Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2

Subscriber access provided by University of Winnipeg Library

Remediation and Control Technologies

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-like Reaction and Organic Pollutant Degradation Chu Dai, Xike Tian, Yulun Nie, Hong-Ming Lin, Chao Yang, Bo Han, and Yanxin Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b01448 • Publication Date (Web): 04 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018

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

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

Page 1 of 26

Environmental Science & Technology

1

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in

2

Fenton-like Reaction and Organic Pollutant Degradation

3

Chu Dai†, Xike Tian*, †, Yulun Nie†, Hong-Ming Lin‡, Chao Yang†, Bo Han†, Yanxin

4

Wang§ †

5

Faculty of Material Science and Chemistry, China University of Geosciences,

6

Wuhan, 430074, P.R. China. ‡

7 8 9

§

Department Materials Engineering, Tatung University, 104 Taipei, Taiwan.

School of Environmental Studies, China University of Geosciences, Wuhan, 430074, P. R. China.

10 11

ABSTRACT: The development of efficient heterogeneous Fenton catalysts is mainly

12

by “Trial-and-Error” concept and the factor determining H2O2 activation remains

13

elusive. In this work, we demonstrate that suitable facet exposure to elongate O-O

14

bond in H2O2 is the key parameter determining the Fenton catalyst’s activity. CuFeO2

15

nanocubes and nanoplates with different surface facets of {110} and {012} are used to

16

compare the effect of exposed facets on Fenton activity. The results indicate that

17

ofloxacin (OFX) degradation rate by CuFeO2 {012} is four times faster than that of

18

CuFeO2 {110} (0.0408 vs. 0.0101 min-1). In CuFeO2 {012}-H2O2 system, OFX is

19

completely removed at a pH range 3.2-10.1. The experimental results and theoretical

20

simulations show that •OH is preferentially formed from the reduction of absorbed

21

H2O2 by electron from CuFeO2 {012} due to suitable elongation of O-O (1.472 Å)

22

bond length in H2O2. By contrast, the O-O bond length is elongated from 1.468 Å to

1 ACS Paragon Plus Environment


23

3.290 Å by CuFeO2 {110} facet, H2O2 tends to be dissociated into -OH group and

24

passivates {110} facet. Besides, the new formed ≡Fe2+* on CuFeO2 {012} facet can

25

accelerate the redox cycle of Cu and Fe species, leading to excellent long-term

26

stability of CuFeO2 nanoplates.

27

 INTRODUCTION

28

The manipulation over the electron states of various oxidants (O2, H2O2 and O3 etc.)

29

holds the key to modulate their conversion into radicals in a wide variety of oxidation

30

reactions.1-5 For example, activation of H2O2 on the surface of catalysts, so called the

31

heterogeneous Fenton-like reaction, plays a central role in the efficient abatement of

32

organic pollutants in water.6-8 Generally, the interaction of organic compounds and

33

H2O2 is essentially limited due to the low redox potential of H2O2 (1.77 eV).9,10 As

34

well-known, the efficient degradation and even mineralization of these pollutants can

35

be obtained by •OH radical with high redox potential (2.8 eV) generated from the

36

reduction of H2O2 with different Fenton-like catalysts, such as Fe3O4, Fe2O3, FeOOH

37

and FeOOH@GO etc.11-16 However, H2O2 can react with catalyst surface via redox

38

reactions for •OH radical or catalytic decomposition into O2.17,18 For the reason above,

39

it is urgent to provide a heterogeneous Fenton catalyst to inhibit O2 formation but

40

favor the H2O2 conversion into •OH.

41

Based on the previous reports, the conversion of H2O2 to •OH over Fenton catalyst is

42

a spontaneous process depending on the reactive sites rather than total surface area,

43

the oxidation state of active metals and solid-surface-area to solution-volume-ratio

44

(SA/V).19 However, most of catalysts are characterized by extensive randomness in


Page 2 of 26

Page 3 of 26


45

terms of surface structure and defects.20-22 Hence, in depth understanding of the

46

surface Fenton reaction process needs to be explored. The issues include hydrogen

47

bonding between H2O2 and the hydroxylated surfaces of catalysts; the degree of

48

interaction between the O atoms of H2O2 and the surface exposed metal cations within

49

catalysts; and the exact reactive sites for efficient H2O2 decomposition. All these

50

concerns will determine the reaction mechanism that H2O2 decomposition into •OH or

51

O2.23,24

52

In fact, the surface H2O2 activation and efficient electron transfer from active metal to

53

absorbed H2O2 are the key steps that determine the performance of heterogeneous

54

Fenton catalyst. Hence, the crystal surface of nanoparticle is of paramount importance

55

for the catalyst’s reactivity. The surface facets on the crystals have a huge impact on

56

the molecular adsorption process due to the different crystal energies in the different

57

atomic arrangements. Hence, it is possible to tailor the surface properties of Fenton

58

catalyst by manipulating the surface density of atomic steps, ledges, and kinks.25 Via

59

the Arrhenius and the transition state theory (TS), the activation energies and

60

enthalpies of Fenton reactions help to understand the metal-molecule interactions,23

61

however, it is still difficult to describe the chemistry at the atomic scale. Therefore,

62

the design and synthesis of singlet-facet nanocrystals is a big challenge to explore the

63

complex surface chemistry.

64

Herein, the nanocube CuFeO2 {110} and nanoplate CuFeO2 {012} are synthesized to

65

study the effect of facet exposure on Fenton reaction performance. Their Fenton-like

66

activity was evaluated by the OFX degradation rate and degradation efficiency. It



67

show that OFX can be more efficiently degraded on {012} facets with a reaction rate

68

constant of 0.0408 min-1 vs. 0.0101 min-1 on {110} facets. The theoretical simulations

69

and characterizations were conducted to clarify the difference of {012} and {110}

70

facets in H2O2 activation into reactive oxygen species (ROS). Moreover, the effect of

71

initial solution pH and long-term stability of CuFeO2 {012} were further explored.

