Pentlandite from Microalgae: High

Subscriber access provided by UNIV OF DURHAM

Article

Fe-N-Graphene Wrapped Al2O3/Pentlandite from Microalgae: High Fenton Catalytic Efficiency from Enhanced Fe3+ Reduction Jianqing Ma, Lili Xu, Chensi Shen, Yuezhong Wen, Chun Hu, and Weiping Liu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03412 • Publication Date (Web): 12 Feb 2018 Downloaded from http://pubs.acs.org on February 12, 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.

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

Page 1 of 30

Environmental Science & Technology

Fe-N-Graphene Wrapped Al2O3/Pentlandite from Microalgae: High Fenton Catalytic Efficiency from Enhanced Fe3+ Reduction

Jianqing Ma,†Lili Xu,†Chensi Shen,‡Yuezhong Wen,*,†Chun Hu,*,§Weiping Liu†

†

MOE Key Laboratory of Environmental Remediation & Ecosystem Health, College

of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China ‡

College of Environmental Science and Engineering, Donghua University, Shanghai

201620, China §

Key Laboratory of Drinking Water Science and Technology, Research Center for

Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

Word counts: 5259 words (text and figures, excluding references)

1

ACS Paragon Plus Environment


Table of Contents Art

calcination

Fe, Al, Ni aniline polymerizing Chlorella vulgaris

2


Page 2 of 30

Page 3 of 30


1

ABSTRACT

2

Efficient cycling of Fe3+/Fe2+ is a key step for the Fenton reaction. In this

3

exploration, from microalgae, we have prepared a novel Fe-N-graphene wrapped

4

Al2O3/pentlandite composite which showed high Fenton catalytic ability through

5

accelerating of Fe3+ reduction. The catalyst exhibits high activity, good reusability

6

along with stability, and wide adaptation for the organics degradation under neutral

7

pH. High TON and H2O2 utilization efficiency have also reached by this catalyst.

8

Characterization results disclose a unique structure that the layered Fe-N-graphene

9

structure tightly covers on Al2O3/pentlandite particles. Mechanistic evidences suggest

10

that the accelerated Fe3+/Fe2+ redox cycle originates from the enhanced electron

11

transfer by the synergistic effect of Fe, Ni and Al in the catalyst, and it causes the low

12

H2O2 consumption and high •OH generation rate. Moreover, organic radicals formed

13

in the Fenton process also participate in the Fe3+ reduction, and this process may be

14

accelerated by the N doped graphene through a quick electron transfer. These findings

15

stimulate an approach with great potential to further extend the synthetic power and

16

versatility of Fenton catalysis through N doped graphene in catalysts.

17

Key words: Fenton reaction, microalgae, N doped graphene, electron transfer

18

3



19

INTRODUCTION

20

Fenton reaction is an effective and relatively low cost technology which has shown

21

immense popularity in organic synthesis and environmental protection.1-3 It usually

22

requires stoichiometric amounts of transition metals, particularly iron, and in such a

23

way that a large amount of waste is formed.4 Recently the reusable heterogeneous

24

catalytic Fenton reaction systems has gained significant attention, and intense

25

research efforts have been dedicated to develop highly efficient Fe-based Fenton

26

catalysts.5-7 However, most of Fe-based Fenton catalysts use a large amount of H2O2

27

and their oxidation efficiencies at pH > 4 are far from satisfactory8, 9. Consequently

28

the development of highly efficient Fe-based Fenton catalysts with high utilization

29

efficiency of H2O2 and extensive working pH range, especially at neutral pH values

30

and room temperature, is an attractive and challenging subject in environmental

31

application.

32

Fe-based Fenton catalytic reaction basically consists of the oxidation of Fe2+ to Fe3+

33

along with the •OH generation and the reduction of Fe3+ to Fe2+. The efficient cycling

34

of Fe3+/Fe2+ plays a significant role.10 However, Fe3+/Fe2+ cycling is blisteringly

35

interrupted by the slow step of H2O2 reduction of Fe3+ to Fe2+ (rate constants:

36

0.001-0.02 M-1s-1).11 In addition, if H2O2 is decomposed to O2 or superoxide radical

37

(O2•-), the ineffective and excessive consumption of H2O2 will transpire.12

38

Interestingly, a series of studies have found that the Fenton catalytic activity can be

39

dramatically enhanced by the complexation of transition metal ions with

40

phthalocyanine, porphyrin, phenols, pyridine, organic acids and other organic 4


Page 4 of 30

Page 5 of 30


41

chelating agents.13-16 The complexation with these ligands not only promotes the

42

redox cycling of the metal but also inhibits the conversion of H2O2 to O2, leading to

43

the improved utilization efficiency of H2O2. However, the recoveries of these

44

chelating agents are extravagant since they all become soluble in water. But these

45

findings provide a new strategy for designing heterogeneous Fenton catalyst with

46

M-N-aromatic ring or M-O-aromatic ring as electron-transfer mediators (ETM),

47

which will facilitate the electron transfer and thereby increase the Fenton reaction

48

efficiency.17

49

The current state-of-the-art M-Nx-C catalysts have showed great catalytic activity

50

and stability for the oxygen reduction reaction.18-21 Recently, we have confirmed that

51

M-N-C materials could also be used as efficient heterogeneous Fenton catalysts.22 In

52

the present study we represent a new approach towards the preparation of

53

Fe-N-graphene wrapped Al2O3/pentlandite using microalgae as carbon precursor, and

54

the acquired composite has performed high activity, good reusability and stability for

