Removal of Organoarsenic with Ferrate and Ferrate Resultant

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Remediation and Control Technologies

Removal of Organoarsenic with Ferrate and Ferrate Resultant Nanoparticles: Oxidation and Adsorption Tao Yang, Lu Wang, Yu-Lei Liu, Jin Jiang, Zhuangsong Huang, Su-yan Pang, Haijun Cheng, Dawen Gao, and Jun Ma Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 22, 2018

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Environmental Science & Technology

1

Removal of Organoarsenic with Ferrate and Ferrate

2

Resultant Nanoparticles: Oxidation and Adsorption

3 4

Tao Yang1, Lu Wang1 ， *, Yulei Liu2, Jin Jiang1, Zhuangsong Huang1, Su-Yan Pang3,

5

Haijun Cheng1, Dawen Gao1, Jun Ma1，**

6

7

1

State Key Laboratory of Urban Water Resource and Environment, School of

8

Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin

9

150090, China

10

2

11

Technology, Dongguan 523808, China

12 13

Technology R & D Center for Environmental Engineering, Dongguan University of

3

School of Municipal and Environmental Engineering, Jilin Jianzhu University,

Changchun 130118, China

14

15

*Corresponding

16

*

17

**

authors:

Lu Wang, Phone/ Fax: 86 451 86283010; e-mail: [email protected]; Jun Ma, Phone/ Fax: 86 451 86283010; e-mail: [email protected];

18 1

ACS Paragon Plus Environment


19

Abstract

20

Many investigations focused on the capacity of ferrate for the oxidation of organic

21

pollutant or adsorption of hazardous species, while little attention has been paid on the

22

effect of ferrate resultant nanoparticles for the removal of organics. Removing organics

23

could improve microbiological stability of treated water and control the formation of

24

disinfection by-products in following treatment procedures. Herein, we studied ferrate

25

oxidation of p-arsanilic acid (p-ASA), an extensively used organoarsenic feed additive.

26

p-ASA was oxidized into As(V), p-aminophenol (p-AP), and nitarsone in the reaction

27

process. The released As(V) could be eliminated by in situ formed ferric (oxyhydr)

28

oxides through surface adsorption, while p-AP can be further oxidized into

29

4,4'-(diazene-1,2-diyl) diphenol, p-nitrophenol, and NO3-. Nitarsone is resistant to ferrate

30

oxidation, but mostly adsorbed (> 85%) by ferrate resultant ferric (oxyhydr) oxides.

31

Ferrate oxidation (ferrate/p-ASA = 20:1) eliminated 18% of total organic carbon (TOC),

32

while ferrate resultant particles removed 40% of TOC in the system. TOC removal

33

efficiency is 1.6 to 38 times higher in ferrate treatment group than those in O3, HClO, and

34

permanganate treatment groups. Besides ferrate oxidation, adsorption of organic

35

pollutants with ferrate resultant nanoparticles could also be an effective method for water

36

treatment and environmental remediation.

37 38

Keywords: Ferrate; Oxidation; Adsorption; p-Arsanilic acid; Arsenate 2


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39

1. Introduction

40

Aromatic

organoarsenic

compounds,

such

as

p-ASA

and

41

3-nitro-4-hydroxypheyl-arsonic acid, were used as feed additive and veterinary drug to

42

promote growth of livestock and control parasitic diseases 1. Accompanied with surging

43

demand for meat products, consumption of aromatic organoarsenic compounds is

44

increasing. Studies estimated that over thousands of tons of aromatic organoarsenic

45

compounds were released into environment through solid waste and wastewater from

46

swine and poultry farms

47

and 0.5 to 5000 μg L–1 in soil and water in some regions of China 5. Although aromatic

48

organoarsenic compounds are not highly toxic, they would be transformed into

49

carcinogenic and highly mobile inorganic As species [As(III) and As(V)]

50

the pollution of aquatic systems and threating the safety of ecosystems.

2-4,

and their concentrations ranged from 0.2 to 1000 μg kg–1,

6, 7,

leading to

51

p-ASA is one of the largely used aromatic organoarsenic compounds, and many

52

studies explored the removal of p-ASA. Under ultraviolet-C light (254 nm) irradiation

53

without dissolved oxygen, p-ASA removal rate ranged from 0.077 μM min-1 at pH 1.0 to

54

3.78 μM min-1 at pH 11.0 8. When dissolved oxygen exists, hydroxyl radical and singlet

55

oxygen would form and enhance the removal of p-ASA

56

photo degradation system, pseudo first order reaction rate constants increased to 36.4 ×

57

10−3 min−1 at pH 2.0

58

efficient for the degradation of p-ASA. Under optimized condition, over 99% of p-ASA

11.

9, 10.

After H2O2 was added into

Compared with photo-degradation, chemical oxidation is more

3



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59

(10 mg-As L−1) would be oxidized to As(V) within 30 min at pH 4.0 in Fenton reaction,

60

and the newly formed As(V) can be subsequently removed by iron oxides

61

adsorbents such as metal-organic framework 13-15 and iron-based metal oxide particle 16-20

62

could remove p-ASA in polluted source water and inhibit the release of inorganic As

63

species. However, physical adsorption mainly relies on electrostatic attraction and pore

64

filling processes, and the adsorption equilibrium time is normally longer than 5 h.

65

Adsorption process would be negatively impacted by background constituents in natural

66

waters. Previous studies also revealed that compared with those with As(V), adsorption

67

constants of p-ASA and 3-nitro-4-hydroxypheyl-arsonic acid with Fe oxides or Al oxides

68

were lower 17, 21, 22. Organic moiety of p-ASA may negatively influence the complexation

69

of organoarenicals with metal oxides. Hence, transform p-ASA to As(V) may improve

70

the overall As-removal efficiency in polluted water.

12.

Besides,

71

Ferrate [Fe(VI)] draws extensive interest as an environmentally friendly oxidant 23, 24.

72

It is highly reactive with organics containing nitrogen, sulphur, and electron rich moieties

73

(such as unsaturated bonds and aromatic ring) 25-28. Oxygen atoms were transferred from

74

ferrate to target pollutants with the formation of hydroxylation products, while ferrate

75

was simultaneously reduced into ferric (oxyhydr) oxides (Fe2O3, FeOOH, and

76

armouphous ferric). These in situ formed ferric (oxyhydr) oxides are highly dispersed,

77

small in size (nanoparticle), and have abundant hydroxylation group. They may interact

78

with oxidation products through the function of chemical bonds and hydrogen bond and 4


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79

adsorb them. However, previous investigations seldom examine this process and study

80

the effectiveness of ferrate resultant particles on removal of organics. Relevant

81

exploration would provide a new perspective for understanding the potential of ferrate

82

treatment on pollutants control.