72

The intrinsic electron transfer between Cu and Fe element, especially the new formed

73

Fe2+* species for the excellent Fenton activity and stability of CuFeO2 {012} was also

74

discussed. Therefore, this study demonstrates the facet control is a critical parameter

75

to design a heterogeneous Fenton catalyst in water treatment.

76

 EXPERIMENTAL SECTION

77

Nanocrystal Synthesis. CuFeO2 nanoplates with exposed {012} facets (denoted as

78

CuFe-012) is prepared according to the following procedure. 0.1 M Cu(NO3)2·3H2O

79

and Fe(NO3)3·9H2O solution is added dropwise to the 0.8 M NaOH solution under

80

constant stirring for full precipitation. After washing to a neutral pH, the precipitation

81

is re-dispersed into 50 mL distilled water and 5 mL ethylene glycol is then added as

82

reducing agent. The well mixed dispersion is transferred into Teflon-lined autoclave

83

and heated in an oven at 200 °C for 12 h. The obtained black precipitates are collected

84

and repeatedly washed with distilled water and absolute ethyl alcohol. Finally, the

85

samples are vacuum-dried at 60°C overnight. CuFeO2 nanocubes with exposed {110}

86

facets (CuFe-110) are synthesized under the similar conditions. The precipitation is

87

transferred into Teflon-lined autoclave directly without washing step. For comparison,

88

Fe2O3 and Cu2O are prepared individually using Fe(NO3)3 and Cu(NO3)2 as precursor,


Page 4 of 26

Page 5 of 26


89

respectively, following the same procedure of CuFe-110.

90

Characterization. Powder X-ray diffraction (XRD) with monochromatic Cu Kα

91

(λ=1.5406 Å) is recorded by a Bruker AXS D8-Focus diffractometer. The surface

92

morphology is studied using field emission scanning electron microscopy (FESEM,

93

Hitachi SU-8010) equipped with an attached Oxford Link ISIS energy-dispersive

94

X-ray spectroscopy (EDS) and transmission electron microscopy (TEM, Philips CM

95

12). X-ray photoelectron spectroscopy (XPS) is examined by the MULTILAB2000

96

electron spectrometer with 300W Al Kα radiation. The Brunauer-Emmett-Teller (BET)

97

surface area of the prepared sample is tested using Micromeritics ASAP 2020 HD88

98

adsorption analyzer. Electron spin resonance (ESR) spectra are obtained using a

99

FA200 ESR spectrometer equipped with a quanta-Ray Nd: YAG laser system as the

100

irradiation light source (λ=532 nm). The settings of center field, microwave frequency,

101

and power are 3480.00 G, 9.79 GHz, and 5.05 mW, respectively. The leaching of iron

102

is determined by ICP-MS (iCAP Qc, Thermo Scientific).

103

Computational Methods. The chemisorption and reaction of H2O2 on CuFeO2

104

surface are investigated by spin-polarized density functional theory (DFT) using the

105

Vienna ab-initio simulation package (VASP). The projector augmented wave (PAW)

106

method is used to describe electron-ion interaction with Perdew-Burke-Ernzerh (PBE)

107

of functional for exchange-correlation energy. An energy cutoff of 400 eV is used for

108

the plane-wave expansion of the electronic wave function. The optimized crystal

109

structure of CuFeO2 (CCSD No. 00-039-0246) is cleaved as a slab model under

110

periodic boundary condition to represent the surface structure. The vacuum region is



111

set 15 Å. The surface is fully equilibrated prior to H2O2 adsorption except the bottom

112

2 layers, which are always fixed during our simulation, until the total energy of the

113

system converged to within 10–3 eV. Electronic energies are calculated using a

114

self-consistent-field (SCF) with the tolerance of 10–4 eV. The Brillouin zone

115

integration is treated with a 2 × 2 × 1 Monkhorst-Pack k-point mesh.

116

Experimental Procedure and Analysis. The heterogeneous Fenton activity of

117

CuFe-012 and CuFe-110 is evaluated by the degradation efficiency of ofloxacin

118

(OFX). Unless otherwise specified, 30 mg catalyst is added into 50 mL 10 mg/L of

119

OFX solution and the suspensions are magnetically stirred for 60 min to obtain

120

adsorption/desorption equilibrium between catalyst and OFX solution. The Fenton

121

reaction then starts upon the addition of desired amount of 30% H2O2. The reaction

122

solution is not buffered and the pH changes during the reaction process are monitored

123

by a pH meter. The pH is adjusted by a diluted aqueous solution of NaOH or HCl to

124

keep the pH within 0.3 units at the end of reaction. At given time intervals, 2 mL

125

sample is taken and filtered immediately to remove the catalyst for analysis. Then 0.1

126

mL 0.04 mol/L Na2S2O4 is added to quench the residual •OH. The concentration of

127

OFX in filtrate is determined by high performance liquid chromatography (HPLC,

128

Hitachi L-2130) with an UV-DAD detector. The chromatographic separation is

129

performed by a reverse-phase C18 column (250 mm×4.6 mm, 5 μm). The mobile

130

phase composed of 15% acetonitrile and 85% ultrapure water is acidified by 1%

131

phosphoric acid with a flow rate of 0.5 mL/min. The injection volume is 20 μL.

132

Temperature of the column chamber is maintained at 25 °C and the detection


Page 6 of 26

Page 7 of 26


133

wavelength is 288 nm. All the experiments are repeated three times and the data

134

represent the average of the triplicates with a standard deviation less than 5%.

135

Tert-butyl alcohol (TBA) and Benzoquinone are used as scavengers for •OH and •O2－,

136

respectively. The changes of H2O2 concentration during Fenton reaction is determined

137

by KMnO4 titration. The Arrhenius activation energies are obtained from the slope of

138

the logarithm of the first-order rate constants versus the inverse absolute temperature.

