Multifunctional C doped CoFe2O4 material as co-catalyst to promote

Subscriber access provided by UNIV OF DURHAM

Article

Multifunctional C doped CoFe2O4 material as co-catalyst to promote the ROSs generation over magnetic recyclable C-CoFe/Ag-AgX photocatalysts Shuquan Huang, Yuanguo Xu, Meng Xie, Yun Ma, Jia Yan, Yeping Li, Yan Zhao, Hui Xu, and Huaming Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b02279 • Publication Date (Web): 19 Jul 2018 Downloaded from http://pubs.acs.org on July 20, 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 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Multifunctional C doped CoFe2O4 material as co-catalyst to promote the ROSs generation over magnetic recyclable C-CoFe/Ag-AgX photocatalysts Shuquan Huang†, Yuanguo Xu*,†, Meng Xie‡, Yun Ma†, Jia Yan†, Yeping Li‡, Yan Zhao†, Hui Xu†, Huaming Li*,†. Shuquan Huang: † School of Chemistry and Chemical Engineering, Institute for Energy Research,

Jiangsu

University,

Zhenjiang

212013,

PR

China,

E-mail

address:

[email protected] Yuanguo Xu: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Meng Xie: ‡ School of Pharmacy, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Yun Ma: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Jia Yan: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Yeping Li: ‡ School of Pharmacy, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Yan Zhao: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Hui Xu: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] Huaming Li: † School of Chemistry and Chemical Engineering, Institute for Energy Research, Jiangsu University, Zhenjiang 212013, PR China, E-mail address: [email protected] *Corresponding

Author:

Yuanguo

Xu,

E-mail

address:

[email protected];

+86-511-88791108; Huaming Li, E-mail address: [email protected]; Tel: +86-511-88791108;

1

ACS Paragon Plus Environment

Tel:

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Photocatalytic water disinfection has been demonstrated as a promising technology for rapid water treatment in terms of utilizing sustainable solar energy. In this paper, C doped CoFe2O4 magnetic nanoparticles (named as C-CoFe) modified C-CoFe/Ag-AgX (X=Cl, Br, I) composites were synthesized via solvothermal process. The photocatalytic performance of the C-CoFe/Ag-AgX composites were evaluated by bacterial inactivation in aqueous solution under visible light irradiation, the results showed that the C-CoFe/Ag-AgX composites were able to inactivate E. coli with a low photocatalysts concentration. And, compare to pure Ag-AgX, the C-CoFe/Ag-AgX composites exhibited enhanced photocatalytic performance, in which the 5% C-CoFe/Ag-AgBr showed the most inactivate activities that can achieve rapid water disinfection with 7 log inactivation of E. coli within 40 min under visible light. With the analysis and discussion of photo-electrochemistry test, ESR trapping experiments, H2O2 yield measurement and O2 control photocurrent response text, it was demonstrated that C-CoFe can work as a co-catalyst component in the C-CoFe/Ag-AgX composite to extract the photogenerated electrons and offer more oxygen activation sites to yield more reactive oxygen species (ROSs) for the photocatalytic inactivation. More importantly, the as-prepared C-CoFe/Ag-AgX composite possess magnetic properties which can be recovered easily by a magnetic field. Key words: Magnetic photocatalysts; Ag-AgX; CoFe2O4; Photocatalytic antibacterial

Introduction 2


Page 2 of 31

Page 3 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Recently, using photocatalytic technology to meet the water purification with low energy consumption strategies has aroused wide considerations1. Up to now, a variety of semiconductor materials, such as TiO2

2-3

, g-C3N4

4-5

, BiOBr 6, Bi2WO6

7-8

, AgX

9-10

, Ag3VO4

11

and red

phosphorus 12etc., have been researched for photocatalytic water disinfection. However, despite the fact that great efforts have been made, photocatalysis water disinfection technologies are still restricted by various factors for practical applications. It is therefore necessary to design environmentally benign catalysts which possess specific features including high activity, good recyclability and stability 13. Silver/silver halides (Ag-AgX, X = Cl, Br, I) have been recognized as one of the most efficient antibacterial photocatalysts. Whilst Ag-AgX shows great potential in the antibacterial application, serious aggregation and photo-corrosion as well as the difficulties in recycling the nanoparticles hinder its large-scale application

14-17

. Numerous strategies have been attempted to solve these

problems. For example, compositing with other semiconductors to improving the stability and dispersity catalysts

18-19

20-22

; depositing Ag-AgX nanoparticles on exceptional structures to recycle the

; using magnetically recoverable nanoparticles to separate the photocatalysts from

solutions 13. Among them, magnetic separation of photocatalysts seems to be a rational strategy to fully utilize the advantages of nanoparticle photocatalysts

23

. Traditional magnetic

photocatalysts with a core-shell structure need a SiO2 shell to prevent photo-dissolution of Fe3O4/(γ-Fe2O3) and transfer electrons-holes from semiconductors to core particle. Such as Fe3O4@SiO2@AgCl:Ag

24

, γ-Fe2O3@SiO2@AgBr:Ag

25

, Ag–AgI/Fe3O4@SiO2

26

and so on.

However, most of the magnetic photocatalysts studies only take the magnetic particles as a magnetic carrier. Quite few studies investigated the synergistic effects between the magnetic 3



particles and semiconductors. Moreover, the report about bacterial inactivity by magnetic photocatalysts is rare 13. Recently, our group and other groups have prudently realized that the family of spinel ferrite such as MxFe3−xO4 (M = Cu, Co, Ni, Zn, Mn) not only exhibit remarkable mechanical hardness, excellent ferromagnetic behaviors, good chemical and light stabilities, but also emerging as a new class of highly efficient Pt-free catalyst for oxygen reduction reaction ORR. Among them, the MxFe3−xO4 plays an important role in the O−O bond activation/cleavage and oxide removal process27-30. Indeed, semiconductor materials are always slack in the O−O bond activation/cleavage and oxide removal process

31

. In other words, semiconductors are

nonspecific in catalyzing oxygen reduction reaction in the photocatalytic reactions. As a result, the production of ROSs which can serve as powerful oxidants to inactivate various microorganisms in photocatalytic processes is limited

12

. Hence, evenly distribution of

MxFe3−xO4 nanoparticles on the surface of Ag-AgX particles would work as a co-catalyst to offer more oxygen activation sites and yield more ROSs. In fact, Cui et al. have demonstrated that the introduction of oxygen active catalyst can effectively boost the ROSs yield toward rapid water disinfection recently 32. Furthermore, the coupling of magnetic nanoparticles and semiconductor nanoparticles can qualify the photocatalysts magnetic properties for easily recycling the photocatalysts. In this work, in order to enhance the electrical conductivity, we chose the C doped CoFe2O4 material reported by our previous work as the magnetic nanoparticles and prepared a core-shell structure liked C-CoFe/Ag-AgX (X = Cl, Br, I) magnetic photocatalysts via a simple solvothermal method successfully

33

. The incorporated C-CoFe nanoparticles could worked as 4


Page 4 of 31

Page 5 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


specific component to extract photo-excited electrons from Ag/AgX and active them with the adsorbed O2 to generate ROSs. With the photo-excited electrons extraction, the carrier recombination was inhibited. As a result, the obtained C-CoFe/Ag-AgX composites exhibited excellent photocatalytic disinfection towards the Escherichia coli (E. coli) bacteria, especially the 5% C-CoFe/Ag-AgBr composite, can achieve rapid water disinfection with 7 log inactivation of E. coli within 40 min under visible light. In addition, due to the outstanding magnetic properties of C-CoFe, the C-CoFe/Ag-AgX photocatalysts can be recycled easily. At last, the insight photocatalytic mechanisms were discussed in detail.

