41673092, 41472038), the Science and Technology

488

Plan of Guangdong Province, China (No. 2014A020216002, 2016B020242004),

489

Guangdong special support program for millions of leading engineering talents (No.

490

201626011) and the Science and Technology Program of Guangzhou, China (No.

491

201604020064).

M AN U

SC

RI PT

485

492 493

References:

494

Bai, Y., Shi, X., Wang, P., Wnag, L., Zhang, K., Zhou, Y., Xie, H., Wang, J., Ye, L., 2019. BiOBrxI1−

TE D

x/BiOBr heterostructure engineering for efficient molecular oxygen activation. CHEM ENG J 356, 34-42.

Bouaziz, Z., Soussan, L., Janot, J., Jaber, M., Amara, A.B.H., Balme, S., 2018. Dual role of layered double hydroxide nanocomposites on antibacterial activity and degradation of tetracycline and oxytetracyline. CHEMOSPHERE 206, 175-183.

EP

Chen, L., Zhou, S., Shi, Y., Wang, C., Li, B., Li, Y., Wu, S., 2018. Heavy metals in food crops, soil, andwater in the Lihe River Watershed of the Taihu Region and their potential health risks when ingested. SCI TOTAL ENVIRON 615, 141-149. Chen, M., Wu, P., Yu, L., Liu, S., Ruan, B., Hu, H., Zhu, N., Lin, Z., 2017. FeOOH-loaded MnO 2

AC C

495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515

nano-composite: An efficient emergency material for thallium pollution incident. J ENVIRON MANAGE 192, 31-38.

Esposito, G., Meloni, D., Abete, M.C., Colombero, G., Mantia, M., Pastorino, P., Prearo, M., Pais, A., Antuofermo, E., Squadrone, S., 2018. The bivalve Ruditapes decussatus: A biomonitor of trace elements pollution in Sardinian coastal lagoons (Italy). ENVIRON POLLUT 242, 1720-1728. Fan, G., Li, F., Evans, D.G., Duan, X., 2014. Catalytic applications of layered double hydroxides: recent advances and perspectives. CHEM SOC REV 43, 74-766. Genc-Fuhrman, H., Mikkelsen, P.S., Ledin, A., 2016. Simultaneous removal of As, Cd, Cr, Cu, Ni and Zn from stormwater using high-efficiency industrial sorbents: Effect of pH, contact time and humic acid. SCI TOTAL ENVIRON 566, 76-85. Goldberg, S., Johnston, C.T., 2001. Mechanisms of arsenic adsorption on amorphous oxides evaluated 24

ACCEPTED MANUSCRIPT using macroscopic measurements, vibrational spectroscopy, and surface complexation modeling. J COLLOID INTERF SCI 234, 204-216. González, M.A., Pavlovic, I., Barriga, C., 2015. Cu(II), Pb(II) and Cd(II) sorption on different layered double hydroxides. A kinetic and thermodynamic study and competing factors. CHEM ENG J 269, 221-228. Huang, J., Li, H., Zeng, G., Shi, L., Gu, Y., Shi, Y., Tang, B., Li, X., 2018. Removal of Cd(II) by MEUF-FF with anionic-nonionic mixture at low concentration. SEP PURIF TECHNOL 207, 199-205.

RI PT

Irani, M., Ismail, H., Ahmad, Z., Fan, M., 2015. Synthesis of linear low-density polyethylene-g-poly (acrylic acid)-co-starch/organo-montmorillonite hydrogel composite as an adsorbent for removal of Pb(II) from aqueous solutions. J ENVIRON SCI-CHINA 27, 9-20.

Kang, D., Yu, X., Tong, S., Ge, M., Zuo, J., Cao, C., Song, W., 2013. Performance and mechanism of Mg/Fe layered double hydroxides for fluoride and arsenate removal from aqueous solution. CHEM ENG

SC

J 228, 731-740.

Kim, J., Kim, J., 2014. Arsenite Oxidation-Enhanced Photocatalytic Degradation of Phenolic Pollutants on Platinized TiO2. ENVIRON SCI TECHNOL 48, 13384-13391.

M AN U

Lee, S., Tanaka, M., Takahashi, Y., Kim, K., 2018. Enhanced adsorption of arsenate and antimonate by calcined Mg/Al layered double hydroxide: Investigation of comparative adsorption Check for mechanism by surface characterization. CHEMOSPHERE 211, 903-911.