139

 RESULTS AND DISCUSSION

140

Reactivity of CuFeO2 with Different Exposed Facets. The catalytic performance of

141

CuFeO2 nanocube (CuFe-110) and nanoplate (CuFe-012) is compared in Figure 1A.

142

Almost no OFX degradation is observed under H2O2 oxidation alone without catalyst

143

(curve a). Both CuFe-110 and CuFe-012 are negligible in OFX adsorption (below 5%,

144

data not shown). In comparison, OFX was rapidly degraded in the CuFe-110/H2O2,

145

and the degradation rate is even faster in the CuFe-012/H2O2 (curves d and e).

146

However, both Fe2O3 and Cu2O have much lower efficiency for OFX degradation

147

(curves b and c). Besides, the leached Cu and Fe ions from CuFeO2 shows almost no

148

OFX degradation (Figure S1 of the SI) and the contribution of homogeneous Fenton

149

reaction to OFX removal is negligible when CuFeO2 is used as Fenton catalyst. Hence,

150

CuFeO2 is proven to be a promising heterogeneous Fenton catalyst. As depicted in

151

Figure S2 of the SI, the reaction condition is optimized as followed: 0.6 g/L CuFe-012,

152

0.06 mol/L H2O2 dosage. However, as shown in Figure 1B, the OFX degradation can

153

be fit well with pseudo-first-order kinetics (R2 > 0.99). The rate constant (k) of OFX

154

degradation in the CuFe-012/H2O2 is found to be 4.04 times of that in the



155

CuFe-110/H2O2, with values of 0.0408 and 0.0101 min-1, respectively. As shown in

156

Table S1 of the SI, Turn Over Frequency (TOF) of OFX degradation over CuFeO-012

157

is also two times higher than that of CuFeO-110, which is consistent with the results

158

in Figure 1. Although the same composition of CuFeO2, nanocube (CuFe-110) and

159

nanoplate (CuFe-012) exhibited different Fenton activity towards OFX degradation.

160

It was reported that the catalytic feasibility of heterogeneous Fenton catalysts was

161

governed by the thermodynamic favorability of reducing M(n+1)+ to Mn+ by H2O2.26,27

162

XRD patterns of CuFe-012 and CuFe-110 in Figure 2A match well with the standard

163

data for high pure bulk CuFeO2 with a rhombohedral structure (JCPDS card No.

164

75-2146, space group, R-3M). 28,29 XPS spectrum in Figure S3 of the SI indicates that

165

the valence states of Cu and Fe are +1 and +3 in both CuFe-012 and CuFe-110. The

166

peaks at 951.8 eV and 931.8 eV indicated in Figure S3A correspond to the Cu 2p1/2

167

and Cu 2p3/2 of Cu+, while the binding energies at 725.3 eV and 711.2 eV indicated in

168

Figure S3B are the characteristic peaks of Fe3+ with Fe 2p1/2 and Fe 2p3/2, respectively.

169

30,31

170

catalytic activity between CuFe-012 and CuFe-110 is then negligible. The surface area

171

of CuFe-012 and CuFe-110 analyzed by BET is 15.23 m2/g and 12.76 m2/g in Figure

172

S4 of the SI, respectively. Therefore, the surface area of CuFe-012 and CuFe-110 is

173

also not related to the difference in degradation rate of both Fenton system.

The contribution of element composition and their chemical states to the different

174

Exposed {012} Facets of CuFeO2 for High H2O2 Utilization Efficiency. The

175

above results show that the heterogeneous Fenton activity of CuFeO2 should be not

176

only dependent on the chemical valance of Cu, Fe and surface area. It is necessary to


Page 8 of 26

Page 9 of 26


177

investigate the reaction between H2O2 and CuFeO2 with different crystal orientation.

178

Firstly, the morphology and structure of CuFe-012 and CuFe-110 are examined by

179

SEM, TEM and HRTEM. Figure 2B and 2C depicted that two CuFeO2 architectures

180

were well-defined shape. The average width and thickness of CuFe-012 nanoplate is

181

about 1 µm and 50 nm. The lattice fringe of 0.251 nm in HRTEM is consistent with

182

{012} plane (Figure 2E), which meant the plate facet of CuFe-012 is mainly in {012}

183

crystal phase. CuFe-110 was mainly composed of cube with well-defined edges and

184

corners. The lattice fringe of 0.152 nm in HRTEM image (Figure 2F), which indicates

185

the cube facet of CuFe-110 is mainly in {110} orientation.

186

The surface structure of Cu, Fe, and O on the facets of CuFeO2 is expected to be

187

vital for its Fenton activity and the H2O2 decomposition. To confirm this anticipation,

188

the theoretical simulations of the surface structure of CuFeO2 and H2O2 adsorption on

189

the both facets is carried out in this study. The chemisorption state of H2O2 on

190

different facets is simulated to verify the effect of adsorption process on the Fenton

191

activity of CuFeO2. The simulation of CuFeO2 structure indicates there are more iron

192

and copper atoms to be exposed on the surface of {110} than that of {012} facet as

193

showed in Figure 3A and 3B. Table S2 of the SI reveals that the O-O bond length in

194

H2O2 can be greatly elongated from 1.468 Å to 3.290 Å. Long O-H-O bond (2.472 Å)

195

may inhibit electron transfer from Cu and Fe to absorbed H2O2, hence, H2O2 tends to

196

be dissociated into -OH group and passivates the {110} facet. In comparison with

197

{110} facet, Cu, Fe, and O atoms are exposed evenly on {012} facet, where the most

198

favorable configuration between H2O2 and CuFeO2 {012} facet was formed with a



199

slightly larger O-O bond length of 1.472 Å than that of free H2O2 (1.468 Å). Besides,