Experimental section All the reagents were purchased from Sinopharm Chemical Reagent Co., Ltd., which were analytical grade and used without further purification. Preparation of C-CoFe nanoparticles The C element doped CoFe2O4 material were prepared via a sol–gel method reported in our previous work 33-34. Fabrication of C-CoFe/Ag-AgX Typically, C-CoFe nanoparticles were completely dispersed in 30 mL ethylene glycol via ultrasonic treatment and then AgNO3 were added under vigorous mechanical stirring. After further stirring for 30 min, certain amounts of KX (X= Cl, Br, I) were added to the above solution and kept stirring for another 60 min. The reaction temperature was kept at 15°C by a water cycle system. Subsequently, the suspensions were transferred to Teflon-lined stainless-steel autoclaves and kept at 140°C for 20 h. After cooling to room temperature, the as-prepared 5



Page 6 of 31

photocatalysts were washed with deionized water and ethanol for three times, respectively. And then dried under 60°C overnight. The added contents of C-CoFe in the C-CoFe/Ag-AgX composites were adjusted by simply controlling the weight ratio of CoFe2O4 to AgNO3. The final products were named as x % C-CoFe/Ag-AgX (x is the weight ratio of CoFe2O4 to AgNO3). Detail material input mass and ratio is listed in Table S1. Characterizations and photocatalytic bacterial inactivation experiments This part is provided in supporting information. Results and discussion Characterization of the obtained samples The C-CoFe was prepared by calcining the citric acid sol–gel of Co2+ and Fe3+ ions. To incorporate the C elements into the C-CoFe, the calcination temperature was kept at 300°C

33

.

C-CoFe/Ag-AgX composites were realized by a solvothermal method using the as-prepared C-CoFe NPs. As shown in Figure 1, the typical XRD pattern of C-CoFe is matched well with the crystal planes of the spinel-type CoFe2O4 (JCPDS card no. 22-1086). The incorporated C elements in the C-CoFe were determined by EDS-mapping analysis (Figure S1), in which the homogeneously distribution of Co, Fe, O and C elements were clearly observed. These results indicate that the C-CoFe material was successfully synthesized. As for these Ag-AgX, the XRD patterns can be well indexed to the cubic phase AgCl (JCPDS card no. 31-1238), cubic phase AgBr (JCPDS card no. 06-0438) and hexagonal AgI phase (JCPDS card no. 09-0374), respectively. The profiles of the C-CoFe/Ag-AgX composites patterns are nearly identical to those of pure Ag-AgX, respectively. Indicating the introduction of C-CoFe NPs has not been incorporated into the lattice of AgX or affected the crystallinity of AgX. Meanwhile, the peaks of 6


Page 7 of 31

C-CoFe and Ag0 are ambiguously observed in the C-CoFe/Ag-AgX composite materials, which should be ascribed to the lower content and high dispersion of Ag0 and C-CoFe species on these nanocomposites. l C g A g A / e F o C C l C g A / g A r B g A g A / e F o C C r B g A / g A

)

. u . a

(

y t i s n e t n I

I g A g A / e F o C C I g A g A e F o C C 0 8

0 7

0 6

0 5

2

0 4

0 3

0 2

0 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


θ/°

Figure 1 XRD patterns of the as-prepared C-CoFe, Ag-AgX and each 5% C-CoFe/Ag-AgX composites. The high-resolution XPS spectra were carried out to reveal the Ag0 and C-CoFe species in the C-CoFe/Ag-AgX composites. Figure 2a shows the high-resolution Ag 3d XPS spectra of Ag-AgX, it can be seen that two peaks of Ag species can be divided in each AgX materials. The first half bands around 367.5 and 373.5 eV are attributed to the Ag+ state, and latter half bands are ascribed to the metallic Ag0 state. These results confirm that the reduction of AgX to Ag0 solvothermal with EG solution

14, 35

. Note that, obvious shifts have been observed in the XPS

peaks of Ag species, which is because the binding energy will shift to a lower chemical state due to the enrichment of electrons on the surface. In contrast, higher chemical state shift can be 7



attributed to the electron-deficient on the surface 36. Therefore, as shown in Figure S5, after the electron enriched C-CoFe materials coupled with the Ag-AgX, the peaks of Ag in XPS of Ag-AgCl and Ag-AgBr will shift to lower chemical state while higher chemical state shift will happen in Ag-AgI due to the atomic radius of Cl and Br is smaller than that of I. The high-resolution XPS spectra of Co 2p displays two characteristic peaks corresponding to the Co2+ 2p3/2 and Co2+ 2p1/2 spin–orbit split peaks, respectively, with a satellite peak for Co2+28 (Figure 2b). For the XPS spectra of Fe 2p (Figure 2c), the binding energies of Fe3+ 2p3/2, Fe3+ 2p1/2 and Fe3+ satellite are observed. The XPS results of Co 2p and Fe 2p confirmed the existence of CoFe2O4 in the C-CoFe/Ag-AgX composites. l C g A g A / e F o C C

d 3 g A

(a)

C/s

r B g A g A / e F o C C I g A g A / e F o C C

364

366

368 370 372 374 Binding Energy (eV)

376

378

l C g A g A / e F o C C

p 2 o C

r B g A g A / e F o C C

(b)

I g A g A / e F o C C

+

2 /

p3 2

2 o C

+

e t i l l e t a s

2 o C

+

2 /

p1 2

2 o C

s / C

)

8


0 1 8

V e

(

0 0 8

y g 0 r 9 e 7 n E g n i d n i 0 8 B 7

0 7 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 31

Page 9 of 31

l C g A g A / e F o C C r B g A g A / e F o C C

p 2 e F

(c)

I g A g A / e F 2 / o p1 C 2 C + 3 e F e t i l l e t a s + 3 2 e / p3 F 2

+

3 e F

s / C

0 4 7

V e

(

0 3 7

y g 0r 2e 7n E g n i d n i 0 1B 7

0 0 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


)

Figure 2 High-resolution XPS spectra the 5% C-CoFe/Ag-AgX composites. (a) Ag 3d; (b) Co 2p; (c) Fe 2p. Microstructures of the as-prepared samples were observed by SEM and TEM measurements. The typical SEM images of Ag-AgX and 5% C-CoFe/Ag-AgX composites are displayed in Figure 3. As can be seen, the pure Ag-AgX are irregular particles whose possess smooth surface and large size (Figure 3a-c). The 5% C-CoFe/Ag-AgX composites also show irregular particles morphologies without any big changes compared to the pure Ag-AgX (Figure 3d-f). While the surfaces of the C-CoFe/Ag-AgX composites became rough and some holes can be observed, indicating the introduction of C-CoFe was the main reason affected the surface of Ag-AgX in the synthesis process. And the enlargement of the selected area (Figure 3g-i) indicated that the C-CoFe was evenly attached to the surface of Ag-AgX. Figure 4a displayed a typical TEM image of 5% C-CoFe/Ag-AgBr which could be clearly seen that the C-CoFe nanoparticles were on the surface of Ag-AgBr. High-resolution transmission electron microscopy images of 5% C-CoFe/Ag-AgBr is shown in Figure 4b, revealing the presence of AgBr, Ag, CoFe2O4 and C. The fringe spacing of 0.27 nm, 0.24 nm and 0.48 nm corresponding to the (200), (111) and (111) plane of the AgBr, Ag and CoFe2O4, respectively. The evenly distribution of C-CoFe NPs were further confirmed by the EDS-mapping. As shown in Figure S2-S4. the C, Co, Fe, O, Ag and X 9



elements were homogeneously distributed within the C-CoFe/Ag-AgX composites particles. We could not detect C element in the EDS-mapping analysis, mainly due to the low content in the composites. All these results have provided a strong evidence for the formation of core-shell structure liked C-CoFe/Ag-AgX hybrid material.