Li, D., Duan, X., Sun, H., Kang, J., Zhang, H., Tade, M.O., Wang, S., 2017. Facile synthesis of nitrogen-doped graphene via low-temperature pyrolysis: The effects of precursors and annealing ambience on metal-free catalytic oxidation. CARBON 115, 649-658.

Li, X., Li, Z., Lin, C., Bi, X., Liu, J., Feng, X., Zhang, H., Chen, J., Wu, T., 2018. Health risks of heavy

TE D

metal exposure through vegetable consumption near a large-scale Pb/Zn smelter in central China. ECOTOX ENVIRON SAFE 161, 99-110.

Li, Z., Deng, S., Yu, G., Huang, J., Lim, V.C., 2010. As(V) and As(III) removal from water by a Ce-Ti oxide adsorbent: Behavior and mechanism. CHEM ENG J 161, 106-113. Li, Z., Wang, L., Meng, J., Liu, X., Xu, J., Wang, F., Brookes, P., 2018. Zeolite-supported nanoscale

EP

zero-valent iron: New findings on simultaneous adsorption of Cd(II), Pb(II), and As(III) in aqueous solution and soil. J HAZARD MATER 344, 1-11. Lin, L., Liu, J., Lv, J., Shen, S., Wu, X., Wu, D., Qu, Y., Zheng, W., Lai, F., 2017. Correlation between native defects and morphological, structural and optical properties of ZnO nanostructures. J ALLOY

AC C

516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557

COMPD 695, 1523-1527.

Liu, X., Liu, W., Rong, W., Li, J., Lin, Z., 2018. Surface defects enhance the adsorption affinityband selectivity of Mg(OH)2 towards As(V) and Cr(VI) oxyanions: a combined theoretical and experimental study. Environmental Science Nano 5, 2570-2578. Lofrano, G., Carotenuto, M., Libralato, G., Domingos, R.F., Markus, A., Dini, L., Gautam, R.K., Baldantoni, D., Rossi, M., Sharma, S.K., Chattopadhyaya, M.C., Giugni, M., Meric, S., 2016. Polymer functionalized nanocomposites for metals removal from water and wastewater: An overview. WATER RES 92, 22-37. López-Muñoz, M.J., Arencibia, A., Segura, Y., Raez, J.M., 2017. Removal of As(III) from aqueous solutions through simultaneous photocatalytic oxidation and adsorption by TiO 2 and zero-valent iron. CATAL TODAY 280, 149-154. 25

ACCEPTED MANUSCRIPT Lu, H., Zhu, Z., Zhang, H., Zhu, J., Qiu, Y., Zhu, L., Küppers, S., 2016. Fenton-Like Catalysis and Oxidation/Adsorption Performances of Acetaminophen and Arsenic Pollutants in Water on a Multimetal Cu

Zn

Fe-LDH. ACS APPL MATER INTER 8, 25343-25352.

M., S., T. C., S.G., 2017. Enhanced nonlinear optical absorption and optical limiting properties of superparamagnetic spinel zinc ferrite decorated reduced graphene oxide nanostructures. APPL SURF SCI 392, 904-911. McBride, M.B., 1997. A critique of diffuse double layer models applied to colloid and surface chemistry.

RI PT

CLAY CLAY MINER 45, 598-608.

Mueller, K., Ciminelli, V.S.T., Dantas, M.S.S., Willscher, S., 2010. A comparative study of As(III) and As(V) in aqueous solutions and adsorbed on iron oxy-hydroxides by Raman spectroscopy. WATER RES 44, 5660-5672.

Parida, K.M., Mohapatra, L., 2012. Carbonate intercalated Zn/Fe layered double hydroxide: A novel

SC

photocatalyst for the enhanced photo degradation of azo dyes. CHEM ENG J 179, 131-139.

Pawar, R.R., Lalhmunsiama, Kim, M., Kim, J., Hong, S., Sawant, S.Y., Lee, S.M., 2018. Efficient removal of hazardous lead, cadmium, and arsenic from aqueous environment by iron oxide modified

M AN U

clay-activated carbon composite beads. APPL CLAY SCI 162, 339-350.

Rahman, M.T., Kameda, T., Kumagai, S., Yoshioka, T., 2018. A novel method to delaminate nitrate-intercalated Mg-Al layered double hydroxides in water and application in heavy metals removal from waste water. CHEMOSPHERE 203, 281-290.

