Pentlandite from Microalgae: High

Feb 12, 2018 - MOE Key Laboratory of Environmental Remediation & Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University...
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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

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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)

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Table of Contents Art

calcination

Fe, Al, Ni aniline polymerizing Chlorella vulgaris

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ABSTRACT

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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.

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

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INTRODUCTION

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

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

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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.

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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

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dramatically enhanced by the complexation of transition metal ions with

40

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

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

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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

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

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

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efficiency.17

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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MATERIALS AND METHODS

68

Chemicals

and

Reagents.

FeCl3·6H2O,

Al(NO3)3·9H2O,

Ni(NO3)2·6H2O,

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

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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

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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

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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

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

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

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

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

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

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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

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

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

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14.0, 9.86 and 34.9 mg/g, respectively.

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

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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

115

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

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

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

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stability and reusability.

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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

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

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

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

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

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

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spectrophotometric method28. Cyclic Voltammetry Measurements were performed

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

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

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RESULTS AND DISCUSSION

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

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

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

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

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

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

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

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distributed in the image.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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the characteristic peaks of Ni2+ ion and Al2O3 phase.

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

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different

metal

ions

as

shown

in

Figure

S4.

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

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

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

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

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

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

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

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

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

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

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can

be

seen

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

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

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

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

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

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

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organic compounds with more than 2 aromatic rings and indigent biodegradation

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

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

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

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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

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

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

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

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

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

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

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

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

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

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this novel Fenton system. 11

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

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

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

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

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

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

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

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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

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

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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.

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

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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

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

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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.

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

216

stability.

Good

catalytic

performance

and

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deactivation

of

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Synergistic

effects

of

metal

ions.

Compared

with

control

samples,

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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

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

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

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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.

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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

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

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

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

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

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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.

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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.

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

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

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

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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

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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.

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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

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

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

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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

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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

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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

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

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(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

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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

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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

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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.

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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.

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Figure 1

26

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(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

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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

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Concentration of Fe2+ (µmol/g)

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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

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R• e−

Fe3+

R + HO•

Fe3+

H2O2 Fe2+

Fe2+

R organic substrate R• reactive organic radical

Figure 5

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