Figure 3 SEM images of the as-prepared samples: (a) Ag-AgCl; (b) Ag-AgBr; (c) Ag-AgI; (d) 5% C-CoFe/Ag-AgCl; (e) 5% C-CoFe/Ag-AgBr; (f) 5% C-CoFe/Ag-AgI; (g) enlargement of the selected area in (d); (h) enlargement of the selected area in (e); (i) enlargement of the selected area in (f).

Figure 4 TEM and HRTEM images of the typical 5% C-CoFe/Ag-AgBr composite: (a) a HRTEM of the surface; (b) an enlarged HRTEM image. 10


Page 10 of 31

Page 11 of 31

The magnetism of the photocatalyst have been investigated. As shown in Figure 5, the hysteresis loops of C-CoFe and these 5% C-CoFe/Ag-AgX composites display characteristic ferrimagnetic features. Their saturation magnetization (Ms), remnant magnetization (Mr) and coercivity (Hc) are listed in Table 1. It can be seen that the C-CoFe possess excellent magnetic abilities with Ms of 29.4 emu/g, Mr of 2.31 emu/g and Hc of 199.7 Oe. For these 5% C-CoFe/Ag-AgX composites, the Ms have been reduced greatly, but the Hc are all around 199.6 Oe without any considerable difference (inset Figure 5). The reduced Ms in these 5% C-CoFe/Ag-AgX can be attributed to the nonmagnetic Ag-AgX increased the total mass of the composites particles. While the no changed Hc indicates that these composites have inherited the magnetism of C-CoFe

37-40

. Figure S6 displays the digital photos of 5% C-CoFe/Ag-AgX

composites separated from water under an external magnetic field. 0 3 I g A g A / e F o C C % 5 e F o C C

)

l C g A g A / e F o C C % 5 ) (

0 . 0

0 2 -

4 . 0 8 . 0 -

0 0 0 0 2

)

0 0 0 2

0 0 0e 1O

(

0 0 0 0 1e O

(

d l e i 0F c i t e 0n 0g 0a 1M -

d l e i 0f c i t e n 0g 0a 0M 0 1 -

0 0 0 0 2 03 -

0 0 0 2 -

n o i t a z i t e n g a M

4 . 0

0 1 -

g / u m e

8 . 0

(

0

n o i t a z i t e n g a M

0 1

g / u m e

r B g A g A / e F o C C % 5

0 2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


)

Figure 5 The hysteresis loops of the as-prepared samples. Table 1 The parameters of the hysteresis loops. Sample

Ms (emu/g)

Mr (emu/g)

Hc (Oe)

C-CoFe 5% C-CoFe/Ag-AgCl 5% C-CoFe/Ag-AgBr 5% C-CoFe/Ag-AgI

29.4 1.98 1.54 0.61

2.31 0.19 0.15 0.06

199.7 199.6 199.6 199.6

11



The optical properties of pure Ag-AgX and typical C-CoFe/Ag-AgX composites were studied via DRS technology. The results are shown in Figure 6, it can be seen that the entire pure Ag-AgX exhibit the typical absorption patterns of semiconductors, which have clear absorption band edges. The corresponding absorption band edges are at 400 nm, 460 nm and 450 nm over AgCl, AgBr and AgI, respectively. The introduction of C-CoFe had undoubtedly heightened the absorbance of prepared composites in the whole region (200 nm ≤ λ ≤ 800 nm), respectively. Note that, although the C-CoFe was favorable to absorb visible light, the enhanced optical energy may not be used to drive the photogeneration of electrons and holes (detailed mechanism study will be introduced in the electrochemistry measurement section) 41. In addition, the surface plasmon resonance (SPR) absorption peak of each C-CoFe/Ag-AgX also can be observed, indicating the existence of metallic Ag nanoparticles. The Eg values calculated from UV-vis DRS of Ag-AgX were shown in the respective inserts. From the results, Eg values of 3.1 eV, 2.6 eV and 2.8 eV should pertain to AgCl, AgBr and AgI, respectively, the AgBr possesses the smallest band gap. The optical property of C-CoFe also has been conducted, as shown in Figure 6d, it can be seen the strong and consecutive absorption in the whole range, corresponding with its narrow band gap of 0.8 eV.

( α) ν

V e 6 . 2

4

( α) ν

8

0 . 1

5 . 3

0 . 3

5 . 2

0 . 02

8 . 0

h

5 . 3

ν (eV)

6 . 0

h

0V . 3e

5 . 2

0 . 02

0 . 1

)

r B g A

r B g A g A 2

h

V e 1 . 3

5

2 . 1

( ν

4 . 0

8 . 0

e c n a b r o s b A

2 1


0 1

4 . 1 e c n a b r o s b A

h

2 . 1

2

4 . 1

5 1

l C g A / g A

(b)

l C g A

e F o C C @ g A / g A % 5

6 . 1

(a)

6 . 1

8 . 1

2 . 0

6 . 0

0 0 8


)

0 0 7

12

(

n

h t g n e l e

)

0 0 6m

0 0 5

0v 0a 4W

0 0 3

0 0 02 . 0

0 0 8

0 0 7

(

0 0 6 m n

h 0 t 0 g 5 n e l e 0 v 0 a 4 W

0 0 3

0 0 42 . 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 31

0 . 3

8 . 2

6 . 2

0

2

2

(αhν)

e F o C C

V e 8 . 2

4

40

0

2 3 hν (eV)

4

5

0 0 8

0 0 7

n

(

1

0 0 6m

e l e

h 0t 0g 5n

0v 0a 4W

0 0 3

0 0 8

0 0 7

)

V e 8 . 0

20 0

n

0 0 6m

e l e

h 0t 0g 5n

0v 0a 4W

0 0 3

(

e F o C C

8

hν (eV)

e c n a b r o s b A

0 0 2 9 8 7 6 5 4 3 2 1 0 0 . . . . . . . . . . . 2 1 1 1 1 1 1 1 1 1 1

I g A

2 1

(d)

I g A g A

e c n a b r o s b A

I g A g A / e F o C C % 5

(c)

0 0 2 6 . 4 2 0 8 6 4 2 0 . . . . . . . . 1 1 1 1 0 0 0 0 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(αhν)

Page 13 of 31

)