Rehman, S., Adil, A., Shaikh, A.J., Shah, J.A., Arshad, M., Ali, M.A., Bilal, M., 2018. Role of sorption energy and chemisorption in batch methylene blue and Cu2+ adsorption by novel thuja cone carbon in binary component system: linear and nonlinear modeling. ENVIRON SCI POLLUT R 25, 31579-31592.

TE D

Ren, X., Wu, Q., Xu, H., Shao, D., Tan, X., Shi, W., Chen, C., Li, J., Chai, Z., Hayat, T., Wang, X., 2016. New Insight into GO, Cadmium(II), Phosphate Interaction and Its Role in GO Colloidal Behavior. ENVIRON SCI TECHNOL 50, 9361-9369.

Singh, B., Fang, Y., Cowie, B.C.C., Thomsen, L., 2014. NEXAFS and XPS characterisation of carbon functional groups of fresh and aged biochars. ORG GEOCHEM 77, 1-10.

EP

Sun, T., Zhao, Z., Liang, Z., Liu, J., Shi, W., Cui, F., 2017. Efficient removal of arsenite through photocatalytic oxidation and adsorption by ZrO 2 -Fe 3 O 4 magnetic nanoparticles. APPL SURF SCI 416, 656-665.

Sun, T., Zhao, Z., Liang, Z., Liu, J., Shi, W., Cui, F., 2018. Efficient degradation of p-arsanilic acid with

AC C

558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599

arsenic adsorption by magnetic CuO-Fe3O4 nanoparticles under visible light irradiation. CHEM ENG J 334, 1527-1536.

Türk, T., Alp, İ., Deveci, H., 2009. Adsorption of As(V) from water using Mg

Fe-based hydrotalcite

(FeHT). J HAZARD MATER 171, 665-670. Vaiano, V., Iervolino, G., Rizzo, L., 2018. Cu-doped ZnO as efficient photocatalyst for the oxidation of arsenite to arsenate under visible light. Applied Catalysis B: Environmental 238, 471-479. Vaiano, V., Iervolino, G., Sannino, D., Rizzo, L., Sarno, G., Farina, A., 2014. Enhanced photocatalytic oxidation of arsenite to arsenate in water solutions by a new catalyst based on MoOx supported on TiO2. Applied Catalysis B: Environmental 160-161, 247-253. Wang, D., Wu, J., Bai, D., Wang, R., Yao, F., Xu, S., 2017. Mesoporous spinel ferrite composite derived from a ternary MgZnFe-layered double hydroxide precursor for lithium storage. J ALLOY COMPD 726, 26

ACCEPTED MANUSCRIPT 306-314. Wang, Q., O Hare, D., 2012. Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets. CHEM REV 112, 4124-4155. Wasana, H.M.S., Perera, G.D.R.K., Gunawardena, P.D.S., Fernando, P.S., Bandara, J., 2017. WHO water quality standards Vs Synergic effect(s) of fluoride, heavy metals and hardness in drinking water on kidney tissues. SCI REP-UK 7. Wu, J., Huang, D., Liu, X., Meng, J., Tang, C., Xu, J., 2018. Remediation of As(III) and Cd(II)

RI PT

co-contamination and its mechanism in aqueous systems by a novel calcium-based magnetic biochar. J HAZARD MATER 348, 10-19.

Xie, L., Liu, P., Zheng, Z., Weng, S., Huang, J., 2016. Morphology engineering of V 2 O 5 /TiO 2 nanocomposites with enhanced visible light-driven photofunctions for arsenic removal. Applied Catalysis B: Environmental 184, 347-354.

SC

Yan, H., Chen, Q., Liu, J., Feng, Y., Shih, K., 2018. Phosphorus recovery through adsorption by layered double hydroxide nano-composites and transfer into a struvite-like fertilizer. WATER RES 145, 721-730. Yan, L., Huang, Y., Cui, J., Jing, C., 2015. Simultaneous As(III) and Cd removal from copper smelting

M AN U

wastewater using granular TiO2 columns. WATER RES 68, 572-579.

Yang, S., Wu, P., Ye, Q., Li, W., Chen, M., Zhu, N., 2018. Efficient catalytic degradation of bisphenol A by novel Fe0- vermiculite composite in photo-Fenton system: Mechanism and effect of iron oxide shell. CHEMOSPHERE 208, 335-342.