83

The objective of this study is to evaluate the effects of ferrate on p-ASA oxidation

84

and total-As control, and explore the effectiveness of ferrate resultant particles for the

85

removal of organics. Firstly, the reaction kinetics were determined in buffered waters

86

from pH 6.0 to 10.0. The variation of As species in the reaction process was investigated,

87

and removal of total-As and TOC with different dosages of oxidants (HClO,

88

permanganate, ferrate, and O3) was examined. Performance of ferrate oxidation and ferric

89

(oxyhydr) oxides adsorption on the removal of TOC was compared. Effects of natural

90

organic matters, electrolyte ions and solution pH on the oxidation of p-ASA and removal

91

of As species were analyzed subsequently. After that, the reaction mechanism was

92

proposed, and the toxicity of p-ASA oxidation products towards E.coli and P.

93

phosphoreum was evaluated.

94 95

2. Materials and methods

96

2.1 Chemicals and reagents.

97

p-ASA (98% purity) was purchased from Tokyo Chemical Industry (TCI, Japan) and

98

dissolved in pure water as stock solution (1 mM). Suwannee River Humic Acids (SRHA) 5



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99

(2S101H) was purchased from International Humic Substances Society. Other chemicals

100

were of analytical grade and directly used as received. Potassium ferrate (K2FeO4) was

101

prepared according to previously described method 29, 30. Detailed preparation procedures

102

are listed in supporting information (SI, Text S1). In experiment, K2FeO4 powder

103

(purity > 90 %) was dissolved in 1mM NaHCO3 (pH = 9.2) as stock solution. Ferrate

104

stock solution was filtered through a hydrophilic acetate fiber membrane of 0.22 μm pore

105

size (Shanghai ANPEL, China) and concentration of ferrate was determined with a UV–

106

Visible spectrophotometry at 510 nm (Ɛ510nm = 1150 cm-1M-1)

107

defined amount of K2FeO4 stock solution was swiftly added into the reactors. Preparation

108

of SRHA stock solutions is described in Text S2.

109

2.2 Oxidation experiment

31.

After calculation,

110

Oxidation experiment was carried out in glass beakers equipped with a magnetic

111

stirrer (500 r/min) at 25.0 ± 0.2 °C. In most cases, solution pH was buffered with 20 mM

112

borate buffer. Reactions were started by adding an aliquot of ferrate stock solution

113

(filtered and standardized) to p-ASA solution under rapid mixing condition. At different

114

time intervals, 1.0 mL of the solution was sampled and added into a 2.0 mL vial

115

containing 10 μL of 700 mM hydroxylamine hydrochloride (quenching the reaction).

116

Oxidation kinetics were fitted with second-order reaction rate law [Eq (1)]. Experiments

117

were conducted under pseudo-first-order conditions (concentration of ferrate is in excess

118

to p-ASA, [ferrate]0 = 50 μM, [p-ASA]0 = 5 μM), and concentration changes of ferrate 6


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119


and p-ASA were recorded as a function of reaction time (Eq (1)).

120 121

-d[p-ASA]/dt = kapp[p-ASA][ferrate]total

(1)

Eq (2) shows the integral form of Eq (1), t

122

ln([p-ASA]t/[p-ASA]0) = - kapp∫0[ferrate]dt

(2)

123

Besides ferrate, KMnO4, HClO and O3 were also used for the oxidation of p-ASA. In

124

the experiment, definite amount of KMnO4, HClO or O3 was added into pH-buffered

125

solutions (20 mM borate buffer) containing p-ASA. Solution was sampled at different

126

time intervals. Thiosulfate was used for quenching the residual HClO, and

127

hydroxylamine hydrochloride was used for quenching the residual KMnO4 in the

128

collected samples. Detailed information about the oxidation experiment is presented in

129

Text S3. Reaction kinetics study is described in Text S4. Experiment about the removal

130

profile of As is presented in Text S5.

131

2.3 Toxicity assay

132

Toxicity of p-ASA and its oxidation products towards E. coli was investigated

133

according to the procedures described in previous study 32. We initially investigated the

134

toxicity of 10 μM of p-ASA on E. coli, but no obvious antimicrobial effect was observed.

135

When the p-ASA concentration increased to 2.5 mM, the growth of E. coli was obviously

136

inhibited. In experiment, 2.5 mM of p-ASA reacted with 25 mM of ferrate for an hour.

137

Then the solution was filtered through a sterile hydrophilic acetate fiber membrane of

138

0.45 μm pore size to remove particles and floc. Five test groups were set: control group 7



139

(containing 20 mL LB medium and 100 mL of 20 mM PBS, pH 7.0); ferrate treated

140

p-ASA group (containing 20 mL LB medium and 100 mL sterile reaction solution);

141

p-ASA group (containing 20 mL LB medium, 100 mL sterile deionized water, and 2.5

142

mM of p-ASA); As(III) group (containing 20 mL LB medium, 100 mL sterile deionized

143

water, and 2.5 mM of As(III)); As(V) group (containing 20 mL LB medium, 100 mL

144

sterile deionized water, and 2.5 mM of As(V)). E. coli K12 strain in exponential phase

145

was inoculated into the bottles and maintained at 150 rpm on a shaker (35 ºC). The

146

optical density value of bacterial culture at 600 nm was measured by UV–Visible

147

spectrophotometry.

148

The acute toxicity of p-ASA oxidation products was evaluated by marine luminescent

149

marine bacterium P. phosphoreum (purchased from ShenZhen HuaJu Scientific

150

Instrument Co.,LTD) according to national standard of China GB/T15441-1995 (Water

151

Quality: Determination of the acute toxicity-Luminescent bacteria test). After 15 min of

152

culture (25 ºC), the luminescent intensity of P. phosphoreum was recorded by a

153

microplate reader (SpectraMax M5, Molecular Devices, USA). The inhibition ratio of

154

luminescent intensity was calculated based on a toxicant-free control to reflect the acute

155

toxicity of the solution samples.

156

2.4 Analytical methods

157

p-ASA and nitarsone concentrations were determined with Waters 2695 series

158

high-performance liquid chromatography (HPLC), with UV detection at 254 nm. The 8


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159

concentration of inorganic As species was determined by an inductively coupled plasma

160

mass spectrometer (ICP-MS, NexION 300Q, Perkin-Elmer) with a HPLC for separation.