Figure 6 UV-vis/DRS spectra of the as-prepared samples: (a) Ag-AgCl and 5% C-CoFe/Ag-AgCl; (b) Ag-AgBr and 5% C-CoFe/Ag-AgBr; (c) Ag-AgI and 5% C-CoFe/Ag-AgI; The respective inserts figures were the Eg values calculated from UV-vis DRS plot. Photocatalytic disinfection activities Figure 7 displays the disinfection performance of the as-prepared photocatalysts. The dark control experiments of the as-prepared samples were first carried out (Figure 7a-c). From the results, it can be concluded that: (1) at low concentration, the Ag-AgX displayed little toxic effect to E. coli. in dark control; (2) the Ag-AgX and C-CoFe/Ag-AgX composites exhibited low toxic effect at the concentration of 50 ug/mL without light irradiation. (3) the toxic effect order over the Ag-AgX and C-CoFe/Ag-AgX composites is Cl > Br > I, which can be attributed to the Ksp of AgX are Cl > Br > I. Figure 7d-f show the results of photocatalytic disinfection activities, as can be seen, the light alone had no bactericidal effect, and C-CoFe alone still showed no disinfection activities to the bacterial cells in visible light. Meanwhile, Ag-AgX and C-CoFe/Ag-AgX composites exhibited good disinfection activities under visible light irradiation, the photocatalytic disinfection performances were enhanced after the C-CoFe NPs introduced. Interestingly, all of the optimum photocatalyst of each C-CoFe/Ag-AgX composites systems is 5% C-CoFe/Ag-AgX. It seems that the C-CoFe component part may work as a co-catalyst just like 13



Pt in the g-C3N4 hydrogen evolution systems

41-44

Page 14 of 31

. The most active photocatalyst is the 5%

C-CoFe/Ag-AgBr, which can reach 107 cfu/mL of E. coli inactivation within 40 min, while 5% C-CoFe/Ag-AgCl and 5% C-CoFe/Ag-AgI would spend 60 min and 80 min, respectively, to reach the level at the same condition (Figure 7g). This is an identical tendency to the previous reported Ag/AgX-rGO system

9-10, 45

. For the optimal 5% C-CoFe/Ag-AgBr composite, another

two typical harmful bacterial: Staphylococcus aureus (S. aureus) and Canidia albicans (C.

albicans) also have been used as model substance to evaluate the photocatalytic disinfection activities. As shown in Figure S7, about 3 log S. aureus could be inactivated by 5% C-CoFe/Ag-AgBr composite under visible light irradiation for 120 min. While for the C.

albicans, no obvious cell density decreasing can be observed. Indicating the as-prepared C-CoFe/Ag-AgX composite possess selectivity to the different harmful bacterial. Although, the optimum 5% C-CoFe/Ag-AgBr is still not as efficient as the biosynthesized Ag nanoparticles, as which can obtain total inactivation of 106 cfu/mL E. coli K-12 within 1 min, the present photocatalysts process the advantages of easy to synthesize and recycle Figure S6. Since the 5% C-CoFe/Ag-AgBr exhibited the highest photocatalytic performance in C-CoFe/Ag-AgX, thus Ag-AgBr and C-CoFe/Ag-AgBr with different weight ratios were chosen to search for the optimum one. Figure 7h displays the stability and recyclability of 5% C-CoFe/Ag-AgBr. The results evidenced that the photocatalytic activity of 5% C-CoFe/Ag-AgBr did not decline significantly after five cycles of E. coli inactivation under visible light irradiation, indicating its good reusability and promising industrialization in water purification. In many cases, Ag+ ions released from Ag-based photocatalysts need to be considered due to its bactericidal activities at a concentration high than 0.5 µg/mL 14


9-10, 30

. Therefore, the

Page 15 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


concentration of Ag+ ions in the photocatalysis process of multicycle experiment were also studied. As shown in Figure S8a, the Ag+ concentration is gradually increased in the first run, it could finally reach 0.4925 µg/mL which is close to the critical Ag+ concentration (0.5 µg/mL). While in the multicycle experiments, the concentration of Ag+ is not high. It is 0.3186, 0.2912, 0.2075 and 0.1742 µg/mL in the end of Cycle 1, Cycle 2, Cycle 3 and Cycle 4, respectively. In order to exclude the effects by Ag+ in the photocatalytic disinfection process, the bactericidal abilities of released Ag+ ions at the concentration of 0.17, 0.2, 0.25, 0.3, and 0.49 µg/mL under visible light irradiation were also evaluated. As shown in Figure S8b, little effects to the cell density can be observed when the concentration of Ag+ is less than 0.3 µg/mL, but it become obvious at the concentration of 0.4925 µg/mL which is reached only at the end of the first run. These results indicated that the released Ag+ from the composite may not play a serious bactericidal effect in present study and the efficient inactivation of bacterial mainly come from the sustainable generated reactive species of visible light irradiated 5% C-CoFe/Ag-AgBr. Furthermore, it is important to check the amount of heavy metal ions Co2+ release in water treatments by Co content composites 46, the amount of Co2+ ions released from the composite in subsequent cycle of multicycle experiment have been checked. As shown in Figure S8a, even after reaction for 200 min, the Co2+ ions in this photocatalytic process are at very low level (about 0.0053 µg/mL), lower than the detection limits of the atomic absorption spectrophotometer (ContrAA 300, Analytikjena, Germany), suggesting the Co2+ ions were hard to release from the composites. In order to reveal the prominent species in the photocatalytic inactivation process, a series of reactive

species

trapping

experiments

were

15


conducted.

Catalase,


4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy (TEMPOL), Cr(VI), oxalate, and isopropanol used •−

here were for the H2O2, O2 , photo-excited electrons, photo-excited holes and •OH, respectively 32

. In order to obtain the highest but non-toxic to the bacterium concentration of each scavenger,

a screening of all scavenge was performed. As shown in Figure S9, the optimum concentration of catalase, Cr(VI), 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy (TEMPOL), isopropanol and oxalate are 0.4 mg/mL, 0.4 mM, 0.02 mM, 0.4 mM and 0.1 mM, respectively. From the result showed in Figure 7i, it was found that among these scavengers, catalase has the strongest effect. Then was the isopropanol, Cr(VI) and TEMPOL. Oxalate showed little effect to the photocatalytic disinfection efficiency. In addition, in consideration of the •Br radical is a strong bacterial inactivation species, •Br radical in the photocatalytic process have been tested by using Electron Spin Resonance (ESR) spin-trap of DMPO-•Br and Mass Spectrometry (MS) of DMPO-Br. As shown in Figure S10, there was no ESR or MS signal of •Br radical could be found, indicating the •Br radical cannot be formed by the 5% C-CoFe/Ag-AgBr composite in the photocatalytic process. These results confirmed that the excellent bactericidal effect of photocatalysts mainly come from the sustainable generated ROSs.

l o r t n o c t h g i L e F o C C I g A g A

)

) (

) (

(

) (

0 8

0 7

0 6

0 5i n m 0 4 e m 0i 3T

)

I g A g A / e F o

(

I g A g A / e F o

I g A g A / e F o

)

I g A g A

I g A g A / e F o C C % 0 1 I g A g A / e F o C C % 5

0

0 4

0 3

40 ( )

n i m

20

e m i T

n i m

r B 0 g 2e A m i g T A / e F o C 0 C 1 % 5

0

0



1

r B g A g A / e F o C C % 0 1

0

n i


2

r B g A g A

1

0 8

0 6

m l C 0 g 4e A m i g T A / e F o C 0 C 2 % 5

16

3

e F o C C

2

l C g A g A / e F o C C % 3

0

)