55

organics degradation. Microalgae are biological resources, which are affordable,

56

plentiful and found in various water bodies throughout the world. Their utilization

57

such as biomass energy and nutrients stripper from the sewage is extremely

58

meaningful from both economical and environmental perspectives.23, 24 Besides, they

59

could serve as a natural template for fabricating function materials with a hollow

60

porous carbon matrix.25 Therefore, we used a microalgae with high activity of metal

61

binding26 to prepare the effective Fenton catalyst with unique layered N doped

62

graphene and Fe-N complex structure. Synergistic effect of Fe, Ni and Al in this 5



Page 6 of 30

63

catalyst was observed, leading to the low H2O2 consumption and high •OH generation

64

rate. Additionally, organic radicals formed in the Fenton process also facilitate the

65

Fe3+ reduction, and this process may be accelerated by the N doped graphene through

66

a quick electron transfer and finally causing a high Fenton catalytic efficiency.

67

MATERIALS AND METHODS

68

Chemicals

and

Reagents.

FeCl3·6H2O,

Al(NO3)3·9H2O,

Ni(NO3)2·6H2O,

69

FeSO4·7H2O, sodium borohydride (NaBH4), ammonium peroxydisulfate (APS),

70

aniline, phenol and 30% (w/w) H2O2 were provided by Sinopharm Chemical Reagent

71

Co., Ltd. (Shanghai, China). C. I. Acid Red 73 (AR 73) was obtained from Gracia

72

Chemical Technology Co., Ltd. (Chengdu, China). 5,5-dimethyl-1-pyrroline-N-oxide

73

(DMPO) was purchased from Sigma-Aldrich. All chemicals were analytical grade

74

reagents and were used without further purification. Chlorellavulgaris (CV) were

75

originally obtained from Freshwater Algae Culture Collection of the Institute of

76

Hydrobiology (China), and its culture conditions were expatiate in the supporting

77

information. The deionized water used in this study was produced using a UPK/UPT

78

ultrapure water system.

79

Preparation of the catalyst. Chlorella vulgaris (CV), a sphere-shaped algae with a

80

uniform size of 2 µm in diameter, was firstly collected and used as the the precursor

81

of carbon sphere. Typically, 0.1 g dried CV and 0.5 mL aniline were dispersed in 0.5

82

M HCl solution. The suspension was kept below 10 °C, and APS (1.141 g) and

83

transition metal precursors (0.2162 g FeCl3·6H2O, 0.2626 g Al(NO3)3•9H2O and

84

0.1454 g Ni(NO3)2•6H2O) were added. After stirring for 24 hours, water in the 6


Page 7 of 30


85

suspension was removed using a vacuum rotatory evaporator. The residue was

86

subsequently heated at 900 ºC in a nitrogen atmosphere for 4 h. Moreover, the

87

obtained solid was dispersed in a 0.5 M H2SO4 solution at 80 ºC for 8 h to remove

88

fluctuating and sluggish species. The catalyst was collected through centrifugation

89

with a speed of 6000 rpm. After thoroughly washed by water, the catalyst was dried in

90

an oven at 50 ºC and donated as Fe-N/pentlandite/Al2O3/C (Fe-N-graphene wrapped

91

Al2O3/pentlandite). The metal contents of Fe, Ni and Al of the obtained catalyst are

92

14.0, 9.86 and 34.9 mg/g, respectively.

93

Characterization methods. The morphology of the catalyst was observed by a

94

Tecnai G2 F20 S High resolution Transmission electron Microscope (FEI, USA)

95

equipped with high angle annular dark field (HAADF) and energy dispersive X-ray

96

(EDX) analysis detectors. X-ray diffraction (XRD) spectra were collected on a

97

XRD-6000 X-ray diffractometer (Shimadzu, Japan) with a Cu Kα radiation (λ =

98

1.5406 Å) over a 2θ range of 10–60◦. X-ray photoelectron spectroscopy (XPS) was

99

collected on an ESCALAB 250Xi spectrometer (Thermo Scientific, UK) with a

100

monochromatic Al Kα source (1486.6 eV), and all binding energies were referenced

101

to the C 1s peak at 284.8 eV. X-ray adsorption near-edge structure (XANES) of the

102

Fe, Ni and Al L-edge was measured using the TEY mode at the BL08U beamline, and

103

Small-angel X-ray scattering (SAXS) 2D scattering patterns were obtained from the

104

BL16B1 beamline of the Shanghai Synchrotron Radiation Facility (SSRF).

105

Performance tests of the catalyst. The performance of the as-prepared catalyst was

106

evaluated by degradation of phenol and AR 73. Unless more specified, the 7



107

degradation experiments were carried out in a conical flask (250 mL). Catalysts were

108

dispersed into 100 mL aqueous solution of AR 73 (50 mg/L) or phenol (30 mg/L).

109

The degradation reaction was initiated by adding 2.0 mL of H2O2 (2.0 M) with a

110

constant stirring of 150 rpm. At predetermined time intervals, aqueous phase samples

111

(2.5 mL) were withdrawn and immediately filtered (0.22 µm) to remove the catalyst

112

solids. The concentrations of AR 73 and phenol were analyzed using a Shimadzu

113

UV-2401PC UV-Vis spectrometer (Tokyo, Japan) at 508 nm and a Waters® e2695

114

reverse-phase HPLC coupled with a Waters® 2998 photodiode array detector

115

(Milford, MA, USA), respectively. Specific detection conditions for phenol and other

116

organics are listed in Table S1. After degradation, the catalyst was collected by

117

centrifugation and dried at 50 °C，and then put into another cycle of use to test its

118

stability and reusability.