161

The chemical state of As in p-ASA and the settled solids in the reaction of p-ASA with

162

ferrate is examined by Thermo Fisher (ESCALAB 250Xi) X-ray photoelectron

163

spectrometer (XPS). Fourier transform infrared spectroscopy (FTIR) analysis of the

164

settled solids was conducted on a PerkinElmer Spectrum One FTIR. Solid samples were

165

diluted to a concentration of 2% with IR-grade KBr. FTIR spectra were collected at 4

166

cm-1 resolution in the IR region of 4000 - 400 cm-1 for pure KBr and the samples.

167

High-resolution transmission electron microscope (HR-TEM) samples were prepared by

168

depositing a drop of solution sample onto a 200-mesh carbon film supported by copper

169

grids. TEM samples were analyzed by JEM-2100 transmission electron microscope

170

(JEOL, Japan) at accelerating voltage of 200 kV. TOC content of solution samples was

171

determined by TOC-VCHS (Shimadzu, Kyoto, Japan). Content of NO3- was determined

172

with a DIONEX ICS ion chromatography system. Concentration of p-AP was determined

173

by HPLC at a flow rate 1.0mL/min. The mobile phase was water and methanol (70:30,

174

v/v), and determined at wavelength of 317 nm. Zeta potential of ferric (oxyhydr) oxide

175

was determined by Malvern Zetasizer (Malvern Instruments Ltd., Worcestershire, UK).

176

Mass spectrum analysis was carried out with a high-resolution hybrid quadrupole

177

time-of-flight mass spectrometer (QTOF 5600, AB Sciex, USA) equipped with an

178

electrospray ion (ESI) source. Detailed information is listed in Text S6. 9



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179 180

3. Results and discussion

181

3.1 Ferrate oxidation of p-ASA and reaction stoichiometry

182

Reaction kinetics of p-ASA with ferrate under different pH conditions were initially

183

investigated. When 5 μM of p-ASA reacted with 50 μM of ferrate at pH 6.0, the

184

concentration of residual p-ASA decreased below HPLC detection limit (< 0.05 μM)

185

within 10 s. Over 90% of p-ASA was removed within 1 min in pH 7.0 and 7.5 groups,

186

and the concentration of residual p-ASA decreased below detection limit within 1.5 and

187

10 min, respectively (Figure 1A). When solution pH increased to 8.0, 8.5, and 9.0, time

188

for the removal of over 90% of p-ASA prolonged to 10 min, 30 min, and 40 min,

189

respectively. Ferrate oxidation of p-ASA was pH-dependent, and acidic condition is in

190

favor for the reaction process.

191

Second-order reaction rate law [Eq (1)] was used to study the reaction kinetics. By

192

plotting natural logarithm of p-ASA concentrations with ferrate exposure (∫0[ferrate]dt),

193

reaction kinetics under various pH conditions were obtained (Table S1 and Figure S1). At

194

pH 6.0, the determined kapp value was 8.4 × 103 M-1s-1. As solution pH increased to 7.0,

195

7.5, 8.0, 8.5, 9.0, and 10.0, the kapp values were 2.0 × 103 M-1s-1, 7.1 × 102 M-1s-1, 1.2 ×

196

102 M-1s-1, 2.9 × 10 M-1s-1, 2.1 × 10 M-1s-1, and 2.9 M-1s-1, respectively. Previous studies

197

reported that for ferrate oxidation of As(III), the kapp value is 3.54 × 105 M-1s-1 at pH 8.4;

198

for ferrate oxidation of p-AP, the kapp values are 6.6 × 103 M-1s-1 at pH 7.0 and 7.2 × 103

t

10


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199

M-1s-1 at pH 8.0, respectively

200

of ferrate with As(III) or p-AP is much faster. Chemically, arsenic group, amino group,

201

and benzene ring of p-ASA are electron rich moieties. Electron cloud of these moieties

202

would interact with each other, leading to the formation of π-conjugated system and

203

homogeneity of electron distribution. This would improve the chemical stability of

204

p-ASA and decrease its reactivity with ferrate.

33, 34.

Compared with ferrate oxidation of p-ASA, reaction

205 206

Figure 1. Concentration change of p-ASA (5 μM) in the reaction with ferrate (50 μM) as a function of

207

reaction time under different pH conditions (A); comparison of kapp values of p-ASA with ferrate,

208

HClO, and permanganate [Mn(VII)] (B); stoichiometry of the reaction between ferrate and p-ASA

209

(pH 9.0) ([Fe(VI)]R represents the amount of ferrate reacted with p-ASA, as other part of ferrate

210

would self-decay in water) (C); variation of p-ASA, As(III), As(V), p-AP, nitarsone, and NO3-

211

concentration in the reaction of ferrate with p-ASA (25 μM) (D); variation of total-As (solution

212

samples were filtered with 0.22 μm membrane before detection) and nitarsone (solution samples were

213

acidified with HCl, without filtration) content in the reaction of ferrate (50 μM) with nitarsone (5 μM) 11



214

215

(E).

Ferrate is a diprotic acid [H2FeO4 = HFeO4- + H+, pKa, H2FeO4 = 3.5; HFeO4- = FeO42-

216

+ H+, pKa, HFeO4- = 7.23]

217

9.2) 20. pH dependency of kapp for ferrate with p-ASA could be modeled by eq 3.

218

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35

and p-ASA is a triprotic acid (pKa1 = 1.9; pKa2 = 4.1; pKa3 =

𝑖 = 1,2

𝑘[𝐹𝑒(𝑉𝐼) ― 𝑝 ― 𝐴𝑆𝐴] = ∑𝑗 = 1,2𝑘𝑖,𝑗𝛼𝑖𝛽𝑗

(3)

219

Where αi and βj represent the fractions of different ferrate and p-ASA species

220

respectively, i and j represent the respective different species of ferrate and p-ASA

221

species, and ki,j represents the species-specific second-order rate constants of the

222

reactions for each i and the corresponding j. From pH 6.0 to 10.0, model fitting result is

223

in accordance with the determined rate constants (R2 = 0.998) (Text S4, Figure S2).

224

Based on the results, the calculated k11 [(5.3 ± 0.2) × 105 M-1s-1] is over 200 times higher

225

than k12 [(2.3 ± 0.2) × 103 M-1s-1], which indicates that the reaction of HFeO4- species with

226

deprotonated p-ASA dominants the overall reaction from pH 6.0 to 10.0.