200

the length of O-H-O bond (1.749 Å) on CuFe-012 is smaller than that on {110} facet,

201

which also favors the H2O2 activation and •OH radical formation due to easy electron

202

transfer.32,33 The concentration of •OH during the Fenton-like reaction process was

203

determined by the reaction with dimethyl sulfoxide (DMSO).34,35 Figure S5 of the SI

204

clearly indicates that •OH was generated in both CuFe-012 and CuFe-110 Fenton

205

systems. However, the •OH amount over CuFe-012 was much higher than that over

206

CuFe-110 under the same reaction condition. It provides a direct proof of the higher

207

Fenton activity of CuFe-012 catalyst. The effect of exposed facet on Fenton

208

performance of CuFeO2 is studied by comparing the activation energy (Ea) of OFX

209

degradation according to Arrhenius equation.36,37 Figure S6 of the SI shows that OFX

210

removal efficiency increases with the reaction temperature for both FeCu-110 and

211

FeCu-012 catalysts. It means the Fenton reaction process for OFX degradation is

212

mainly governed by thermodynamics. However, as shown in Figure 4A, {012} facet

213

has a much higher H2O2 decomposition rate (0.0166 min-1) and efficiency (100% at

214

120 min) than that of {110} facet (0.0039 min-1, 50% at 120 min) at 25 oC. The

215

activation energy (Ea) of {012} and {110} facet is calculated as 22.92 and 34.52

216

kJ/mol by Arrhenius equation (Figure 4B). It agreed well with their vertical distance

217

between H2O2 and CuFeO2 surface, 1.749 Å for {012} vs. 2.472 Å for {110}

218

indicated in Figure 3C and 3D. The H2O2 utilization efficiency of {012} facet and

219

{110} facet was 65.85% and 45.75%, respectively in Figure S7 of the SI. Hence, a

220

suitable facet exposure for appropriate elongation of O-O bond in H2O2 play a key


Page 10 of 26

Page 11 of 26

221


role in determining the heterogeneous Fenton activity of CuFeO2.

222

Radicals Identification and Good Stability of CuFe-012. The electron transfer

223

process between CuFeO2 and H2O2 can generate •OH and O2•-. The ESR spectrum in

224

Figure 5A indicates a strong 4-fold characteristic peak of DMPO-•OH adducts with an

225

intensity ratio of 1:2:2:1.38,39 At the same time, a relatively weak sextet peaks of

226

DMPO-HO2•/O2•- adducts was also observed. Moreover, tert-butyl alcohol has a much

227

higher inhibition effect on OFX degradation compared with benzoquinone as shown

228

in Figure 5B. In comparison with the control experiment (no scavenger is present), the

229

OFX degradation efficiency was decreased by about 70% in the presence of 50 mM

230

tert-butyl alcohol, whereas only about 15% inhibition is observed in the presence of

231

the same amount of benzoquinone. Therefore, •OH is the dominant reactive oxygen

232

species and responsible for OFX degradation in CuFeO2 {012} facet/H2O2 system.

233

Based on the traditional Fenton mechanism, •OH is generated from the reaction Mn+ +

234

H2O2 → M(n+1)+ + •OH + OH- (Reaction 1), while HO2• is produced from the reaction

235

M(n+1)+ + H2O2 → Mn+ + HO2• + H+ (Reaction 2). The redox process should occur near

236

stoichiometrically 1:1 for an ideal Fenton catalyst. Actually, much more amount of

237

•OH

238

Cu+ in CuFeO2 are finally 100% consumed but the recycle of Fe3+/Fe2+, Cu2+/Cu+ was

239

indeed inhibited. Then, CuFeO2 nanoplates should have a poor reuse stability.

240

However, no obvious deactivation of CuFe-012 is observed in Figure 6. OFX is

241

always completely degraded in the five successive degradation experiments. The XRD

242

patterns and SEM images of CuFe-012 after 5th cycle shown in Figure S8 further

was detected than HO2• in this study. It means that the reductive species such as



Page 12 of 26

243

illustrates the stability of CuFe-012 catalyst. There was almost no change on the Cu,

244

Fe chemical valance in CuFe-012 based on XPS spectra (Figure S9 of the SI).30 Based

245

on the above results, CuFeO2 nanoplates had an excellent stability and its crystalline

246

structure did not change. There must exist an intrinsic reason for the interaction of Cu

247

and Fe within CuFeO2 during heterogeneous Fenton reaction process.

248

Discussion on the Mechanism of CuFe-012 for Efficient H2O2 Activation. The

249

concentration of leaching Cu and Fe ions from CuFe-012 are determined by ICP-MS

250

analysis. As shown in Figure S10 of the SI, there is no significant Cu ion detected

251

(below 0.30 mg/L). While the concentration of Fe ion in solution increases rapidly

252

and reaches a maximum value of 5.45 mg/L at 30 minutes and then decreases with the

253

reaction time. It indicated that Cu is stable within CuFe-012 but Fe has a release and

254

re-confinement process during the Fenton reaction. Based on the experimental results

255

and previous literature, the possible heterogeneous Fenton reaction mechanism over

256

CuFeO2 {012} facet is proposed in Figure 7. ≡ Cu+ + H2 O2 →≡ Cu2+ + OH ∙ + OH −

Reaction 3

Fe2+ + ≡→≡ Fe2+∗

Reaction 5

≡ Cu+ + ≡ Fe3+ →≡ Cu2+ + ≡ Fe2+

Reaction 7

≡ Fe3+ + H2 O2 →≡ Fe2+ + HO∙2 + H +

Reaction 4

≡ Fe2+∗ + ≡ Cu2+ →≡ Cu+ + ≡ Fe3+

Reaction 6

≡ Fe2+∗ + H2 O2 →≡ Fe3+ + OH ∙ + OH −

Reaction 8

257

During the H2O2 activation process on {012} facet, ≡Cu+ is oxidized to ≡Cu2+,

258

accompanied by the generation of •OH (reaction 3). At the same time, some ≡Fe3+ is