119

Total organic carbon (TOC) analysis was performed using a Shimadzu TOC-VCPH

120

(Tokyo, Japan). Fe, Al and Ni contents were monitored by an ELAN DRC-e

121

inductively coupled plasma mass spectrometry (ICP-MS, Perkin-Elmer). H2O2 was

122

measured using the DPD method reported by Bader et al.27 Reactive oxygen species

123

were detected by electron spin resonance (ESR) spectroscopy using DMPO as a spin

124

trap agent on a Bruker model ESP 300E electron paramagnetic resonance

125

spectrometer. The surface Fe2+ on the catalyst was determined using a phenanthroline

126

spectrophotometric method28. Cyclic Voltammetry Measurements were performed

127

using CHI Electrochemical Station (Model 750b) in a conventional three-electrode

128

electrochemical cell. More detailed analytical methods were described in Test S2-S4. 8


Page 8 of 30

Page 9 of 30


129

RESULTS AND DISCUSSION

130

Morphology and structure. The morphology of the catalysts was observed by

131

HAADF-STEM maps (Figure 1a and 1b). Compared with original CV (Figure S1), the

132

particle size of the catalyst still keeps at about 2 µm but the shape becomes irregular.

133

It can be seen that some small bright particles within cloudy agglomerates are

134

observed. Most of them have a size between 30 and 90 nm but transpire together with

135

smaller particles of 5-10 nm size. The distributions of Fe and Ni are consistent and

136

concentrated on the areas of these particles, while Al is more homogeneous

137

distributed in the image.

138

XRD analysis has confirmed the existence of well-developed crystal pentlandite ((Fe,

139

Ni)9S8) and Al2O3 phases (Figure S2). Therefore, the concentrated O distribution

140

which is similar to that of S can be ascribed to the existence of SO42- , which is

141

introduced during the last acid acid treatment procedure and verified by the XPS

142

spectrum (Figure S3d). Small-angel X-ray scattering 2D scattering patterns show a

143

circular shape, indicating a crystalline nature of the catalyst (Figure 1c). In addition,

144

the HRTEM image shows crystalline structures with interplanar spacing of 1.78 Å and

145

1.25 Å, which can be assigned to the (440) and (800) planes of pentlandite structure

146

(Figure 1d and 1e). At the edge of the particle, graphitic carbon with a thickness of

147

about 5 nm are for formed due to the carbonization of polyaniline-metal complex.18

148

Its chemical structure was also analyzed using XPS and XANES techniques. N was

149

detected on the catalyst surface by XPS, and its 1s peak was fitted to pyridinic N

150

(398.5 eV), Fe-Nx (400.5 eV), and graphitic N (403.9 eV). The Fe-Nx and pyridinic N 9



Page 10 of 30

151

were found to be the dominant components (Figure 2a), indicating that nitrogen in a

152

graphite-like structure and the Fe-N coordination state in catalyst was formed. Fe

153

L-edge XANES in Figure 2b also confirmed the structure of Fe-N, as the spectra of

154

the catalyst was more parallel to that of pyrrolic Fe-N4 (calcined). Similar Fe-Nx

155

centers after heat treatment showing high catalytic activity were confirmed in our

156

previous report22, therefore, they are very likely the active sites for the Fenton

157

reaction in this study. XPS spectra of Fe 2p (Figure S3) exhibit two peaks at 711.7 and

158

724.9 eV, which are assigned to Fe 2p3/2 and Fe 2p1/2, respectively, indicating that Fe

159

exists in common Fe3+ oxidation state. Besides, the spectra of Ni 2p and Al 2p show

160

the characteristic peaks of Ni2+ ion and Al2O3 phase.

161

In order to further scrutinize the catalyst structure, we prepared catalysts with

162

different

metal

ions

as

shown

in

Figure

S4.

163

Fe-N/pentlandite/Al2O3/C (it is also FeAlNi-C) shows the best dispersion of particles.

164

Succeeding, we explored the BET surface areas of these catalysts as shown in Table

165

S2. Supplement of only Fe precursor showed high BET, about 336.056 m2/g. However,

166

addition of Al or Ni precursors can decrease BET surface areas of catalysts, especially

167

for Ni, it can monumentally diminish BET surface area in all samples. These

168

consequences maybe attributed to the following reasons. (1) According to our

169

previous analysis, Fe is mainly complexed with N in graphene, so in the condition of

170

only Fe precursor addition, Fe-C catalyst has high BET surface area. (2) Ni

171

substantially forms pentlandite particles with Fe and S elements, leading to the

172

shrinakge in BET surface area. (3) Al2O3 is homogeneously coated on the surface of 10


It

can

be

seen

that

Page 11 of 30


173

metal oxides. Compared with Fe-C and Ni-C, the addition of Al precursor only caused

174

a small BET decrease. Based on these results, we have given structure schematic of

175

Fe-N/pentlandite/Al2O3/C in Figure 1f.