227

Besides ferrate, other oxidants such as chlorine (HClO) and permanganate could also

228

react with p-ASA. The reaction kinetics of p-ASA with HClO and permanganate were

229

determined respectively (Figure 1B). Similar with that of ferrate, permanganate oxidation

230

of p-ASA is pH-dependent and fast under acidic condition. Reaction rates of

231

permanganate with p-ASA decreased from 14.9 M-1s-1 at pH 4.0 to 0.03 M-1s-1 at pH 7.0,

232

4 ~ 5 orders of magnitude lower than that of ferrate with p-ASA under similar pH

233

conditions. At pH 7.0, less than 20% of p-ASA was oxidized by permanganate in 24 h. 12


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234

For the chlorination of p-ASA, profile of rate constants as a function of solution pH is

235

bell-shaped. Rate constants increased from 27.4 M-1s-1 at pH 6.0 to 211.2 M-1s-1 at pH 7.5,

236

and decreased to 74 M-1s-1 at pH 9.0. The pKa value of HOCl is 7.54, and reactivity of

237

HOCl is higher than that of OCl-. This property makes the oxidation ability of HOCl to

238

be the highest at pH 7.54, and dissociation of HOCl results in low rate constants with

239

p-ASA under alkaline condition. Compared with permanganate oxidation and

240

chlorination, ferrate oxidation of p-ASA is the rapidest under circumneutral pH

241

condition.

242

Reaction stoichiometry of p-ASA with ferrate was determined at pH 9.0 (adsorption

243

of As would be minimized under alkaline condition) (Figure 1C). Plot of [p-ASA] vs

244

[ferrate]reacted showed a linear relationship, and the calculated slope is - 0.44 ± 0.04. This

245

reveals that the stoichiometric ratio of ferrate with p-ASA is around 2:1, and reaction

246

follows the stoichiometry:

247

9 Fe(VI) + 4 p-ASA → 9 Fe(III) + products

248

Previous studies showed that inorganic As species would be released in the oxidation

249

of p-ASA. By analyzing the samples with mass spectrometry (ICP-MS and

250

HPLC/ESI-QTOF-MS) and comparing mass spectrum information with chemical

251

standards, it was found that As(V) is the dominant component of inorganic As species,

252

while p-AP and nitarsone are the main organic oxidation products. Besides, NO3- was

253

also formed in the ferrate oxidation of p-ASA (Figure S3) (detailed information about the 13



254

identification of oxidation products is shown in Text S7; proposed reaction pathway is

255

shown in “reaction mechanism” section). Formation profile of As(V), NO3-, p-AP, and

256

nitarsone in the ferrate oxidation of p-ASA at different molar ratios was examined

257

(Figure 1D). When low level of ferrate (ferrate/p-ASA < 1) was applied, less than 30% of

258

p-ASA was oxidized into As(V) and p-AP. As(V) is stable and can be removed by ferrate

259

resultant ferric (oxyhydr) oxides 33. p-AP could be further oxidized when higher level of

260

ferrate was applied

261

p-ASA could be oxidized with the formation of As(V) species and trace amount of

262

nitarsone and NO3-. When ferrate/p-ASA molar ratio surpassed 3.3, 80% of p-ASA was

263

oxidized into As(V) and 20% of p-ASA was oxidized into nitarsone based on As mass

264

balance. No abatement of nitarsone was observed when high level of ferrate was applied.

265

When 5 μM of nitarsone reacted with 50 μM of ferrate, no oxidation of nitarsone was

266

observed either (Figure 1E). These results suggested that nitarsone was resistant to ferrate

267

oxidation, while over 85% of nitarsone was adsorbed by ferrate resultant particles and

268

removed in filtration process (Figure 1E). Besides, the content of NO3- also increased

269

when high level of ferrate was used. This indicates that some N-containing compounds

270

were further oxidized by ferrate with the cleavage of C-N bond and formation of NO3- in

271

the system.

272

3.2 Removal of total-As and TOC

34, 36.

When ferrate/p-ASA molar ratio increased to 2.3 ~ 2.5, all of

14


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273

Carcinogenic As species could be released in the transformation of organoarsenicals

274

2, 37,

275

organoarsenicals pollution. Variation of p-ASA, As(III), As(V), and the total As content

276

as a function of reaction time was examined (ferrate/p-ASA = 10:1, pH = 7.0) (Figure

277

2A). Concentration of p-ASA decreased rapidly with the increase of As(V) content. One

278

minute later, p-ASA concentration was 0.13 μM, and As(V) concentration was 4.07 μM.

279

Concentration of As(III) was below 0.02 μM during the reaction process. This data is in

280

accordance with above result (Figure 1D and S15), that over 80% of p-ASA was

281

transformed into As(V) and around 20% of p-ASA was transformed into nitarsone.

and controlling the released inorganic As is a critical issue for the remediation of

282

Removal of total-As in the ferrate oxidation of p-ASA was studied (Figure 2B).

283

When 5 μM of p-ASA reacted with 50 μM, 75 μM and 100 μM of ferrate, total-As

284

content decreased to 0.56 μM, 0.23 μM and 0.09 μM respectively in filtered solution

285

samples after 10 min of reaction. This suggests that ferrate could effective control

286

total-As content in the reaction with p-ASA.

287

Chemical state of As in p-ASA and ferrate resultant particles was analyzed by XPS

288

(Figure S4). As 3d fitting peak binding energy (BE) of p-ASA was 44.4 eV and can be

289

assigned to As(III) (44.3 ~ 44.5 eV). As 3d fitting peak BE of ferric particles was 45.3 eV

290

and can be assigned to As(V) (45.2 ~ 45.6 eV)

291

oxidation of p-ASA, the -AsO(OH)2 moiety was oxidized to As(V). Prucek et al

292

investigated the ferrate oxidation of As(III) and found that the oxidation products [As(V)]

38.

This indicates that in the ferrate

15



Page 16 of 42

293

could be removed by ferric (oxyhydr) oxides through crystal structure incorporation

294

Besides the peak centered at 45.2 eV of As-bearing samples, they observed another small

295

peak closing to 48 eV. Together with Mössbauer data, they concluded that this

296

phenomenon represents that As species incorporated into the crystal structure of ferric

297

(oxyhydr) oxides. We also studied the reaction of ferrate with inorganic As(III), and

298

observed two XPS peaks (one main peak is at 45.2 eV, and a small peak is at 47.8 eV)

299

exist in the ferric solids (Figure S4D). In comparison, only one XPS peak at 45.2 eV

300

exists in the ferric solids formed in the ferrate oxidation of p-ASA (Figure S4B). This

301

indicates that the As(V) species formed in the ferrate oxidation of p-ASA was mainly

302

removed by ferric (oxyhydr) oxides through surface adsorption.

39.