4

l o r t n o c t h g i L

3

l C g A g A / e F o C C % 0 1

0

(

5

4

l C g A g A

1

y t i s n e d l l e C

6

5

L m / u f c g l

)

7

(f)

6

e F o C C

2

(

l o r t n o c k r a D

e F o C C C C C C - - 0 C C 2 % 0 % % 1 3 5 0 1

0

0 4

0 3

n i

(

)

7

l o r t n o c t h g i L


8 7 6 5 4 3 2 1 0


n i m

e m i T

m r B 0 g 2e A m g i A T / e F o C 0 C 1 % 5

0

0 8

0 6

0 4

0 2

3

)



4 (

r B g A g A / e F o C C % 0 1


5

L m / u f c g l


r B g A g A

l C g A g A / e F o C C % 0 1

(e)

6


(

)

7

L m / u f c g l

(c) L m / u f c g l

e F o C C

l C g A g A

0

(

(d)

L m / u f c g l y t i s n e d l l e C

e F o C C



L m / u f c g l

(b)

8 7 6 5 4 3 2 1 0

(a)

8 7 6 5 4 3 2 1 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 31

60

80

)

)

) (

I V r C

(

l o n a o r p o s I ( )

L O P M E T e t a l a x O

0 4

(

0 3

n i m 0 2e m i

r T e g n e v 0 a 1 c s o N

)

0

0 0 2

0 6 1

0 2n 1i m

e m 0i 8T

0 4

0

0 8

0 6

n i m 0 4e m i T

0 2

0

(

e s a l a t a C

0


4 3 2 1 0

L m / u f c g l

6 5

(i)

7

h

t 5

h

d

t 4

r 3

d

1 )

n 2

2 (

t


3


s 1


4


L m / u f c g l

5

L m / u f c g l

7 6 5 4 3 2 1 0

(h)


6

(g)

7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(

Page 17 of 31

)

Figure 7 Disinfection performance: (a, b, c) Inactivation of E. coli by the as-prepared samples in dark condition; (d, e, f) Inactivation of E. coli by the as-prepared samples in visible light irradiation; (g) comparison photocatalytic disinfection activities of 5% C-CoFe/Ag-AgX composites; (h) photocatalytic inactivation of E. coli by 5% C-CoFe/Ag-AgBr composite in different repeated cycles. (i) Photocatalytic disinfection performance with respective ROSs scavengers (Catalase, 0.4 mg/mL; isopropanol, 0.4 mM; Cr(VI), 0.02 mM; TEMPOL, 0.4 mM; sodium oxalate, 0.1 mM) in the presence of 5% C-CoFe/Ag-AgBr composite. To better understand the destruction progress of bacteria in the photocatalysis process, the morphology and microstructure of E. coli at different time intervals were examined by SEM study. Before testing, an equal amount of bacteria solution was extracted at the time of 0, 10, 20, 30, 40 and 80 min in the photocatalytic disinfection process and fixed on a silicon pellet with 2.5% glutaraldehyde solution at 4°C for 12h. Subsequently, the silicon pellet was sequentially dehydrated with 30, 50, 70, 90, and 100% ethanol for 30 min, respectively. The SEM test results are shown in Figure 8, at the time of 0 min, the E.coil bacterial shows a well preserved plump rod shape with rough membranes. After photocatalytic treatment for 10 min, the cell has collapsed and shows transparent smooth cell membranes. When the treatment come to 20 min, the cell membranes have been broken and sinking in the middle part of the cell could be observed, which indicating the leakage of cytoplasm. Further treatment to 30 min, perforation have been found on the cell. Aggravating shrink and rupture can be found at the time of 40 min. 17



These SEM images indicated that photocatalytic treatment of the as-prepared samples induced the oxidative damage to the cell membrane. Furthermore, when prolonged the photocatalytic reaction time to 80 min, the leaked bacterial cell debris have been crumpled together, which can be found in other bacterial inactivation reports. In whole SEM shooting process, photocatalysts were not observed contact with the bacterial, again confirm that E. coli were mainly killed by the generated ROSs in the photocatalysis process7.

Figure 8 SEM images of E. coli during the photocatalysis treatment with 5% C-CoFe/Ag-AgBr composite under visible light irradiation for 0, 10, 20, 30, 40 and 80 min. Photocatalytic enhancement mechanisms propose As aforementioned, compared to pristine Ag-AgBr, the C-CoFe/Ag-AgBr composites exhibited enhanced photocatalytic bactericidal disinfection performance. To gain insight into the mechanisms on enhancing the photocatalytic activity of Ag-AgBr, photo-electrochemistry measurements over the pure Ag-AgBr and C-CoFe/Ag-AgBr composites were performed. From Figure 9a, it can be seen that C-CoFe almost had no photocurrent responses and Ag-AgBr displays a typical semiconductor responses ability with steady on-off cycles. Surprisingly, the photocurrent responses were enhanced after Ag-AgBr coupling with C-CoFe, which display a 18


Page 18 of 31

Page 19 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hump-like photocurrent response depending on the loading amount of C-CoFe (with 5% as an optimal amount). This phenomenon can be reasonably explained as that the C-CoFe worked like a co-catalyst component in the C-CoFe/Ag-AgBr composites 47. Therefore, increment of C-CoFe loading will improve the charge separation efficiency but also shield the light absorption of semiconductor host, and thus, it should appear an optimal balance between these two contradictory factors at a certain loading amount of C-CoFe (5%). Furthermore, the electrochemical impedance spectroscopy (EIS) test also implied this hypothesis, as shown in Figure 9b, the arc radiuses of C-CoFe/Ag-AgBr are smaller than that of pure Ag-AgBr but show little differences between these composites. It is worth noting that the C-CoFe possesses a small arc radius, indicating its low resistivity. Combine with the photocurrent test results, it can be inferred that the photogenerated electron transfer from Ag-AgBr to C-CoFe upon irradiation thus favored effective charge separation. In order to provide proof for this, Mott-Schottky plots of pure Ag-AgBr and C-CoFe/Ag-AgBr film electrodes were showed in Figure 9c-d. The flat potentials of Ag-AgBr and C-CoFe were calculated to be - 0.21 and -0.82 V versus the Ag/AgCl electrode, respectively. Indicating the Ag-AgBr possesses a much higher donor density than C-CoFe. In addition, the carrier density of Ag-AgBr is about three times that of C-CoFe as shown in the slope of the Mott-Schottky plots48. In summary, the results of electrochemistry tests indicating that the C-CoFe could extract the photogenerated electrons on the CB of Ag-AgBr thus improve the separation and transfer of photogenerated charge carriers, which is one of the key roles in response for the superior photocatalytic activities of C-CoFe/Ag-AgBr composites.