176

Catalytic performance. Phenol is a simple and common organic compound with

177

one aromatic ring and also an important intermediate for the degradation of aromatic

178

hydrocarbons with higher molecule weight. AR 73 represents one class of complex

179

organic compounds with more than 2 aromatic rings and indigent biodegradation

180

property. Such kind of an interpretation is consequential to make the utilization of

181

catalysts more representative in the organic pollutant remediation. As shown in Figure

182

3, the degradation efficiency of AR 73 and phenol was up to 95% after 30 min, while

183

the adsorption accounted for less than 30% of the organics removal. Moreover, the

184

removals of TOC were 76.0% (phenol) and 69.9% (AR 73), respectively. The low

185

TOC removal due to adsorption in Figure S5 further indicates that most of the

186

organics decrease is the effect of catalytic degradation. The accumulated turnover

187

numbers (TON) reached 1955.7 (for phenol) and 449.8 (for AR 73), which are much

188

higher than most Fe-based Fenton catalysts reported.29-31, insinuating that the fabulous

189

catalytic ability for the Fenton reaction. Other typical refractory pollutants, such as

190

atrazine, bisphenol A (BPA), 2,4,5-trichlorophenol (2,4,5-TCP), 4-chlorophenol

191

(4-CP), 4-hydroxyphthalic acid (4-HPA), 4-methylphthalic acid (4-MPA) and several

192

kinds of dyes were also tested in this study, and over 85% removal at 60 min was

193

reached for all these organics (Figure S6), indicating a wide substrate adaptation for

194

this novel Fenton system. 11



Page 12 of 30

195

Subsequently, we also examined the stability and reusability of the catalyst, which

196

are crucial performance metrics for the cost-effective industrial processes. During the

197

degradation process, the pH drops from 6.8 to 4.4, and metal ions thereby leach to the

198

solution. The concentrations of Fe, Ni and Al are only 0.02, 0.35 and 0.0008 mg/L

199

after 30 min, respectively, thus the homogeneous Fenton reaction induced by the

200

leaching ions are limited (Figure S7). When the initial pH drops to 3, the leaching

201

metals slightly increase, but they are all lower than the 0.8 mg/L (Figure S8),

202

manifesting the efficiency as well as stability in a wide pH range. It can be seen from

203

Figure S9 that Fe-N/pentlandite/Al2O3/C was capable to be reused for at least twelve

204

cycles and the reused catalyst almost remained in the corresponding catalytic activity.

205

The stability of the catalyst was further investigated by HAADF-STEM and the result

206

was shown in Figure S10. There is nothing revelatory differences between the two

207

images, indicating no apparent change in the morphology during the reaction.

208

Supplementary, its good chemical stability was confirmed by XPS measurements on

209

the catalyst before and after twelve cycles (Figure S3). The spectra of Fe 2p slightly

210

shifted from 711.7 to 711.1 eV, suggesting a transformation of Fe3+ to Fe2+ on the

211

catalyst surface.32 The XPS spectra of Ni 2p and Al 2p on the surface of the spent

212

catalyst were almost the same as it was on the surface of the fresh one, suggesting that

213

the valences of these elements on the surface of the catalyst were not changed in the

214

reaction.

215

Fe-N/pentlandite/Al2O3/C indicated that the catalyst has an excellent long-term

216

stability.

Good

catalytic

performance

and

12


no

deactivation

of

Page 13 of 30


217

Synergistic

effects

of

metal

ions.

Compared

with

control

samples,

218

Fe-N/pentlandite/Al2O3/C exhibited the highest catalytic activity (Figure S11), and it

219

suggested that the synergistic effects of Fe, Al and Ni were existed. In order to

220

understand more about them, we performed a kinetic study on the catalytic

221

decomposition of H2O2 by different catalysts in the absence of pollutants (Figure S12).

222

Interestingly, the rate of H2O2 decomposition in the presence of Fe-C was the highest.

223

The addition of Al precursor or Ni precursor can decrease the rate of H2O2

224

decomposition. When in the presence of Fe, Al and Ni precursors, which is also

225

Fe-N/pentlandite/Al2O3/C, the catalyst showed the lowest rate of H2O2 decomposition.

226

Further, the active oxygen species was detected by ESR technique (Figure S13).The

227

ESR spectrum in the presence of Fe-N/pentlandite/Al2O3/C displayed a 4-fold

228

characteristic peak of the typical DMPO-HO• adduct with an intensity ratio of 1:2:2:1

229

in the aqueous solution, but no signal was found in the methanol solution, confirming

230

the •OH radical mechanism of this Fenton reaction33. Furthermore, its intensity was

231

much higher than that of FeAl-C, FeNi-C, AlNi-C, Fe-C, Al-C and Ni-C catalytic

232

systems, indicating the higher •OH yielding than the reference catalysts.

233

In many reported Fe3+-initiated Fenton systems, H2O2 takes part in both the

234

reduction and the oxidation reactions with the production of HO• (reactive oxygen

235

species for organics removal) and HO2• or O2 (ineffective consumption of H2O2)5, 34.

236

It is believed that Ni2+ and its oxides are incompetent to decompose H2O2,35 which is

237

consistent with our results that Ni-C has the lowest H2O2 decomposition rate.

238

However, the addition of Ni into the goethite structure could facilitate the reduction of 13



239

Fe3+ to Fe2+, therefore the reduction of H2O2 generating HO• could be accelerated.36

240

Similar synthetic effects of Fe and Ni are also reported in Fe-Ni nanoparticles and

241

Fe/Ni/SBA-15.35, 37 The surface sites occupation of Ni in the present study impedes

242

the H2O2 oxidation to noneffective HO2• or O2, and more H2O2 is therefore adsorbed

243

on the Fe-N sites and reduced to HO•, leading to its high utilization efficiency (66.3%

244

for AR 73 removal). On the other hand, Al2O3 can act as a Lewis acid which could

245

facilitate the reduction of the ferric ion by attracting the electron density from the iron

246

center and destabilizing the Fe3+ state.38 Therefore, the synergistic effects of metal

247

ions can be ascribed to the acceleration of Fe3+ reduction and the increased •OH

248

production for the organics degradation. The cyclic voltammetry curves of catalyst

249

can directly show the reduction/oxidation of Fe2+/Fe3+ in catalysts.39 Compared with

250

FeNi-C and FeAl-C, Fe-N/pentlandite/Al2O3/C in Figure S14a showed a pair of strong

251

reversible redox peaks around 0.40 V, and the peak separation was about 50 mV,

252

indicating a small electron transfer barrier, which further confirmed the synergistic

253

effects of metal ions.