303 304

Figure 2. Variation of total As, p-ASA, As(III), and As(V) content in the reaction of p-ASA (5 μM) 16


Page 17 of 42


305

with ferrate (50 μM) [1 mM of hydroxylamine hydrochloride and 0.5% (v.t.) of HCl were added to

306

dissolve the ferric particles] (A). Variation of total As content when different dosages of ferrate

307

reacted with p-ASA (5 μM) (solution samples were filtered with 0.22 μm glass fiber membrane) (B).

308

FTIR result about the ferric particles formed in the self-decomposition of ferrate and in the ferrate

309

oxidation of p-ASA. Green areas indicate peaks with similar vibration, while gray areas indicate peaks

310

with different vibration (C). Removal ratio of TOC of p-ASA treated by different molar ratios of

311

ferrate, HClO, permanganate [Mn(VII)], and ozone within 2 hours. Fe(VI) (acidified) indicates that

312

the solution samples (ferric solids) were dissolved with HCl, which represents the eliminated TOC in

313

ferrate oxidation process. Fe(VI) (filtered) indicates that the solution samples were filtered through

314

0.22 μm glass fiber filter to remove ferric particles (D). Experimental conditions: T = 25 °C, pH = 7.0.

315

As(V) species could be removed by ferrate resultant particles, and FTIR analysis is

316

used to study the chemical properties of ferric particles formed in the self-decomposition

317

of ferrate and in the reaction of p-ASA with ferrate (Figure 2C). Both samples have

318

intense peaks at 3400 and 1640 cm-1, which can be assigned to the stretch of OH groups

319

of H2O 40. The peaks at 1120 cm-1 could be assigned to OH stretch of α-FeOOH 41, while

320

the peaks near at 680, 610, and 480 cm-1 corresponded to the vibration of Fe–O bonds

321

42-44.

322

836 cm-1, that can be ascribed to the symmetric stretching vibration of As-(OFe) 21, 45.

323 324

In comparison, the sample formed in ferrate/p-ASA group has a vibrational peak at

The peaks at 1527, 1420, 1358 cm-1 can be attributed to vibrations correlating with -COO- symmetric stretching, CH2 wagging, and C-O stretching, respectively 17


45-47.


Page 18 of 42

325

Besides FTIR, XPS analysis also showed that four peaks corresponding to C-C/C=C/C-H

326

(284.8 eV), C-C(OH)=O (285.7 eV), C-O (286.8 eV) and O=C-O (289.2 eV)

327

enveloped in the C1s peak of the ferric solids resulted in the ferrate oxidation of p-ASA

328

(Figure S4C). These organics may be the oxidation products formed in the ferrate

329

oxidation of p-ASA, and were adsorbed or complexed onto the surface of ferrate resultant

330

ferric (oxyhydr) oxides.

48

were

331

TOC removal efficiency is a critical standard for evaluating the quality of treated

332

water and effectiveness of water treatment procedure. Compared with ferrate oxidation

333

and ozonation, HClO oxidation and Mn(VII) oxidation are less effective for the removal

334

of TOC in the system. For chlorination of organics, chlorine atoms would be added onto

335

the structure of target compound through substitution reaction, and HClO was always

336

used as disinfectant agent. Mn(VII) could react with p-ASA but the reactivity is not high

337

(Figure 1B). These factors made the TOC removal efficiencies in HClO and Mn(VII)

338

groups lower than 5%. Ozone is a strong oxidant and could react with p-ASA. Ozonation

339

removed around 18.4%, 29.2%, and 37.6% of TOC in the three groups, respectively.

340

Compared with chlorination, Mn(VII) oxidation, and ferrate oxidation, ozonation is the

341

most effective method for the oxidation of p-ASA.

342

Interestingly, for the p-ASA treated by different level of ferrate, the TOC removal

343

ratio was largely improved in filtered samples than those in acidified samples (Figure

344

2D). When the initial molar ratio of ferrate/p-ASA is 20:1, TOC removal efficiency is 18


Page 19 of 42


345

18.1% in ferrate (acidified) group and 58.3% in ferrate (filtered) group. Compared with

346

ferrate oxidation, ferrate resultant particles removed around 40% of TOC in the system.

347

In above section we showed that nitarsone is a resistant oxidation product and could be

348

adsorbed by ferrate resultant ferric (oxyhydr) oxides (Figure 1E). Considering that 20%

349

of p-ASA was oxidized into nitarsone (Figure 1D) and around 85% of nitarsone was

350

adsorbed (Figure 1E), the amount of nitarsone removed in ferrate (filtered) group equals

351

to 17% of TOC. This indicates that ferrate resultant particles removed around 23% of

352

organics (oxidation products of p-ASA, besides nitarsone) in the system. This TOC

353

removal efficiency is much higher than the organics eliminated in ferrate oxidation

354

process.

355

Literally, chemical oxidation of organic pollutants refers to the transformation of

356

structure of target pollutants through oxygen transfer process, and elimination of function

357

groups of target pollutants with non-oxidative mechanism such as β-elimination 49. These

358

processes may degrade organic pollutant into lower molecular weight products. In

359

comparison, mineralizing dissolved organics through chemical oxidation is difficult and

360

energy consuming. Ozone is a strong oxidant and ozonation of p-ASA removed 37.6% of

361

TOC in 20:1 group, 2 to 25 times higher than the TOC removal in chlorination,

362

permanganate oxidation and ferrate oxidation processes. However, ferrate resultant

363

particles removed 40% of TOC in 20:1 group (Figure 1D), much higher than those

364

eliminated by ferrate oxidation and even higher than those eliminated by ozonation. 19



365

Besides ferrate oxidation, ferrate resultant particles have great potential for the removal

366

of organics.

367

Considering that the ferrate resultant ferric (oxyhydr) oxides are composed by Fe2O3,

368

FeOOH and amorphous ferric, effects of Fe2O3, FeCl3 and ferrate resultant particles on

369

nitarsone adsorption were compared (Figure S5). Ferrate resultant particles showed

370

highest nitarsone adsorption ratio (> 85%) and shortest reaction time (< 1 min) than that

371

of Fe2O3 and FeCl3. These ferric (oxyhydr) oxides are small in size (nano size), highly

372

dispersed in water (in situ formed in the reduction of ferrate), and have large specific

373

surface area. These factors could enhance the interaction opportunity of ferric (oxyhydr)

374

oxides with target pollutants and facilitate their removal.

375 376

Figure 3. TEM photos of particles formed in ferrate oxidation of p-ASA (in situ), mixture of ferrate 20


Page 20 of 42

Page 21 of 42


377

resultant particles (self-decay for an hour) with p-ASA (ex situ), and ferrate resultant particles

378

(self-decomposition for an hour) (blank). Experimental conditions: [p-ASA]0 = 5.0 μM, [ferrate]0 =

379

50.0 μM, T = 25 °C, pH = 7.0.