Page 13 of 26


259

reduced to ≡Fe2+ and HO2• is formed by reaction 4. It is worth noting that most of the

260

released Fe2+ are re-confined on CuFeO2 {012} facet via oxygen-iron bond (≡Fe2+*,

261

reaction 5). ≡Fe2+* is reported to have a much higher reductive ability than ordinary

262

Fe2+, which can induce the reduction of high valent UVI, CrVI, AsV and substituted

263

nitrobenzene.40-45 Similarly, ≡Fe2+* can reduce ≡Cu2+, yielding a Cu redox cycle

264

(reaction 6). Of course, part of ≡Fe3+ and ≡Cu+ was converted to ≡Fe2+ and ≡Cu2+ via

265

reaction 7.46 The new formed ≡Fe2+* plays an important role for the excellent

266

long-term stability of CuFe-012. As depicted in Figure 3C and 3D, H2O2 is preferably

267

absorbed on Fe sites in CuFe-012 by theoretical simulations. Due to the strong

268

electron attraction of ≡Fe3+, the -OH bond on CuFeO2 {012} facet can decrease the

269

electron density of neighboring H-O bond, resulting in the O-O bond in H2O2 to

270

become weaker. It will favor the •OH formation via the electron transfer from exposed

271

metal to H2O2 according to reaction 3 and 8.

272

It has been widely accepted that the activity of most heterogeneous Fenton catalysts

273

will decrease greatly at neutral or even alkaline condition because a small fraction of

274

H2O2 is converted into •OH radicals. In this study, CuFe-012 shows satisfied oxidation

275

efficiency for OFX degradation at a pH range of 3.2-10.1 with the best performance at

276

pH 6.5 (Figure S11A of the SI). Although the OFX removal efficiency decreases by

277

about 40% in the local pond water in comparison with the control experiment (in

278

distilled water, Figure S11B), it is because of the competitive effect of total dissolved

279

organic carbon and co-existing anions in consumption of •OH radicals. Figure S12 of

280

the SI further depicted that the zero charge point of CuFe-012 is close to pH 6. Since



Page 14 of 26

47

281

the pKa1 and pKa2 of OFX are 6.05 and 8.11 respectively,

282

adsorption to OFX removal should increase with the initial solution pH. The intrinsic

283

electron transfer between Cu and Fe, especially the new formed ≡Fe2+* species could

284

overcome the inhibited cycle of M(n+1)+/Mn+. The suitable {012} facet exposure and

285

O-O bond elongation in H2O2 can further enhance the H2O2 utilization efficiency in

286

Fenton-like reaction and OFX degradation. The findings in this study provide a deep

287

understanding on the enhanced reactivity by facets exposure, and also shed light on

288

the design of high efficient heterogeneous Fenton catalysts.

289

ASSOCIATED CONTENT

290

Supporting Information

291

Additional experimental data, such as the characterization of CuFeO2 by XRD, XPS,

292

BET; contribution of homogeneous Fenton reaction to OFX degradation caused by

293

leached Cu and Fe from CuFe-012, optimization of CuFe-012 and H2O2 dosage;

294

pseudo-first-order kinetic rate plot; TOF values; OFX adsorption experiments; H2O2

295

decomposition and utilization efficiency; and the effect of solution pH and water

296

characteristics on OFX degradation are provided in the supplementary information.

297

This material is available free of charge via the Internet at http://pubs.acs.org.

298

AUTHOR INFORMATION

299

Corresponding Authors: *Prof. Xike Tian. Phone: 86-27-67884574. Fax:

300

86-27-67884574. E-mail: [email protected].

301

Notes

302

The authors declare no competing financial interest.


the contribution of

Page 15 of 26


303

ACKNOWLEDGEMENTS

304

This work is supported by the National Natural Science Foundation of China (Grant

305

No. 41773126), the Foundation for Innovative Research Groups of the National

306

Natural Science Foundation of China (No. 41521001) and the “Fundamental Research

307

Funds for the Central Universities”.

308

REFERENCES

309

(1) Andreozzi, R.; Caprio, V.; Insola, A.; Marotta, R., Advanced oxidation processes

310 311 312

(AOP) for water purification and recovery. Catal. Today 1999, 53, (1), 51-59. (2) Bryliakov, K. P., Catalytic asymmetric oxygenations with the Environmentally benign oxidants H2O2 and O2. Chem. Rev. 2017, 117(17):11406-11459.

313

(3) Tiwari, A. J.; Morris, J. R.; Vejerano, E. P.; Jr, H. M.; Marr, L. C., Oxidation of C60

314

aerosols by atmospherically relevant levels of O3. Environ. Sci. Technol. 2014, 48,

315

(5), 2706-2714.

316 317 318

(4) Wang, J.; Bai, Z., Fe-based catalysts for heterogeneous catalytic ozonation of emerging contaminants in water and wastewater. Chem. Eng. J. 2017, 312, 79-98. (5) Ribeiro, A. R.;

Nunes, O. C.; Pereira, M. F.; Silva, A. M., An overview on the

319

advanced oxidation processes applied for the treatment of water pollutants defined

320

in the recently launched Directive . Environ. Int. 2015, 75, 33-51.

321

(6) Do, Q. C.; Kim, D. G.; Ko, S. O., Non-sacrificial template synthesis of

322

magnetic-based yolk-shell nanostructures for the removal of acetaminophen in

323

Fenton-like systems. ACS Appl. Mater. Interfaces, 2017, 9, (34), 28508–28518 .