254

Enhanced activity by accelerating Fe3+ reduction. To further explore the cycling

255

of Fe3+/Fe2+ in Fenton catalytic reactions, we examined the concentrations of Fe2+ on

256

the catalyst in the presence of H2O2. It can be seen that in the presence of catalyst and

257

H2O2 without AR 73, or in the presence of catalyst and AR 73, the concentrations of

258

Fe2+ were very low (Figure 4a). However, the concentrations of Fe2+ were

259

significantly enhanced with AR 73 degradation in the catalyst suspension, manifesting

260

the importance of organics in the Fe3+ reduction. The produced Fe2+ concentration 14


Page 14 of 30

Page 15 of 30


261

increased with the reaction time and reached to the maximum level at 15 min, then

262

decreased due to the increase of Fe2+ consumption in the degradation process.

263

According to the Lin & Gurol mechanism40, the Fenton reaction initiates with the Fe3+

264

reduction to Fe2+ by H2O2, which was facilitated by the coordination with N and the

265

synergistic effects of Ni and Al in this study, and then Fe2+ rapidly reacts with H2O2 to

266

generate active •OH and triggers a series of steps. As no HO2· radicals are observed

267

by ESR and the reduction of Fe3+ by H2O2 is quite low, the high efficiency of Fe2+

268

production only can be ascribed to the reduction by reactive organic radicals (R·, the

269

product of HO· attacking to organics).5 To demonstrate this hypothesis we performed

270

two quenching study using ethanol and Na2CO3 as HO· scavengers, and found they

271

inhibited the AR 73 removal in Figure S15. The quenching of HO· could hinder the

272

formation of ·R, resulting in the decrease of R· in the system. The decreased ·R

273

further caused the decrease of Fe2+ on the catalyst surface (Figure 4b), revealing that

274

R· was really the key electron donor for Fe3+ reduction.41

275

Yao et al. found that graphene overlayers on metals can facilitate the CO oxidation

276

with lower apparent activation energy by the

277

accumulation.42 In addition, graphene43 and a π-conjugated carbon material44 could

278

also transfer electron to Fe in the photo-Fenton or Fenton system. In the present study,

279

the doped N atoms in graphene act as ligands to modify the redox properties by

280

ligand-field effects.45 Besides, graphene structure can attract organics from bulk

281

solution to the catalyst surface (compared with FeAlNi in Figure S11), which

282

facilitates the reaction of HO· and organics to generate R·. Lyu et al.41 proposed a 15


graphene-induced electron


283

galvanic-like cells mechanism that H2O2 reduced at the electron-rich Cu center

284

(cathode) and the R· oxided on the electron-deficient region (anode) through the

285

delivery of the electron from R· to the cathode during the reaction. For the M-N-C

286

catalyst, the carbon atoms adjacent to N possess high positive spin density and atomic

287

charge density by DFT and experimental observations.46 Based on this, it is

288

reasonable to speculate that once R· is produced, it could immediately add to

289

graphene region which is adjacent to N atoms through free radical addition47, leading

290

to enhanced electron transfer from organic radical to Fe3+ for its quick reduction (as

291

illustrated in Figure 5). Therefore, we reasoned that Fe-N-graphene wrapped

292

Al2O3/pentlandite structures could decrease the Fenton reaction barrier, accelerate the

293

efficient cycling of Fe3+/Fe2+, and finally result the high Fenton catalytic efficiency.

294 295

ASSOCIATED CONTENT

296

Supporting Information

297

Details regarding the Experimental Section and calculation of the accumulated

298

turnover numbers and the utilization efficiency of H2O2. Table S1 lists the HPLC

299

conditions for organics detection, while Table S2 shows BET specific areas of

300

different samples. Figure S1-S15: picture of CV, XRD pattern of the catalyst, XPS

301

spectra, HAADF-STEM images of different catalysts, TOC removal efficiency,

302

degradation of other dyes and refractory organics, pH change and metal leaching,

303

reusability tests, HAADF-STEM image of the used catalyst, degradation and

304

adsorption tests using different catalysts, H2O2 decomposition tests, ESR spectra and 16


Page 16 of 30

Page 17 of 30


305

cyclic voltammetry curves, the effect of scavengers on AR 73 removal. This material

306

is available free of charge on the Internet at http://pubs.acs.org.

307 308

AUTHOR INFORMATION

309

Corresponding Author

310

*Phone: +86 571 8898 2421; fax: +86 571 8898 2421.

311

E-mailaddress: [email protected] (Y.W.) and [email protected](C.H.)

312

Notes

313

The authors declare no competing financial interest.

314

ACKNOWLEDGMENTS

315

We thank 863 Research Project (2013AA065202), Major Program of National Natural

316

Science Foundation of China and the National Natural Science Foundation of China

317

(No. 21407021) for financial support. We also thank the staff at beamlines BL08U

318

and BL16B1 at the Shanghai Synchrotron Radiation Facility (SSRF) for providing the

319

beam time and data analysis.

320

References 1.