380

TEM was used to analyze the physical properties of ferrate resultant particles (Figure

381

3). The average size of particles in situ formed in the ferrate oxidation of p-ASA is 4.37

382

nm. In comparison, the average size of particles formed in the reduction of ferrate

383

without p-ASA is 6.45 nm. Particles formed in the reaction of ferrate with p-ASA is

384

smaller than the particles in “blank” and “ex situ” groups. As mentioned in above section,

385

inorganic As(V) species and organics (such as nitarsone) could be adsorbed by ferric

386

(oxyhydr) oxides. These foreign components may inhibit the growth of ferric

387

nanoparticles 39.

388

Besides particle size, TEM photos showed that compared with the particles formed in

389

blank group, the “in situ” and “ex situ” formed particles are surrounded/coated with

390

semi-transparent amorphous substance (Figure 3 and Figure S16). This substance may be

391

the

392

microscopy/energy-dispersive

393

confirmed that the ferric (oxyhydr) oxides particles are mixed with C and As elements

394

(Figure S6). Combining with above analysis, As species and organics formed in the

395

ferrate oxidation of p-ASA may be adsorbed by ferrate resultant nanoparticles or be

396

complexed on their surface, which inhibit the growth of these ferric nanoparticles.

organics

adsorbed

by

ferric

X-ray

(oxyhydr)

spectrometry

oxides.

Scanning

(SEM-EDX)

21


electron

analysis

further


397

3.3 Reaction mechanism

398

In above sections we showed that As(V), p-AP, and nitarsone are formed in the

399

ferrate oxidation of p-ASA when the initial ferrate/p-ASA ratio is below 3:1. As(V) and

400

nitarsone are resistant to ferrate oxidation, while p-AP can be further oxidized 34, 36. In the

401

reaction process, solution color was shifted from transparent to pale pink in an hour

402

(Figure S7). We speculate that azo compounds may form in the ferrate oxidation of p-AP

403

18.

404

(4,4'-(diazene-1,2-diyl) diphenol and 4,4'-(hydrazine-1,2-diyl) diphenol) showed similar

405

ionization patterns with that of p-AP from m/z 40 to 90 Da (Figure S8). These

406

compounds contain similar chemical moieties or functional groups with p-AP, and may

407

be the oxidation product of p-AP. Besides 4,4'-(diazene-1,2-diyl) diphenol and

408

4,4'-(hydrazine-1,2-diyl) diphenol, another compound (m/z = 138.02 Da) was identified

409

under ESI- mode. After comparing with chemical standard, we confirmed that this

410

compound is p-nitrophenol (MW = 139.02 Da), and it can be oxidized by ferrate with the

411

formation of benzoquinone and NO3- (Figure S9 and S3).

By analyzing the oxidation products under ESI+ mode, 2 identified compounds

412

Combining the identified products, reaction stoichiometry, and concentration

413

variation of relevant products, reaction pathway of p-ASA with ferrate is illustrated in

414

Figure 4. Ferrate initially attacks the As-C bond of p-ASA through oxygen transfer

415

process, with the formation of p-AP and As(V). When high level of ferrate

416

(ferrate/p-ASA > 3.5) was applied, around 80% of p-ASA would be oxidized into As(V) 22


Page 22 of 42

Page 23 of 42


417

and p-AP, while the residual p-ASA would be transformed into nitarsone. Compared with

418

As(V) and nitarsone, p-AP is easily oxidized. Aminophenol radicals would form in the

419

ferrate oxidation of p-AP through one-electron transfer process. These radicals can

420

further react with ferrate, with the formation of p-nitrophenol, benzoquinone, NO3-, and

421

other oxidation products. On the other hand, some aminophenol radicals would combine

422

via radical−radical self-coupling process, with the formation of 4,4'-(hydrazine-1,2-diyl)

423

diphenol and 4,4'-(diazene-1,2-diyl) diphenol in the system. 4,4'-(diazene-1,2-diyl)

424

diphenol may be further oxidized by ferrate. Based on N-mass balance, around 17% of

425

p-ASA was oxidized by ferrate with the formation of NO3- as the end product

426

(ferrate/p-ASA = 10:1, pH 7.0).

427 428 429

Figure 4. Proposed reaction pathway of p-ASA with ferrate.

Over 98% of As(V) species formed in the reaction process would be adsorbed by 23



430

ferrate resultant ferric (oxyhydr) oxides through surface adsorption process. Firstly,

431

hydroxy groups of ferric (oxyhydr) oxides would interact with As(V) species through

432

hydrogen bond and lead to the adsorption of As(V) onto the particle surface. Secondly,

433

As(V) species is negatively charged, while the zeta potential of ferrate resultant ferric

434

(oxyhydr) oxides is around 0 mV at pH 7.0 (Figure S10). Electrostatic attraction among

435

As(V) species and ferric (oxyhydr) oxides could enhance to the adsorption of As(V).

436

Thirdly, As(V) species could complex with ferric (oxyhydr) oxides through the formation

437

of As-(OFe) bond (Figure 2C). Compared with ferrate oxidation of inorganic As(V), no

438

incorporation of As(V) species into the crystal structure of ferric (oxyhydr) oxides was

439

observed (Figure S4).

440

Nitarsone would form in the ferrate oxidation of p-ASA, and over 85% of nitarsone

441

was removed when the initial ferrate/nitarsone molar ratio is 10:1 (Figure 1E). Based on

442

As-mass balance, over 90% of total As was removed in the forms of As(V) and nitarsone

443

by the ferric nanoparticles (ferrate/p-ASA = 10:1, pH 7.0). When high level of ferrate

444

was applied (i.e. ferrate/p-ASA = 20:1), total-As removal efficiency could surpass 99%

445

(Figure 2B).

446

In above sections we showed that adsorption is also a main pathway for the removal

447

of organics in the system. The results of TOC (Figure 2), TEM (Figure 3), and

448

SEM-EDX (Figure S6) analysis suggested that ferric particles adsorbed organics. The

449

result of FTIR and XPS (Figure S4) analysis revealed that -COO- bond may form in the 24


Page 24 of 42

Page 25 of 42


450

complexation of organics with ferric particles. Besides complexation, hydrogen bond

451

between negatively charged ferric (oxyhydr) oxides and hydroxy groups of organics may

452

also facilitate the adsorption of organics.