324

(7) Munoz, M.; Pedro, Z. M. D.; Casas, J. A.; Rodriguez, J. J., Preparation of

325

magnetite-based catalysts and their application in heterogeneous Fenton oxidation

326

-A review. Appl. Catal. B:Environ. 2015, 176-177, 249-265.

327

(8) Nie, Y.; Zhang, L.; Li, Y. Y.; Hu, C., Enhanced Fenton-like degradation of

328

refractory organic compounds by surface complex formation of LaFeO3 and H2O2.

329

J. Hazard. Mater. 2015, 294, 195-200.

330

(9) Neyens, E.; Baeyens, J., A review of classic Fenton's peroxidation as an advanced 15 ACS Paragon Plus Environment


331

oxidation technique. J. Hazard. Mater. 2003, 98, (1-3), 33-50.

332

(10) Jiang, Z.; Yang, F.; Yang, G.; Kong, L.; Jones, M. O.; Xiao, T.; Edwards, P. P.,

333

The hydrothermal synthesis of BiOBr flakes for visible-light-responsive

334

photocatalytic degradation of methyl orange. J. Photoch. Photobio. A 2010, 212,

335

(1), 8-13.

336 337

(11) Bokare, A. D.; Choi, W., Review of iron-free Fenton-like systems for activating H2O2 in advanced oxidation processes. J. Hazard. Mater. 2014, 275, (2), 121-135.

338

(12) Qian, X.; Ren, M.; Zhu, Y.; Yue, D.; Han, Y.; Jia, J.; Zhao, Y., Visible light

339

assisted heterogeneous Fenton-like degradation of organic pollutant via

340

α-FeOOH/mesoporous carbon composites. Environ. Sci. Technol. 2017, 51, (7) ,

341

3993−4000.

342

(13) Jin, H.; Tian, X.; Nie, Y.; Zhou, Z.; Yang, C.; Li, Y.; Lu, L., Oxygen vacancy

343

promoted heterogeneous Fenton-like degradation of ofloxacin at pH 3.2-9.0 by Cu

344

substituted magnetic Fe3O4@FeOOH Nanocomposite. Environ. Sci. Technol. 2017,

345

51, 12699-12706.

346

(14) Tian, X.; Jin, H.; Nie, Y.; Zhou, Z.; Yang, C.; Li, Y.; Wang, Y., Heterogeneous

347

Fenton-like degradation of ofloxacin over a wide pH range of 3.6 to 10.0 over

348

modified mesoporous iron oxide. Chem. Eng. J. 2017, 328, 397–405.

349

(15) Pinto, I. S. X.; Pacheco, P. H. V. V.; Coelho, J. V.; Lorençon, E.; Ardisson, J. D.;

350

Fabris, J. D.; Souza, P. P. D.; Krambrock, K. W. H.; Oliveira, L. C. A.; Pereira, M.

351

C., Nanostructured δ-FeOOH: An efficient Fenton-like catalyst for the oxidation

352

of organics in water. Appl. Catal. B:Environ. 2012, 119-120, (120), 175-182.

353

(16) Wang, Y.; Fang, J.; Crittenden, J. C.; Shen, C., Novel RGO/α-FeOOH supported

354

catalyst for Fenton oxidation of phenol at a wide pH range using solar-light-driven

355

irradiation. J. Hazard. Mater. 2017, 329, 321-329.

356

(17) Barreiro, J. C.; Capelato, M. D.; Martinneto, L.; Bruun Hansen, H. C., Oxidative

357

decomposition of atrazine by a Fenton-like reaction in a H2O2/ferrihydrite system.

358

Water Res. 2007, 41, (1), 55-62.

359

(18) Herney-Ramirez, J.; Vicente, M. A.; Madeira, L. M., Heterogeneous

360

photo-Fenton oxidation with pillared clay-based catalysts for wastewater 16 ACS Paragon Plus Environment

Page 16 of 26

Page 17 of 26

361


treatment: A review. Appl. Catal. B:Environ. 2010, 98, (1–2), 10-26.

362

(19) Lousada, C. M.; Yang, M.; Nilsson, K.; Jonsson, M., Catalytic decomposition of

363

hydrogen peroxide on transition metal and lanthanide oxides. J. Mol. Catal.

364

A :Chem. 2013, 379, (1), 178-184.

365

(20) Stamenkovic, V. R.; Fowler, B.; Mun, B. S.; Wang, G.; Ross, P. N.; Lucas, C. A.;

366

Marković, N. M., Improved oxygen reduction activity on PtNi(111) via increased

367

surface site availability. Science 2007, 315, (5811), 493-497.

368

(21) Shiraishi, Y.; Kofuji, Y.; Sakamoto, H.; Tanaka, S.; Ichikawa, S.; Hirai, T., Effects

369

of surface defects on photocatalytic H2O2 production by mesoporous graphitic

370

carbon nitride under visible light irradiation. Acs Catal. 2015, 5, (5), 3058-3066.

371

(22) Huang, X.; Hou, X.; Zhao, J.; Zhang, L., Hematite facet confined ferrous ions as

372

high efficient Fenton catalysts to degrade organic contaminants by lowering H2O2

373

decomposition energetic span. Appl. Catal. B:Environ. 2016, 181, 127-137.

374

(23) Lousada, C. M.; Johansson, A. J.; Brinck, T.; Jonsson, M., Mechanism of H2O2

375

decomposition on transition metal oxide surfaces. J. Phys. Chem. C 2012, 116,

376

(17), 9533-9543.

377

(24) And, S. S. L.; ‡, M. D. G., Catalytic Decomposition of hydrogen peroxide on iron

378

oxide:  kinetics, mechanism, and implications. Environ. Sci. Technol. 1998, 32,

379

(10), 1417-1423.

380

(25) Long, R.; Mao, K.; Ye, X.; Yan, W.; Huang, Y.; Wang, J.; Fu, Y.; Wang, X.; Wu,

381

X.; Xie, Y., Surface facet of palladium nanocrystals: a key parameter to the

382

activation of molecular oxygen for organic catalysis and cancer treatment. J. Am.