19



0 6 r B g A g A / e F o C C % 5 r B g A g A / e F o C C % 0 1

0 2

-Z'' (Ohm)

e F o C C

0 4

e F o C C

2 . 1

r B g A g A

)


r B g A g A / e F o C C % 0 1

( µ

r B g A g A


(b)

8 . 0

6 . 1 4 . 0 0 . 0

t n e r r u c o t o h P


2

m c / A

0 . 2

(a)

4 . 2

(

)

) (

V 2 8 . 0 -

(

z H 0 0 0 1

V 1 2 . 0 -

1 0 . 0

5 . 0

0 . 0

5 . 0 -

0 . 1 -

0 . 1

l C g A / g A . s V V l a i t n e t o P

l 5C . 0g A / g A . s V 0 .V 0 l a i t n e t o 5P . 0 -

5 . 1 0. 0

0 0 . 0 (

z H 0 0 5 1

2 . 0

2 0 . 0

2 -

C

4 . 0

2

F 0 1 0 1

3 0 . 0

C

e F o C C

z H 0 5 2 1

4 0 . 0

2 -

6 . 0

z H 0 0 5 1

5 0 . 0

2

F 0 1 0 1

)

8 . 0

(d)

r B g A g A

6 0 . 0

(c)

0 0 2

0 5m 1h O ' Z -

s

0 0 1

0

0 8 2

0 6 2

0 4 2

0 2 e 2 m i T

0 0 2

0 8 1

( )

7 0 . 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 31

)

(

)

Figure 9 Electrochemistry measurements: (a) Photocurrent responses of C-CoFe, Ag-AgBr and C-CoFe/Ag-AgBr composites; (b) electrochemical impedance spectroscopy plot of C-CoFe, Ag-AgBr and C-CoFe/Ag-AgBr composites; (c) Mott-Schottky plots of Ag-AgBr; (d) Mott-Schottky plots of C-CoFe. Another indispensable step of photocatalysis is the surface/interface catalytic reaction, in which the separated charges reacted with adsorbed O2 and H2O separately to form ROSs here. In present study, the generation of ROSs likely to be the direct contributions to the photocatalytic disinfection activities as resulted from the trapping experiments and bacteria SEM analysis. Therefore, the ROS generation over Ag-AgBr and 5% C-CoFe/Ag-AgBr composite were studied. Figure 10a-b display the electron spin resonance (ESR) spin-trap of DMPO- •OH and DMPO-

O2•−, respectively. As observed, both Ag-AgBr and 5% C-CoFe/Ag-AgBr composite show no signals in dark. When turn on the light, the ESR signals of DMPO- •OH and DMPO- O2•− could 20


Page 21 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


be detected both on Ag-AgBr and 5% C-CoFe/Ag-AgBr composite. Compared with the pure Ag-AgBr, the ESR signal intensity were enhanced over the 5% C-CoFe/Ag-AgBr composite, •−

suggesting the •OH and O2 generation abilities of Ag-AgBr under visible light irradiation have been improved after C-CoFe decorating. Figure 10c is the H2O2 yields of C-CoFe, Ag-AgBr and 5% C-CoFe/Ag-AgBr, which shows that the H2O2 formation has been improved after no H2O2 produce property C-CoFe nanoparticle was loaded on Ag-AgBr. Combine with the results of electrochemistry tests, it indicates that migration of photogenerated electron to the loaded co-catalyst and reduction of surface-adsorbed O2 followed by H2O2 and O2

•−

formation on the

C-CoFe surface have to proceed smoothly. To validate the aforementioned C-CoFe could act as a co-catalyst to provide more active sites for ROSs generation. A serious of O2 control experiments were carried out. Firstly, we compared the photocatalytic disinfection activity of 5% C-CoFe/Ag-AgBr composite with and without O2. The results are shown in Figure 10d, without O2, the disinfection activity was greatly inhibited, which confirmed that the sustainable generated ROSs from the reduction of O2 were responsible for the rapid photocatalytic disinfection activity. Secondly, an O2 control photocurrents experiments was designed to reveal the active sites of ROSs generation (Detail experiment processes were conducted in supporting information.). Since the carrier transfer habit can be directly reflected by the photocurrent response signals, in fact, there would be a compaction between the working electrodes and the dissolved O2 in the photogenerated carriers’ transfer process. When the electrochemistry tests condition was O2 free (N2 pretreated condition), major of the photogenerated carriers would transfer to the ITO working electrodes and exhibited a high photocurrent response ability. Correspondingly, part of the photo-generated carriers would react 21



with the O2 instead of transfer to the ITO electrode if the O2 was contained in the electrochemistry tests. Therefore, the decrease rate of photocurrent response in a same working electrode caused by replacing N2 with O2 would reflect the O2 reduction reaction abilities and the active sites of a semiconductor. Figure 10e-f display the results of O2 control photocurrents experiments over pure Ag-AgBr and 5% C-CoFe/Ag-AgBr composite. It can be clearly seen that the photocurrents intensities were immediately decreased in all samples. While the decrease rate of pure Ag-AgBr and 5% C-CoFe/Ag-AgBr composite was 20% and 50%, respectively, which implies that the photo-excited electrons in 5% C-CoFe/Ag-AgBr composite were more apt to react with the adsorbed O2 than pure Ag-AgBr. In addition, 5% wt. C-CoFe/TiO2 was synthesized to further exclude the photo-excited carriers contribution come from the C-CoFe. The 5% wt. C-CoFe/TiO2 composite barely displayed photocatalytic disinfection activity even after 4 h visible light irradiation (Figure S12). Considering that the nano-size effect, size distribution histogram with Gaussian-fitting curve of the as-prepared samples have been conducted. As shown in Figure S13-15, the diameters of particles have been decreased with the increasing of C-CoFe content in these composites. They have been from 3.26 µm, 4.03 µm and 4.27 µm to 1.94 µm, 1.68 µm and 1.13 µm for the Ag-AgCl, Ag-AgBr and Ag-AgI, respectively. The decreased particle size may be increasing the active sits and therefore improve the photocatalytic activities. However, the photocatalytic bactericidal performance has been reduced obviously when the content of C-CoFe was increased to 10% which lead to the smallest particle size in the as-prepared samples. Indicating that the nano-size effect of the as-prepared samples also may not the main contribution to the superior photocatalytic disinfection activities. These experiments result strongly suggest the introduced C-CoFe materials could act as a co-catalyst to 22


Page 22 of 31

Page 23 of 31

extract photogenerated electrons and provide active sites for ROSs generation. Dark

Ag-AgBr

Visible light

(b)

)

. u . a

Ag-AgBr

Intensity (a.u.)

(a)

5% C-CoFe/Ag-AgBr

Dark

(

y t i s n e t n I

Visible light

2

) (

3

µ

4 N n i r B g A g A / e F o C C % 5

1

5

r 2i A n i r B g A g A / e F o C C % 5

0

0

0 4

0 . 3

(

0 3

n i m 0 2e m i T

0 1

0

0 0 1

0 8

0n 6i m

e m 0i 4T

0 2

0

)

N n i r B g A g A / e F o C C % 5 O n i r B g A g A / e F o C C % 5 2

2

2 . 1

O n i r B g A g A

5 . 2

2

2

N n i r B g A g A

4 . 1 8 . 0

( µ)

5 . 1

% 0 5


0 . 1

A

0 . 2

% 0 2

0 . 1

( µ)

318.4

5

0 1

(f)

318.2 )

T m

d l e i F (

6

5 1 )

318.0

7

e F o C C

0 2


A

6 . 0

5 . 0


Dark

8 2 3

6 2 3

4 2 3T m

2l d 2e 3i F

0 2 3 r B g A g A

L m / u f c g l

(

(e)

Visible light

Visible light

(d)


5 2 2

O 2 H

Ag-AgBr

317.8

)

0 3

L / l o m

Dark

5% C-CoFe/Ag-AgBr

(

(c)