Yoon, K., Cho, D., Tsang, D.C.W., Bolan, N., Rinklebe, J., Song, H., 2017. Fabrication of engineered biochar from paper mill sludge and its application into removal of arsenic and cadmium in acidic water. BIORESOURCE TECHNOL 246, 69-75.

TE D

Yu, H., Ding, X., Li, F., Wang, X., Zhang, S., Yi, J., Liu, C., Xu, X., Wang, Q., 2016. The availabilities of arsenic and cadmium in rice paddy fields from a mining area: The role of soil extractable and plant silicon. ENVIRON POLLUT 215, 258-265.

Zhang, G., Liu, F., Liu, H., Qu, J., Liu, R., 2014. Respective Role of Fe and Mn Oxide Contents for Arsenic Sorption in Iron and Manganese Binary Oxide: An X-ray Absorption Spectroscopy Investigation.

EP

ENVIRON SCI TECHNOL 48, 10316-10322.

Zhang, W., Zhang, G., Liu, C., Li, J., Zheng, T., Ma, J., Wang, L., Jiang, J., Zhai, X., 2018a. Enhanced removal of arsenite and arsenate by a multifunctional Fe-Ti-Mn composite oxide: Photooxidation, oxidation and adsorption. WATER RES 147, 264-275.

AC C

600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641

Zhang, W., Zhang, G., Liu, C., Li, J., Zheng, T., Ma, J., Wang, L., Jiang, J., Zhai, X., 2018b. Enhanced removal of arsenite and arsenate by a multifunctional Fe-Ti-Mn composite oxide: Photooxidation, oxidation and adsorption. WATER RES 147, 264-275. Zhang, Y., Yang, M., Dou, X.M., He, H., Wang, D.S., 2005. Arsenate adsorption on an Fe-Ce bimetal oxide adsorbent: Role of surface properties. ENVIRON SCI TECHNOL 39, 7246-7253. Zhang, Y., Zhou, J., Feng, Q., Chen, X., Hu, Z., 2018. Visible light photocatalytic degradation of MB using UiO-66/g-C3N4 heterojunction nanocatalyst. CHEMOSPHERE 212, 523-532. Zhu, C., Liu, F., Xu, C., Gao, J., Chen, D., Li, A., 2015. Enhanced removal of Cu(II) and Ni(II) from saline solution by novel dual-primary-amine chelating resin based on anion-synergism. J HAZARD MATER 287, 234-242. Zhu, C., Liu, F., Zhang, Y., Wei, M., Zhang, X., Ling, C., Li, A., 2016. Nitrogen-doped chitosan-Fe(III) 27

ACCEPTED MANUSCRIPT composite as a dual-functional material for synergistically enhanced co-removal of Cu(II) and Cr(VI) based on adsorption and redox. CHEM ENG J 306, 579-587. Zhu, J., Zhu, Z., Zhang, H., Lu, H., Zhang, W., Qiu, Y., Zhu, L., Küppers, S., 2018. Calcined layered double hydroxides/reduced graphene oxide composites with improved photocatalytic degradation of paracetamol and efficient oxidation-adsorption of As(III). Applied Catalysis B: Environmental 225,

EP

TE D

M AN U

SC

RI PT

550-562.

AC C

642 643 644 645 646 647 648 649

28

ACCEPTED MANUSCRIPT Figures Fig. 1 SEM images of (a) MZF LDH, (b) CMZF; TEM images (c) MZF LDH (d) CMZF and Element mapping images (e, f) of MZF LDH

CMZF 0.5 g/L and Temperature 30±1 ℃).

RI PT

Fig. 2 Effects of pH and irradiation on CMZF adsorbent (Conditions: As(III) 1mg/L, Cd(II) 1mg/L,

Fig. 3 Effect of reaction time and kinetic study of As and Cd on CMZF adsorbent (Conditions:

SC

As(III) 1mg/L, As( )1mg/L Cd(II) 1mg/L, CMZF 0.5 g/L CMZF, Temperature 30±1 ℃and pH

M AN U

= 6).

Fig. 4 Effect of initial concentration and isotherm study of As and Cd on CMZF adsorbent (Conditions: As(III) and As( ) 1-100mg/L, Cd(II) 1-260mg/L, CMZF 0.5 g/L, reaction time 12h, Temperature 30±1 ℃ and pH = 6).