Ito, S.; Mitarai, A.; Hikino, K.; Hirama, M.; Sasaki, K., Deactivation reaction in

the hydroxylation of benzene with Fenton's reagent. J. Org. Chem. 1992, 57, (25), 6937-6941. 2.

Casero, I.; Sicilia, D.; Rubio, S.; Pérez-Bendito, D., Chemical degradation of

aromatic amines by Fenton's reagent. Water Res. 1997, 31, (8), 1985-1995. 3.

Peng, J.; Shi, F.; Gu, Y.; Deng, Y., Highly selective and green aqueous–ionic 17



liquid biphasic hydroxylation of benzene to phenol with hydrogen peroxide. Green Chem. 2003, 5, (2), 224-226. 4.

Pang, S.Y.; Jiang, J.; Ma, J., Oxidation of sulfoxides and arsenic (III) in corrosion

of nanoscale zero valent iron by oxygen: evidence against ferryl ions (Fe (IV)) as active intermediates in Fenton reaction. Environ. Sci. Technol. 2010, 45, (1), 307-312. 5.

Navalon, S.; Alvaro, M.; Garcia, H., Heterogeneous Fenton catalysts based on

clays, silicas and zeolites. Appl. Catal. B-environ. 2010, 99, (1), 1-26. 6.

Liu, W.; Xu L.; Li X.; Chen Si.; Rashid S.; Wen, Y., High-dispersive FeS2 on

graphene oxide for effective degradation of 4-chlorophenol. RSC Adv. 2015, 5, 2449-2456. 7.

Barreiro, J. C.; Capelato, M. D.; Martin-Neto, L.; Bruun Hansen, H. C., Oxidative

decomposition of atrazine by a Fenton-like reaction in a H2O2/ferrihydrite system. Water Res. 2007, 41, (1), 55-62. 8.

Plata, G. B. O. D. L.; Alfano, O. M.; Cassano, A. E., Decomposition of

2-chlorophenol employing goethite as Fenton catalyst. I. Proposal of a feasible, combined reaction scheme of heterogeneous and homogeneous reactions. Appl. Catal. B-environ. 2010, 95, (1–2), 1-13. 9. Zhang, J.; Zhuang, J.; Gao, L.; Zhang, Y.; Gu, N.; Feng, J.; Yang, D.; Zhu, J.; Yan, X., Decomposing phenol by the hidden talent of ferromagnetic nanoparticles. Chemosphere 2008, 73, (9), 1524–1528. 10. Qin, Y.; Song, F.; Ai, Z.; Zhang, P.; Zhang, L., Protocatechuic Acid Promoted Alachlor Degradation in Fe(III)/H2O2 Fenton System. Environ. Sci. Technol. 2015, 49, 18


Page 18 of 30

Page 19 of 30


(13), 7948. 11. Song, W.; Cheng, M.; Ma, J.; Ma, W.; Chuncheng Chen, A.; Zhao, J., Decomposition of Hydrogen Peroxide Driven by Photochemical Cycling of Iron Species in Clay. Environ. Sci. Technol. 2006, 40, (15), 4782-4787. 12. Lyu, L.; Zhang, L.; Wang, Q.; Nie, Y.; Hu, C., Enhanced Fenton Catalytic Efficiency of γ-Cu-Al₂O₃ by σ-Cu²⁺-Ligand Complexes from Aromatic Pollutant Degradation. Environ. Sci. Technol. 2015, 49, (14), 8639-8647. 13. Sorokin, A.; De Suzzoni-Dezard, S.; Poullain, D.; Noël, J.-P.; Meunier, B., CO2 as the ultimate degradation product in the H2O2 oxidation of 2, 4, 6-trichlorophenol catalyzed by iron tetrasulfophthalocyanine. J. Am. Chem. Soc. 1996, 118, (31), 7410-7411. 14. Gupta, S. S.; Stadler, M.; Noser, C. A.; Ghosh, A.; Steinhoff, B.; Lenoir, D.; Horwitz, C. P.; Schramm, K. W.; Collins, T. J., Rapid total destruction of chlorophenols by activated hydrogen peroxide. Science (New York, N.Y.) 2002, 296, (5566), 326-328. 15. Aguiar, A.; Ferraz, A., Fe3+- and Cu2+-reduction by phenol derivatives associated with Azure B degradation in Fenton-like reactions. Chemosphere 2007, 66, (5), 947-54. 16. Canals, M.; Gonzalez-Olmos, R.; Costas, M.; Company, A., Robust iron coordination complexes with N-based neutral ligands as efficient fenton-like catalysts at neutral pH. Environ. Sci. Technol. 2013, 47, (17), 9918-9927. 17. Piera, J.; Backvall, J. E., Catalytic oxidation of organic substrates by molecular 19



oxygen and hydrogen peroxide by multistep electron transfer - A biomimetic approach. Angew. Chem. Int. Edit. 2008, 47, (19), 3506-3523. 18. Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, (6028), 443-447. 19. Ferrandon, M.; Kropf, A. J.; Myers, D. J.; Artyushkova, K.; Kramm, U.; Bogdanoff, P.; Wu, G.; Johnston, C. M.; Zelenay, P., Multitechnique Characterization of a Polyaniline-Iron-Carbon Oxygen Reduction Catalyst. J.phys.chem.c 2012, 116, (30), 16001-16013. 20. Jia, Q.; Ramaswamy, N.; Hafiz, H.; Tylus, U.; Strickland, K.; Wu, G.; Barbiellini, B.; Bansil, A.; Holby, E. F.; Zelenay, P., Experimental Observation of Redox-Induced Fe-N Switching Behavior as a Determinant Role for Oxygen Reduction Activity. Acs Nano 2015, 9, (12), 12496-12505. 21. Serov, A.; Artyushkova, K.; Atanassov, P., Fe-N-C Oxygen Reduction Fuel Cell Catalyst Derived from Carbendazim: Synthesis, Structure, and Reactivity. Adv. Energy Mater. 2014, 4, (10), 919-926. 22. Ma, J.; Yang, Q.; Wen, Y.; Liu, W., Fe-g-C3N4/graphitized mesoporous carbon composite as an effective Fenton-like catalyst in a wide pH range. Appl. Catal. B-environ. 2017, 201, 232-240. 23. Clarens, A. F.; Resurreccion, E. P.; White, M. A.; Colosi, L. M., Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks. Environ. Sci. Technol. 2010, 44, (5), 1813-1819. 20