Ag-AgBr

5% C-CoFe/Ag-AgBr

5% C-CoFe/Ag-AgBr

8 1 3 4 . 0

0 . 0 0 8 2

0 6 2

0 4 2s

e 0m 2i 2T

0 0 2

0 8 1

0 4 2

0 2 2

0 0 2 s

e 0 m 8 i 1 T

0 6 1

0 4 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


( )

( )

Figure 10 Reactive oxygen species measurement: (a) ESR spectra of DMPO-•OH in the •−

presence of Ag-AgBr and 5% C-CoFe/Ag-AgBr composite; (b) ESR spectra of DMPO- O2 in the presence of Ag-AgBr and 5% C-CoFe/Ag-AgBr composite; (c) Comparison of the H2O2 production on Ag-AgBr and 5% C-CoFe/Ag-AgBr composite. (d) Photocatalytic disinfection activity of 5% C-CoFe/Ag-AgBr composite with and without O2. (e) Photocurrent responses of Ag-AgBr in O2 contained and free electrolyte; (f) Photocurrent responses of 5% 23



C-CoFe/Ag-AgBr composite in O2 contained and free electrolyte. According to all above-mentioned results and discussions, a possible photocatalytic mechanism of enhancing ROSs formation over C-CoFe/Ag-AgBr composite was proposed, as shown in Figure 11, the Ag-AgBr possesses a much higher carrier donor density compare to C-CoFe and that could enable the C-CoFe acting as electron acceptors to transfer the electrons and thus hindering the recombination of electron-hole pairs. Under visible light irradiation, the host semiconductor Ag-AgBr system was excited to generate SPR hot electrons, photogenerated electrons and holes. The hot electrons and photogenerated electrons could react with the •−

dissolved oxygen to form H2O2 and O2 . However, the photogenerated electrons and holes •−

would quickly recombined, thus only bits of O2 and •OH can be formed and participated in the photocatalysis process. After the co-catalysts like C-CoFe materials was decorated on the Ag-AgBr, both of the hot and photogenerated electrons can be extracted by the C-CoFe and the C-CoFe work as activity sites for the H2O2 and O2

•−

generation, thus inhibited the carriers’

recombination and enough holes were accumulated to generated •OH. Therefore, promote the photocatalytic activities.

Figure 11 Proposed mechanism of ROSs generation in pure Ag-AgX and C-CoFe co-catalyst modified C-CoFe/Ag-AgX composites. 24


Page 24 of 31

Page 25 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Conclusions

In conclusion, we have demonstrated the magnetic recyclable photocatalysts for rapid water disinfection with an easy closed material, C-CoFe/Ag-AgX composites. By decorating C-CoFe nanoparticles on the surface of Ag-AgX to work as a co-catalyst for photogenerated electrons extraction and offering active sites to boost the ROSs yield. This not only improve the photocatalytic antibacterial activities, but also enable the C-CoFe/Ag-AgX composites to magnetic recyclable. The optimum photocatalyst 5% C-CoFe/Ag-AgBr composite showed a rapid inactivation of 107 cfu/mL bacteria in only 40 min at a low photocatalysts concentration (50 µg/mL) and good recyclability with no significant decline after five cycles. The promising performance of C-CoFe/Ag-AgX composites on bacteria shows great potential as photocatalysts for the rapid visible-light inactivation of bacteria in water. The concept demonstrated here mainly highlights that the surface decoration of oxygen activation magnetic nanoparticles, such as MxFe3−xO4 (M = Fe, Cu, Co, Mn), can be a wonderful strategy to construct versatile magnetic photocatalysts with wide applications. Supporting Information Characterizations section, Photocatalytic bacterial inactivation experiments, Electrochemical measurements, EDS-mapping, Screening of the scavenges, Size distribution histogram with Gaussian-fitting curve of the as-prepared samples, magnetic separation digital photos and Ag+, Co2+ ions concentration test and some other experiments dates. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (No. 21777063, 21506079, 21407065), the Natural Science Foundation of Jiangsu Province 25



(BK20140533), the China Postdoctoral Science Foundation (2015T80514, 2017M621654) and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX18_2266).

Reference (1) Loeb, S.; Hofmann, R.; Kim, J.-H. Beyond the Pipeline: Assessing the Efficiency Limits of Advanced Technologies for Solar Water Disinfection. Environ. Sci. Tech. Let. 2016, 3 (3), 73-80, DOI: 10.1021/acs.estlett.6b00023. (2) Nie, X.; Li, G.; Gao, M.; Sun, H.; Liu, X.; Zhao, H.; Wong, P.-K.; An, T. Comparative Study On the Photoelectrocatalytic Inactivation of Escherichia coli K-12 and Its Mutant Escherichia coli BW25113 Using TiO2 Nanotubes as A Photoanode. Appl. Catal. B: Environ. 2014, 147, 562– 570, DOI: 10.1016/j.apcatb.2013.09.037. (3) Kochkina, N. E.; Agafonov, A. V.; Vinogradov, A. V.; Karasev, N. S.; Ovchinnikov, N. L.; Butman, M. F. Photocatalytic Activity of Biomorphic TiO2 Fibers Obtained by Ultrasound-Assisted Impregnation of Cellulose with Titanium Polyhydroxocomplexes. ACS Sustain. Chem. Eng. 2017, 5 (6), 5148-5155, DOI: 10.1021/acssuschemeng.7b00504. (4) Wang, W.; Yu, J. C.; Xia, D.; Wong, P. K.; Li, Y. Graphene and g-C3N4 Nanosheets Cowrapped Elemental Alpha-sulfur as A Novel Metal-Free Heterojunction Photocatalyst for Bacterial Inactivation Under Visible-Light. Environ. Sci. Technol. 2013, 47 (15), 8724-8732, DOI: 10.1021/es4013504. (5) Sun, L.; Du, T.; Hu, C.; Chen, J.; Lu, J.; Lu, Z.; Han, H. Antibacterial Activity of Graphene Oxide/g-C3N4 Composite Through Photocatalytic Disinfection Under Visible Light. ACS Sustain. Chem. Eng. 2017, 5 (10), 8693-8701, DOI: 10.1021/acssuschemeng.7b01431. (6) Wu, D.; Yue, S.; Wang, W.; An, T.; Li, G.; Yip, H. Y.; Zhao, H.; Wong, P. K. Boron Doped BiOBr Nanosheets with Enhanced Photocatalytic Inactivation of Escherichia coli. Appl. Catal. B: Environ. 2016, 192, 35-45, DOI: 10.1016/j.apcatb.2016.03.046. (7) Jia, Y.; Zhan, S.; Ma, S.; Zhou, Q. Fabrication of TiO2-Bi2WO6 Binanosheet for Enhanced Solar Photocatalytic Disinfection of E. coli: Insights on the Mechanism. ACS Appl. Mater. Inter. 2016, 8 (11), 6841-6851, DOI: 10.1021/acsami.6b00004. (8) Zhu, X.; Liu, J.; Zhao, Z.; Yan, J.; Xu, Y.; Song, Y.; Ji, H.; Xu, H.; Li, H. Hydrothermal Synthesis of mpg-C3N4 and Bi2WO6 Nest-Like Structure Nanohybrids with Enhanced Visible Light Photocatalytic Activities. RSC Adv. 2017, 7 (61), 38682-38690, DOI: 10.1039/c7ra06681c. (9) Shi, H.; Li, G.; Sun, H.; An, T.; Zhao, H.; Wong, P.-K. Visible-Light-Driven Photocatalytic Inactivation of E. coli by Ag/AgX-CNTs (X=Cl, Br, I) Plasmonic Photocatalysts: Bacterial Performance and Deactivation Mechanism. Appl. Catal. B: Environ. 2014, 158-159, 301-307, DOI: 10.1016/j.apcatb.2014.04.033. (10) Xia, D.; An, T.; Li, G.; Wang, W.; Zhao, H.; Wong, P. K. Synergistic Photocatalytic Inactivation Mechanisms of Bacteria by Graphene Sheets Grafted Plasmonic Ag/AgX (X = Cl, Br, I) Composite 26


Page 26 of 31

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Photocatalyst

under

Visible

Light

Irradiation.