TE D

Fig. 5 XPS spectra of (a) As 3d, (b) C 1s, (c) Fe 2p and (d) O 1s on the CMZF adsorbent surface before and after adsorption.

As and Cd.

EP

Fig. 6 XRD and Element mapping images of CMZF after the adsorption of (a)As, (b) Cd and (c)

AC C

Fig. 7 Schematic diagram of the arsenic and cadmium removal mechanism by CMZF adsorbent.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 1 SEM images of (a) MZF LDH, (b) CMZF; TEM images (c) MZF LDH (d) CMZF and Element mapping images (e, f) of MZF LDH.

Fig. 2 Effects of pH and irradiation on CMZF adsorbent (Conditions: As(III) 1mg/L, Cd(II) 1mg/L, CMZF 0.5 g/L, reaction time 6h and Temperature 30±1 ℃).

ACCEPTED MANUSCRIPT

As concentration (ug/L)

10

60

90

120

150

20 15 10

100 20

40

60

80

10 0

1 20

Ti me (m in)

As(III) in the dark As(III) in the light As(V) in the dark As(V) in the light

10

10

1

0

180

30

60

90

120

150

180

Time (min)

10

1

Cd(II) single Cd(II) with As(III) in the dark Cd(II) with As(III) in the light

SC

100

d

1000

Cd Concentration (ug/L)

As(III) single in the dark As(III) single in the light As(III) with Cd(II) in the light As(III) with Cd(II) in the dark

100

M AN U

As Concentration (ug/L)

c

25

0

Time (min) 1000

30

0

1 30

35

5

100

1 0

1000

in th e light in th e dark

40

RI PT

100

45

As(? ) concentration (ug/L)

1000

As(III) in the dark As(V) in the dark

As Concentration (ug/L)

50

b

1000

A s(? ) concentra tion (ug/L)

a

10

1

0

20

40

60

80

100

120

Time (min)

140

160

180

0

30

60

90

120

150

180

Time (min)

TE D

Fig. 3 Effect of reaction time and kinetic study of As and Cd on CMZF adsorbent (Conditions:

AC C

EP

As(III) 1mg/L, As( )1mg/L, Cd(II) 1mg/L, CMZF 0.5 g/L, Temperature 30±1 ℃and pH = 6).

ACCEPTED MANUSCRIPT 100

a

b

As(III)

80

As(V)

80 60

Qe (mg/g)

40

As(III) single As(III) with Cd(II) Langmuir Freundlich

20

40

As(V) single As(V) with Cd(II) Langmuir Freundlich

20

0

0 0

10

20

30

40

50

60

70

80

0

10

20

30

Ce (mg/g)

c

d 200

250

50

60

70

80

Qe (mg/g)

100

0

150

100

M AN U

Cd(II) single Cd(II) with As(III) Langmuir Freundlich

SC

200

150

Qe (mg/g)

40

Ce (mg/g)

250

50

RI PT

Qe (mg/g)

60

Cd(II) single Cd(II) with As(V) Langmuir Freundlich

50

0

0

20

40

60

80

100

120

Ce (mg/g)

140

160

180

0

20

40

60

80

100

120

140

160

Ce (mg/g)

Fig. 4 Effect of initial concentration and isotherm study of As and Cd on CMZF adsorbent

TE D

(Conditions: As(III) and As( ) 1-100mg/L, Cd(II) 1-260mg/L, CMZF 0.5 g/L, reaction time 12h,

AC C

EP

Temperature 30±1 ℃ and pH = 6).

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 5 XPS spectra of (a) O 1s, (b) C 1s, (c) Fe 2p and (d) As 3d on the CMZF adsorbent surface

AC C

EP

TE D

before and after adsorption.

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 6 XRD and Element mapping images of CMZF after the adsorption of (a)As, (b) Cd, (c) As

AC C

EP

and Cd.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 7 Schematic diagram of the arsenite and cadmium removal mechanism by CMZF adsorbent.

ACCEPTED MANUSCRIPT Highlights


Multiple functions of photooxidation, precipitation and adsorption were integrated into CMZF nanoparticle. exhibits

excellent

synchronous

concentration As(III) and Cd(II).


ability

towards

trace

The synergistic interaction among As(III) molecule, As (V) anion and Cd(II) cation in removal process was proposed.

M AN U

As(III) and Cd(II) in actual water were removed simultaneously and efficiently to

EP

TE D

satisfy drinking water provision.

AC C




removal

RI PT

CMZF

SC