383

Chem. Soc. 2013, 135, (8), 3200-3207.

384

(26) Dua, M.; Kumar, S.; Virk, Z. S., Wastewater treatment with heterogeneous

385

Fenton-type catalysts based on porous materials. J. Mater. Chem. 2010, 20, (41),

386

9002-9017.

387

(27) Costa, R. C. C.; Lelis, M. F. F.; Oliveira, L. C. A.; Fabris, J. D.; Ardisson, J. D.;

388

Rios, R. R. V. A.; Silva, C. N.; Lago, R. M., Novel active heterogeneous Fenton

389

system based on Fe3−xMxO4 (Fe, Co, Mn, Ni): The role of M2+ species on the

390

reactivity towards H2O2 reactions. J. Hazard. Mater. 2006, 129, (1-3), 171-178. 17 ACS Paragon Plus Environment


391

(28) Ding, Y.; Tang, H.; Zhang, S.; Wang, S.; Tang, H., Efficient degradation of

392

carbamazepine by easily recyclable microscaled CuFeO2 mediated heterogeneous

393

activation of peroxymonosulfate. J. Hazard. Mater. 2016, 317, 686-694.

394

(29) Qiu, X.; Liu, M.; Sunada, K.; Miyauchi, M.; Hashimoto, K., A facile one-step

395

hydrothermal synthesis of rhombohedral CuFeO2 crystals with antivirus property.

396

Chem. Commun. 2012, 48, (59), 7365-7367.

397

(30) Zhang, L.; Nie, Y.; Hu, C.; Qu, J., Enhanced Fenton degradation of Rhodamine B

398

over nanoscaled Cu-doped LaTiO3 perovskite. Appl. Catal. B:Environ. 2012, 125,

399

(33), 418-424.

400

(31) Lirong Lu; Zhihui Ai; Jinpo Li; Zheng, Z.; Li, Q.; Lizhi Zhang, Synthesis and

401

characterization of Fe-Fe2O3 core-shell nanowires and nanonecklaces. Cryst.

402

Growth Des. 2007, 7, (2), 459-464.

403

(32) Hirao, H.; Li, F.; Lawrence Que, J.; Morokuma, K., Theoretical study of the

404

mechanism of oxoiron(IV) formation from H2O2 and a nonheme iron(II) complex:

405

O-O cleavage involving proton-coupled electron transfer. Inorg. Chem. 2011, 50,

406

(14), 6637-6648.

407

(33) Günter Lassmann, †; ‡, L. A. E.; Fahmi Himo; Friedhelm Lendzian, A.; Lubitz†,

408

W., Electronic structure of a transient histidine radical in liquid aqueous solution: 

409

EPR continuous-flow studies and density functional calculations. J. Phys. Chem. A

410

1999, 103, (9), 8111-8116.

411

(34) And, T. A. R.; Dutta, P. K., Fenton Chemistry of FeIII-Exchanged Zeolitic

412

Minerals Treated with Antioxidants. Environmental Science & Technology 2005,

413

39, (16), 6147-6152.

414

(35) Babbs, C. F.; Steiner, M. G. Detection and quantitation of hydroxyl radical using

415

dimethyl sulfoxide as molecular probe. Methods Enzymol. 1990, 186, 137-147.

416

(36) Wang, K. Y.; Chung, T. S.; Qin, J. J., Polybenzimidazole (PBI) nanofiltration

417

hollow fiber membranes applied in forward osmosis process. J. Membrane Sci.

418

2007, 300, (1-2), 6-12.

419

(37) Brás, A. R.; Noronha, J. P.; Antunes, A. M.; Cardoso, M. M.; Schönhals, A.;

420

Affouard, F.; Dionísio, M.; Correia, N. T., Molecular motions in amorphous 18 ACS Paragon Plus Environment

Page 18 of 26

Page 19 of 26


421

ibuprofen as studied by broadband dielectric spectroscopy. J. Phys. Chem. B 2008,

422

112, (35), 11087-11099.

423

(38) Fang, G.; Gao, J.; Dionysiou, D. D.; Liu, C.; Zhou, D., Activation of persulfate by

424

quinones: free radical reactions and implication for the degradation of PCBs.

425

Environ. Sci. Technol. 2013, 47, (9), 4605-4611.

426

(39) Chen, Z.; Yin, J. J.; Zhou, Y. T.; Zhang, Y.; Song, L.; Song, M.; Hu, S.; Gu, N.,

427

Dual enzyme-like activities of iron oxide nanoparticles and their implication for

428

diminishing cytotoxicity. Acs Nano 2012, 6, (5), 4001-4012.

429

(40) Stachowicz, M.; Hiemstra, T.; Riemsdijk, W. H. V., Multi-competitive interaction

430

of As(III) and As(V) oxyanions with Ca2+, Mg2+, PO43−, and CO32− ions on

431

goethite. J. Colloid Interf. Sci. 2008, 320, (2), 400-414.

432

(41) Chakraborty, S.; Favre, F.; Banerjee, D.; Scheinost, A. C.; Mullet, M.; Ehrhardt, J.

433

J.; Brendle, J.; Vidal, L.; Charlet, L., U(VI) sorption and reduction by Fe(II)

434

sorbed on montmorillonite. Environ. Sci. Technol. 2010, 44, (10), 3779-3785.

435 436 437

(42) Williams, A. G.; Scherer, M. M., Kinetics of Cr(VI) reduction by carbonate green rust. Environ. Sci. Technol. 2001, 35, (17), 3488-3494. (43) Latta,

D. E.; Bachman, J. E.; Scherer, M. M., Fe electron transfer and atom

438

exchange in goethite: influence of Al-substitution and anion sorption. Environ. Sci.