453

3.4 Influence of background constituents on the oxidation of p-ASA and removal of

454

As

455

Background constituents such as dissolved organic matter (DOM) and electrolytes

456

ubiquitously exist in natural waters and would influence the chemical oxidation of

457

pollutants 50. The effects of SRHA, Ca2+, Cl-, and PO43- on the ferrate oxidation of p-ASA

458

were investigated. When the content of SRHA increased from 0 mg/L to 1 mg/L, 3 mg/L,

459

and 5 mg/L, the residual ratio of p-ASA increased from 0% to 6%, 16%, and 30% in 10

460

min of reaction, respectively (Figure 5A). SRHA negatively influenced the ferrate

461

oxidation of p-ASA, and the depression effect increased with the elevation of SRHA

462

content.

463

Previous investigations explored the effects of HA on the control of environmental

464

pollutants with ferrate, and many of them found that HA would decrease the removal

465

ratio of target pollutants by ferrate. Wenk et al. investigated the influence of DOM on the

466

oxidation of organic compounds, and speculated that the oxidation intermediate may be

467

reduced back to the parent form by the co-existing DOM 51. This process would result in

468

the decrease of removal of target pollutants. On the other hand, SRHA may competitively

469

react with ferrate and affect ferrate exposure concentration in the system, which in turn 25



470

Page 26 of 42

negatively influence the ferrate oxidation of p-ASA.

471 472

Figure 5. Influence of SRHA (A) and electrolytes (B) on the ferrate oxidation of p-ASA; effects of

473

cationic species (Ca2+, Mg2+), anionic species (SiO32-, PO43-), SRHA, and solution pH on the removal

474

of total-As (C), and zeta potential of ferrate resultant particles (D). Experimental conditions: [p-ASA]0

475

= 5 μM, [ferrate]0 = 50 μM, T = 25 ℃, reaction time: 60 min.

476

For the co-existing electrolytes, Ca2+ and Cl- (10 mM) showed no obvious effects,

477

while PO43- (10 mM) negatively influenced the oxidation process (Figure 5B). After 3

478

min of reaction, the content of p-ASA was below HPLC detection limit in control, Cl-

479

and Ca2+ groups, while 93% of p-ASA was oxidized in PO43- group. Previous studies

480

showed that phosphate would inhibit the ferrate oxidation of Br- and HOI

481

speculate that PO43- species may complex with ferrate and affect ferrate exposure

482

concentration, but the difference of ferrate content in relevant groups was below 4 μM 26


52, 53.

We

Page 27 of 42


483

(Figure S11). The effect of PO43- on ferrate exposure concentration was not obvious.

484

Considering that intermediate iron species [Fe(IV) and Fe(V)] may form in ferrate

485

oxidation process, PO43- may influence the oxidation ability of intermediate iron species

486

and thus impact the oxidation of p-ASA. The underlying mechanism warrants further

487

investigation.

488

Background constituents would affect the removal of hazardous ion with ferrate

489

resultant particles, and lead to the desorption of captured ion 54. When 10 mM of Ca2+,

490

Mg2+, and HCO3- exist in the solution (pH = 7.0), the removal of total-As was not greatly

491

influenced (Figure 5C). Acidic condition (pH 6.0) is in favor for the removal of As (>

492

99%), while the As removal ratio decreased under alkaline condition (pH 8.0, ~ 34%).

493

The point of zero charge (pHpzc) of ferrate resultant nanoparticles was 6.8 (Figure S10).

494

These ferric particles were positively charged under acidic conditions and negatively

495

charged under alkaline conditions. Electrostatic force makes the As(V) (AsO43-) easily

496

captured by ferric particles under acidic condition and hard to be captured under alkaline

497

condition.

498

Total-As removal ratios decreased with the existing of SRHA, PO43- and SiO32-.

499

When the content of SRHA, PO43- and SiO32- increased from 0 to 0.5 mgC/L, 0.1 mM and

500

1 mM, respectively, removal ratios of As decreased from 90% to 15%, 10%, and 12%,

501

respectively. In above section we speculated that there are 3 kinds of functions

502

participating in the removal of As species with ferric (oxyhydr) oxides: hydrogen bond, 27



503

electrostatic attraction, and surface complexation. When SiO32-, PO43-, SRHA and OH-

504

exist in the solution, they would coat on the surface of ferric (oxyhydr) oxides 55 or form

505

inner-sphere complexes 56, decreasing the zeta potential of ferric (oxyhydr) oxides. As(V)

506

species is negatively charged under neutral pH condition. The electrostatic repulsion

507

among negatively charged ferric (oxyhydr) oxides and As(V) species would decrease the

508

removal ratio of As(V), and hinder the aggregation of ferric nanoparticles into floc. In

509

comparison, ferric (oxyhydr) oxides is positively charged under acidic condition (pH

510

6.0), and As(V) mainly exists as HAsO42- specie at pH 6.0. The removal efficiency of

511

As(V) is higher in pH 6.0 group than those in other groups, which also suggests that

512

electrostatic attraction plays an important role for the removal of As(V) with ferric

513

(oxyhydr) oxides.

514

3.5 Toxicity assay

515

p-ASA would be oxidized by ferrate and the total-As can be simultaneously

516

removed, while the toxicity of soluble oxidation products is unknown. The effects of

517

p-ASA, As(V), As(III), and ferrate treated p-ASA solution on the growth of E. coli K12

518

and on the luminescent intensity of P. phosphoreum were investigated (Figure 6). For the

519

E. coli K12 cultured in control group, the OD600 value increased to 2.3 within 24 h, and

520

maintained around 2.5 in the following 24 h (Figure 6A). In comparison, when 2.5 mM

521

of inorganic As(V) and As(III) exist in the medium, the solution OD600 values were

522

around 0.6 in both groups. The inorganic As(V) and As(III) species severely inhibited the 28


Page 28 of 42

Page 29 of 42

523


growth of E. coli K12.

524 525

Figure 6. Growth curve of E. coli K12 in control group (LB medium), p-ASA (2.5 mM), As(V) (2.5

526

mM), As(III) (2.5 mM), and ferrate treated p-ASA solution (2.5 mM of p-ASA reacted with 25 mM of

527

ferrate for an hour, filtered) (A), and evaluation of acute toxicity of ferrate (1 mM, self-decay for 24

528

h), p-ASA (0.1 mM), p-AP (0.1 mM), nitarsone (0.1 mM), As(III) (0.1 mM), As(V) (0.1 mM), and

529

oxidation products of p-ASA and p-AP ([p-ASA]0 = 0.1 mM, [p-AP]0 = 0.1 mM, reacted with 1 mM

530

of ferrate for 2 h, filtered) with P. phosphoreum (B).