Page 20 of 30

Page 21 of 30


24. Lau, P. S.; Tam, N. F. Y.; Wong, Y. S., Wastewater nutrients (N and P) removal by carrageenan and alginate immobilized Chlorella vulgaris. Environ. Technol. 1997, 18, (9), 945-951. 25. Xia, Y.; Xiao, Z.; Dou, X.; Huang, H.; Lu, X. H.; Yan, R. J.; Gan, Y. P.; Zhu, W. J.; Tu, J. P.; Zhang, W. K.; Tao, X. Y., Green and Facile Fabrication of Hollow Porous MnO/C Microspheres from Microalgaes for Lithium-Ion Batteries. Acs Nano 2013, 7, (8), 7083-7092. 26. Harris, P. O.; Ramelow, G. J., Binding of Metal-Ions by Particulate Biomass Derived from Chlorella-Vulgaris and Scenedesmus-Quadricauda. Environ. Sci. Technol. 1990, 24, (2), 220-228. 27. Bader, H.; Sturzenegger, V.; Hoigné, J., Photometric method for the determination of low concentrations of hydrogen peroxide by the peroxidase catalyzed oxidation of N,N-diethyl- p -phenylenediamine (DPD). Water Res. 1988, 22, (9), 1109-1115. 28. Bing, J.; Hu, C.; Nie, Y.; Yang, M.; Qu, J., Mechanism of Catalytic Ozonation in Fe2O3/Al2O3@SBA-15 Aqueous Suspension for Destruction of Ibuprofen. Environ. Sci. Technol. 2015, 49, (3), 1690-1697. 29. Neamtu, M.; Catrineseu, C.; Kettrup, A., Effect of dealumination of iron(III)-exchanged Y zeolites on oxidation of Reactive Yellow 84 azo dye in the presence of hydrogen peroxide. Appl. Catal. B-environ. 2004, 51, (3), 149-157. 30. Dhakshinamoorthy, A.; Navalon, S.; Alvaro, M.; Garcia, H., Metal Nanoparticles as Heterogeneous Fenton Catalysts. Chemsuschem 2012, 5, (1), 46-64. 31. Li, Y.; Liu, H.; Li, W. J.; Zhao, F. Y.; Ruan, W. J., A nanoscale Fe(II) 21



metal-organic framework with a bipyridinedicarboxylate ligand as a high performance heterogeneous Fenton catalyst. Rsc Advances 2016, 6, (8), 6756-6760. 32. Li, X.; Xin, L.; Xu, L.; Wen, Y.; Ma, J.; Wu, Z., Highly dispersed Pd/PdO/Fe2O3 nanoparticles in SBA-15 for Fenton-like processes: confinement and synergistic effects. Appl. Catal. B-environ. 2015, 165, 79-86. 33. Matuszak, Z.; Reszka, K. J.; Chignell, C. F., Reaction of Melatonin and Related Indoles With Hydroxyl Radicals: EPR and Spin Trapping Investigations. Free Radic. Biol. Med. 1997, 23, (3), 367-72. 34. Buda, F.; Ensing, B.; Gribnau, M. C. M.; Baerends, E. J., O2 evolution in the Fenton reaction. Chem-eur. J. 2003, 9, (14), 3436-3444. 35. Li, X. F.; Liu, W. P.; Ma, J. Q.; Wen, Y. Z.; Wu, Z. C., High catalytic activity of magnetic FeOx/NiOy/SBA-15: The role of Ni in the bimetallic oxides at the nanometer level. Appl. Catal. B-environ. 2015, 179, 239-248. 36. de Souza, W. F.; Guimaraes, I. R.; Oliveira, L. C. A.; Giroto, A. S.; Guerreiro, M. C.; Silva, C. L. T., Effect of Ni incorporation into goethite in the catalytic activity for the oxidation of nitrogen compounds in petroleum. Appl. Catal. A-gen. 2010, 381, (1-2), 36-41. 37. Bokare, A. D.; Chikate, R. C.; Rode, C. V.; Paknikar, K. M., Effect of surface chemistry of Fe-Ni nanoparticles on mechanistic pathways of azo dye degradation. Environ. Sci. Technol. 2007, 41, (21), 7437-7443. 38. Lim, H.; Lee, J.; Jin, S.; Kim, J.; Yoon, J.; Hyeon, T., Highly active heterogeneous Fenton catalyst using iron oxide nanoparticles immobilized in alumina 22