439

Technol. 2012, 46, (19), 10614-10623.

440

(44)

Islam, F. S.; Gault, A. G.; Boothman, C.; Polya, D. A.; Charnock, J. M.;

441

Chatterjee, D.; Lloyd, J. R., Role of metal-reducing bacteria in arsenic release

442

from Bengal delta sediments. Nature 2004, 430, (6995), 68-71.

443

(45) Mikalsen, A.; Capellmann, M.; Alexander, J., The role of iron chelators and

444

oxygen in the reduced nicotinamide adenine dinucleotide phosphate-cytochrome

445

P450 oxidoreductase-dependent chromium(VI) reduction. Analyst 1995, 120, (3),

446

935-938.

447

(46) Feng, Y.; Wu, D.; Deng, Y.; Zhang, T.; Shih, K., Sulfate Radical-mediated

448

degradation

of

sulfadiazine

by

CuFeO2

rhombohedral

449

peroxymonosulfate: synergistic effects and mechanisms. Environ. Sci. Technol.

450

2016, 50, (6), 3119-3127. 19 ACS Paragon Plus Environment

crystal-catalyzed


451

(47) Peres, M. S.; Maniero, M. G.; Guimarães, J. R., Photocatalytic degradation of

452

ofloxacin and evaluation of the residual antimicrobial activity. Photochemical &

453

Photobiological Sciences Official Journal of the European Photochemistry

454

Association & the European Society for Photobiology 2015, 14, (3), 556-562.

455


Page 20 of 26

Page 21 of 26


456 457

Figure Captions

458

Figure 1. OFX degradation under different conditions (A): (a) H2O2 oxidation alone,

459

(b) Fe2O3/H2O2, (c) Cu2O/H2O2, (d) CuFe-110/H2O2, (e) CuFe-012/H2O2; and (B) the

460

pseudo-first-order kinetic rate plot of OFX degradation in CuFe-110/H2O2 and

461

CuFe-012/H2O2. (Reaction condition: [OFX]=10 mg/L, pH=6.53, [catalyst]=0.6 g/L,

462

[H2O2]=0.06 mol/L, T=25℃)

463

Figure 2. XRD patterns of CuFe-110 and CuFe-012 (A); SEM image of CuFe-110 (B),

464

CuFe-012 (C) and the corresponding TEM images (inset); (D) SAED pattern of

465

CuFe-012; HRTEM image of CuFe-012 (E) and CuFe-110 (F).

466

Figure 3. The optimized surface structures of CuFeO2 catalyst: (A) CuFe-012 and (B)

467

CuFe-110; (C) H2O2 adsorption on CuFe-012 and (D) H2O2 adsorption on CuFe-110.

468

Figure 4. H2O2 decomposition as a function of reaction time over CuFe-110 and

469

CuFe-012 (A) Calculation of activation energy for CuFe-110 and CuFe-012 by the

470

plot of lnk against 1/T for a range of temperatures (B). (Reaction condition:

471

[OFX]=10 mg/L, [catalyst]=0.6g/L, [H2O2]=0.06 mol/L, pH=6.53, T=25℃)

472

Figure 5. ESR spectrum of DMPO-•OH and DMPO-O2•- in CuFe-012/H2O2 system

473

(A) using DMPO as radical trapping agents; (B) Effects of radical scavengers on OFX

474

degradation.

475

Figure 6. Stability of CuFe-012 in the multicycle degradation of OFX in the presence

476

of H2O2.

477

Figure 7. Proposed heterogeneous Fenton reaction mechanism over CuFe-012.

478 21 ACS Paragon Plus Environment


479 480

481 482

Figure 1. OFX degradation under different conditions (A): (a) H2O2 oxidation alone,

483

(b) Fe2O3/H2O2, (c) Cu2O/H2O2, (d) CuFe-110/H2O2, (e) CuFe-012/H2O2; and (B) the

484

pseudo-first-order kinetic rate plot of OFX degradation in CuFe-110/H2O2 and

485

CuFe-012/H2O2. (Reaction condition: [OFX]=10 mg/L, pH=6.53, [catalyst]=0.6 g/L,

486

[H2O2]=0.06 mol/L, T=25℃)

487


Page 22 of 26

Page 23 of 26


488 489

Figure 2. XRD patterns of CuFe-110 and CuFe-012 (A); SEM image of CuFe-110 (B),

490

CuFe-012 (C) and the corresponding TEM images (inset); (D) SAED pattern of

491

CuFe-012; HRTEM image of CuFe-012 (E) and CuFe-110 (F).

492 493

Figure 3. The optimized surface structures of CuFeO2 catalyst: (A) CuFe-012 and (B)

494

CuFe-110; (C) H2O2 adsorption on CuFe-012 and (D) H2O2 adsorption on CuFe-110.



495 496

Figure 4. H2O2 decomposition as a function of reaction time over CuFe-110 and

497

CuFe-012 (A) Calculation of activation energy for CuFe-110 and CuFe-012 by the

498

plot of lnk against 1/T for a range of temperatures (B). (Reaction condition:

499

[OFX]=10 mg/L, [catalyst]=0.6g/L, [H2O2]=0.06 mol/L, pH=6.53, T=25℃)

500

501 502

Figure 5. ESR spectrum of DMPO-•OH and DMPO-O2•- in CuFe-012/H2O2 system

503

(A) using DMPO as radical trapping agents; (B) Effects of radical scavengers on OFX

504

degradation.

505


Page 24 of 26

Page 25 of 26


506

507 508

Figure 6. Stability of CuFe-012 in the multicycle degradation of OFX in the presence

509

of H2O2.

510

511 512

Figure 7. Proposed heterogeneous Fenton reaction mechanism over CuFe-012.

513 514 515



516

Table of Contents graphic

517


Page 26 of 26

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2

Recommend Documents