531

For the microbes in p-ASA group, the OD600 peak value approached 1.7 after 34 h

532

of culture, 0.67 lower than those in control group. This suggests that p-ASA (2.5 mM)

533

would inhibit the growth of E. coli K12, while the antibiotic effect is less severe than that 29



534

of As(V) and As(III). For the E. coli K12 cultured in ferrate treated p-ASA solution, the

535

OD600 peak value increased to 2.7 after 48 h of culture, 0.2 higher than that in control

536

group, and much higher than those in p-ASA, As(III) and As(V) groups. In above

537

sections we showed that 1), ferrate oxidation could degrade p-ASA into As(V),

538

p-aminophenol (p-AP), nitarsone, NO3-, and other products; 2), over 90% of total As

539

could be removed by ferrate resultant particles (ferrate/p-ASA = 10:1, Figure 2B); 3),

540

around 37% of organics could be removed by ferrate resultant particles (ferrate/p-ASA =

541

10:1, Figure 2D). These processes largely eliminated the antibiotic effect of p-ASA and

542

residual products on the growth of E. coli K12.

543

The inhibition effect of relevant samples on the luminescent intensity of P.

544

phosphoreum is used to reflect the acute toxicity (Figure 6B). Decomposition products of

545

ferrate (ferric particles) showed no influence on the luminescent intensity of P.

546

phosphoreum, while over 40% of luminescent intensity was inhibited by As(III), As(V),

547

and nitarsone. In comparison, luminescent intensity inhibition ratios in p-ASA and p-AP

548

groups were around 10% and 18%, respectively. These results are in accordance with

549

previous data, in which the inorganic As species [As(V) and As(III)] are highly toxic, and

550

toxicity of p-ASA is not severe. Toxicity of nitarsone is more severe than that of p-ASA,

551

suggesting that toxic compounds may form in the transformation of organic pollutants.

552

Compared with p-ASA, the ferrate oxidation products formed in ferrate/p-ASA = 5:1

553

group were more toxic. This may because some oxidation products (such as nitarsone, 30


Page 30 of 42

Page 31 of 42


554

As(V) and p-nitrophenol) formed in the reaction process were not fully oxidized or

555

removed by ferrate resultant particles. When higher levels of ferrate were applied

556

(ferrate/p-ASA = 10:1 and 20:1), luminescent intensity inhibition ratios were negative.

557

This suggests that the activity and metabolization of P. phosphoreum was not depressed.

558

In above sections we showed that p-ASA would be oxidized by ferrate with the formation

559

of As(V), p-AP, nitarsone, and NO3-. The As(V), nitarsone and some part of organics can

560

be removed through adsorption process by the ferrate resultant particles, and p-AP can be

561

further oxidized into p-nitrophenol, 4,4'-(diazene-1,2-diyl) diphenol, NO3- and other

562

products. When 0.1 mM of p-AP was oxidized by 1 mM of ferrate for an hour, the

563

resultant solution also showed no toxicity to P. phosphoreum. This indicates that ferrate

564

treatment (including oxidation and adsorption) is effective for eliminating the toxicity of

565

p-ASA.

566

4. Environmental implications

567

Physical adsorption has many advantages for eliminating pollutants from water. It

568

does not introduce additional chemicals (under ideal condition), and no hazardous

569

transformation products would be formed. However, emerging organic pollutants always

570

exist at low concentration level. Large amount of adsorbent is required to achieve

571

satisfactory removal efficiency. Nanomaterials have been designed for the removal of

572

pollutants, yet they are case-specific, expensive, and would be influenced by background

573

water matrix. 31



574

Chemical oxidants could effectively degrade organic pollutants, but toxic

575

transformation by-products may be formed in the reaction process. The easily assimilable

576

organic carbon formed in the transformation of organics would negatively influence the

577

microbiological stability of treated water

578

release organics into water. Some transformation products and microbe metabolites may

579

even become disinfection by-products precursors in following water treatment procedures

580

57.

581

microbiological stability of treated water, yet mineralization of organic pollutants with

582

chemical oxidation was energy consuming. Even advanced oxidation processes could

583

mineralize small part of dissolved organics in polluted water.

25,

and reproduced microbes would in turn

Ultimately removing organic components could improve the chemical and

584

Ferrate draws extensive attention as a promising multi-purpose water treatment agent

585

for oxidation, adsorption, coagulation, and disinfection 58. Studies showed that ferrate is

586

effective for the oxidation of organics and controlling inorganic species, while the effect

587

of ferrate resultant nanoparticles on the adsorption of organics received little attention.

588

Oxygen transfer is a main reaction pathway happening in ferrate oxidation process, and

589

the hydroxylation products formed in reaction process have high affinity with ferric

590

(oxyhydr) oxides. Meanwhile, ferric (oxyhydr) oxides newly formed in the reduction of

591

ferrate is well dispersed and small in size. These properties make ferrate resultant

592

nanoparticles a promising agent for the subsequent removal of organic compounds after

593

ferrate oxidation. Investigating the effectiveness and mechanism of ferrate resultant 32


Page 32 of 42

Page 33 of 42


594

nanoparticles on removal of organic pollutants, and developing relevant methods to

595

enhance this process could provide a new perspective for pollutants control.

596 597

Acknowledgments

598

The authors sincerely appreciate the thoughtful comments and constructive

599

suggestions from the anonymous reviewers and editor. This work was financially

600

supported by the National Key R&D Program of China (2017YFA0207203), and the

601

National Natural Science Foundation of China (Grant No. 51808163).

602 603

Supporting Information

604 605

Seven text, one table, sixteen figures about the experimental operation procedures and additional experimental data are presented in supporting information.

606 607

References

608

1.

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2.

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Arsenite from Roxarsone Bioreduction by Exoelectrogenic Bacteria. Environmental Science &

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Technology Letters 2017, 4, (8), 350-355.

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solubility and distribution in poultry waste and long-term amended soil. Science of The Total

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tissues from live poultry markets of Guangdong province, China. Environmental Science &

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Technology 2017, 51, (6), 3508-3517.

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Anaerobic biotransformation of roxarsone and related N-substituted phenylarsonic acids.

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Environmental science & technology 2006, 40, (9), 2951-2957.

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M.; Zhou, D., Fate of As(III) and As(V) during Microbial Reduction of Arsenic-Bearing Ferrihydrite

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Facilitated by Activated Carbon. ACS Earth and Space Chemistry 2018, 2, (9), 878-887.

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Removal of Organoarsenic with Ferrate and Ferrate Resultant

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