Page 22 of 30

Page 23 of 30


coated mesoporous silica. Chem. Commun. 2006, (4), 463-465. 39. Tsai, C. W.; Tu, M. H.; Chen, C. J.; Hung, T. F.; Liu, R. S.; Liu, W. R.; Lo, M. Y.; Peng, Y. M.; Zhang, L.; Zhang, J., Nitrogen-doped graphene nanosheet-supported non-precious iron nitride nanoparticles as an efficient electrocatalyst for oxygen reduction. Rsc Advances 2011, 1, (7), 1349-1357. 40. Lin S. S. and Gurol M. D., Catalytic Decomposition of Hydrogen Peroxide on Iron Oxide: Kinetics, Mechanism, and Implications. Environ. Sci. Technol. 1998, 32, (10), 1417-1423. 41. Lyu, L.; Zhang, L.; Hu, C., Galvanic-like cells produced by negative charge nonuniformity of lattice oxygen on d-TiCuAl-SiO2 nanospheres for enhancement of Fenton-catalytic efficiency. Environ. Sci. Nano 2016, 3, (6),1483-1492. 42. Yao, Y.; Fu, Q.; Zhang, Y. Y.; Weng, X.; Li, H.; Chen, M.; Jin, L.; Dong, A.; Mu, R.; Jiang, P., Graphene cover-promoted metal-catalyzed reactions. P. Natl. Acad. Sci. Usa. 2014, 111, (48), 17023. 43. Liu, S. Q.; Xiao, B.; Feng, L. R.; Zhou, S. S.; Chen, Z. G.; Liu, C. B.; Chen, F.; Wu, Z. Y.; Xu, N.; Oh, W. C., Graphene oxide enhances the Fenton-like photocatalytic activity of nickel ferrite for degradation of dyes under visible light irradiation. Carbon 2013, 64, (9), 197-206. 44. Yao, Y.; Mao, Y.; Zheng, B.; Huang, Z.; Lu, W.; Chen, W., Anchored Iron Ligands as an Efficient Fenton-Like Catalyst for Removal of Dye Pollutants at Neutral pH. Ind. Eng. Chem. Res. 2014, 53, (20), 8376–8384. 45. Georgi, A.; Schierz, A.; Trommler, U.; Horwitz, C. P.; Collins, T. J.; Kopinke, F. 23



D., Humic acid modified Fenton reagent for enhancement of the working pH range. Appl. Catal. B-environ 2007, 72, (1-2), 26-36. 46. Singh, K. P.; Bae, E. J.; Yu, J. S., Fe-P: A New Class of Electroactive Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137, (9), 3165-3168. 47. Park, J.; Yan, M. D., Covalent Functionalization of Graphene with Reactive Intermediates. Accounts. Chem. Res. 2013, 46, (1), 181-189.

24


Page 24 of 30

Page 25 of 30


Figure Captions Figure

1.

Catalyst

micrographs.

(a)

HAADF-STEM

image

of

Fe-N/Pentlandite-Al2O3/C; (b) Elements mapping of the chosen area by the yellow box; (c) SAXS 2D scattering patterns; (d)-(e) HRTEM images of the same particle. (f) Structure scheme of catalyst. Figure 2. (a) N 1s XPS spectra of the catalyst; (b) Fe L-edge XANES spectra of the catalyst and model compounds. Figure 3. Catalytic degradation of AR 73 and phenol by Fe-N/Pentlandite-Al2O3/C catalyst (Initial AR 73 concentration 50 mg/L; phenol concentration 30 mg/L; pH 6.8; T=25 ºC, catalyst dosage 0.4 g/L; H2O2 concentration 40 mM). Figure 4. (a) The concentrations of Fe2+ on the catalysts surface in different degradation systems; (b) The concentrations of Fe2+ during catalytic degradation of AR 73 in addition to C2H5OH or Na2CO3. (Initial AR 73 concentration 50 mg/L; pH was adjusted to 6.8 using H2SO4 solution; T=25 ºC, catalyst dosage 0.4 g/L; H2O2 concentration 40 mM). Figure 5. Scheme of the possible mechanism for Fe-N/Pentlandite-Al2O3/C catalyst in the Fenton reaction.

25



Figure 1

26


Page 26 of 30

Page 27 of 30


(a)

Pyridonic N 398.5 eV

Fe-Nx

Intensity (a.u.)

400.5 eV

Oxidized N 403.9 eV

406

404

402

400

398

396

394

16

(b)

Fe2O3

L3

Pyrrolic Fe-N4(calcined)

FeS Normailization (arb.units)

Normalization (arb.units)

Binding Energy (eV)

12

8

Fe-N/Pentlandite-Al2O3/C

B

2.6

Fe-N/Pentlandite-Al2O3/C

2.5

A

2.4 2.3

CD

2.2 2.1 695

700

705

710

715

720

725

730

Energy (eV)

L2

4 700

705

710

715

720

Energy (eV) Figure 2

27


725


Page 28 of 30

Concentration C/C0

1.0 0.8 0.6 0.4 AR73 AR73+H2O2 phenol phenol+H2O2

0.2 0.0

0

5

10

15

20

Time (min) Figure 3

28


25

30


Concentration of Fe2+ (µmol/g)

Page 29 of 30

4 (a)

3

2 Catalyst+AR 73+H2O2 Catalyst+H2O2 Catalyst+AR 73

1

0 0

5

10

15

20

25

30

Time (min)

Concentration of Fe2+ (µmol/g)

0.25 (b)

0.20 0.15 0.10 0.05

With C2H5OH With Na2CO3

0.00

0

5

10

15

20

25

Time (min) Figure 4

29


30


Page 30 of 30

R• e−

Fe3+

R + HO•

Fe3+

H2O2 Fe2+

Fe2+

R organic substrate R• reactive organic radical

Figure 5

30


Pentlandite from Microalgae: High

Recommend Documents