Water

Res.

2016,

99,

149-161,

DOI:

10.1016/j.watres.2016.04.055. (11) Jing, L.; Xu, Y.; Huang, S.; Xie, M.; He, M.; Xu, H.; Li, H.; Zhang, Q. Novel Magnetic CoFe2O4/Ag/Ag3VO4 Composites: Highly efficient Visible Light Photocatalytic and Antibacterial Activity. Appl. Catal. B: Environ. 2016, 199, 11–22, DOI: 10.1016/j.apcatb.2016.05.049. (12) Xia, D.; Shen, Z.; Huang, G.; Wang, W.; Yu, J. C.; Wong, P. K. Red Phosphorus: An Earth-Abundant Elemental Photocatalyst for “Green” Bacterial Inactivation under Visible Light. Environ. Sci. Technol. 2015, 49 (10), 6264-6273, DOI: 10.1021/acs.est.5b00531. (13) Ng, T. W.; Zhang, L.; Liu, J.; Huang, G.; Wang, W.; Wong, P. K. Visible-Light-Driven Photocatalytic Inactivation of Escherichia coli by Magnetic Fe2O3-AgBr. Water Res. 2016, 90, 111-118, DOI: 10.1016/j.watres.2015.12.022. (14) Huang, S.; Xu, Y.; Chen, Z.; Xie, M.; Xu, H.; He, M.; Li, H.; Zhang, Q. A Core–Shell Structured Magnetic Ag/AgBr@Fe2O3 Composite with Enhanced Photocatalytic Activity for Organic Pollutant Degradation and Antibacterium. RSC Adv. 2015, 5 (87), 71035-71045, DOI: 10.1039/c5ra13403j. (15) Huang, S.; Xu, Y.; Xie, M.; Liu, Q.; Xu, H.; Zhao, Y.; He, M.; Li, H. A Z-Scheme Magnetic Recyclable Ag/AgBr@CoFe2O4 Photocatalyst with Enhanced Photocatalytic Performance for Pollutant and Bacterial Elimination. RSC Adv. 2017, 7 (49), 30845-30854, DOI: 10.1039/c7ra03936k. (16) Li, X.; Chen, D.; Li, N.; Xu, Q.; Li, H.; He, J.; Lu, J. AgBr-Loaded Hollow Porous Carbon Nitride with Ultrahigh Activity as Visible Light Photocatalysts for Water Remediation. Appl. Catal. B: Environ. 2018, 229, 155-162, DOI: 10.1016/j.apcatb.2018.02.028. (17) Yu, H.; Xu, L.; Wang, P.; Wang, X.; Yu, J. Enhanced Photoinduced Stability and Photocatalytic Activity of AgBr Photocatalyst by Surface Modification of Fe(III) Cocatalyst. Appl. Catal. B: Environ. 2014, 144, 75-82, DOI: 10.1016/j.apcatb.2013.06.023. (18) Ong, W.-J.; Putri, L. K.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T. Heterostructured AgX/g-C3N4 (X = Cl and Br) Nanocomposites via A Sonication-assisted Deposition-precipitation Approach: Emerging Role of Halide ions in The Synergistic Photocatalytic Reduction of Carbon Dioxide. Appl. Catal. B: Environ. 2016, 180, 530-543, DOI: 10.1016/j.apcatb.2015.06.053. (19) Sun, L.; Wu, W.; Tian, Q.; Lei, M.; Liu, J.; Xiao, X.; Zheng, X.; Ren, F.; Jiang, C. In situ Oxidation and Self-Assembly Synthesis of Dumbbell-Like α-Fe2O3/Ag/AgX (X = Cl, Br, I) Heterostructures with Enhanced Photocatalytic Properties. ACS Sustain. Chem. Eng. 2015, 4 (3), 1521-1530, DOI: 10.1021/acssuschemeng.5b01473. (20) Fan, Y.; Ma, W.; Han, D.; Gan, S.; Dong, X.; Niu, L. Convenient Recycling of 3D AgX/graphene Aerogels (X = Br, Cl) for Efficient Photocatalytic Degradation of Water Pollutants. Adv. Mater. 2015, 27 (25), 3767-3773, DOI: 10.1002/adma.201500391. (21) Zhao, H.; Zhang, L.; Gu, X.; Li, S.; Li, B.; Wang, H.; Yang, J.; Liu, J. Fe2O3–AgBr Nonwoven Cloth with Hierarchical Nanostructures as Efficient and Easily Recyclable Macroscale Photocatalysts. RSC Adv. 2015, 5 (15), 10951-10959, DOI: 10.1039/c4ra13254h. (22) Manna, J.; Goswami, S.; Shilpa, N.; Sahu, N.; Rana, R. K. Biomimetic Method to Assemble Nanostructured Ag@ZnO on Cotton Fabrics: Application as Self-Cleaning Flexible Materials with Visible-Light Photocatalysis and Antibacterial Activities. ACS Appl. Mater. Inter. 2015, 7 (15), 8076-8082, DOI: 10.1021/acsami.5b00633. (23) Wang, D.; Astruc, D. Fast-Growing Field of Magnetically Recyclable Nanocatalysts. Chem. Rev. 2014, 114 (14), 6949-6985, DOI: 10.1021/cr500134h. (24) An, C.; Ming, X.; Wang, J.; Wang, S. Construction of Magnetic Visible-Light-Driven Plasmonic 27



Page 28 of 31

Fe3O4@SiO2@AgCl : Ag Nanophotocatalyst. J. Mater. Chem. 2012, 22 (11), 5171-5176, DOI: 10.1039/c2jm16622d. (25) Tian, B.; Wang, T.; Dong, R.; Bao, S.; Yang, F.; Zhang, J. Core–Shell Structured γ-Fe2O3@SiO2@AgBr:Ag Composite with High Magnetic Separation Efficiency and Excellent Visible Light Activity for Acid Orange 7 Degradation. Appl. Catal. B: Environ. 2014, 147, 22-28, DOI: 10.1016/j.apcatb.2013.08.028. (26) Guo, J.-F.; Ma, B.; Yin, A.; Fan, K.; Dai, W.-L. Photodegradation of Rhodamine B and 4-Chlorophenol Using Plasmonic Photocatalyst of Ag–AgI/Fe3O4@SiO2 Magnetic Nanoparticle Under Visible Light Irradiation. Appl. Catal. B: Environ. 2011, 101 (3-4), 580-586, DOI: 10.1016/j.apcatb.2010.10.032. (27) Zhu, H.; Zhang, S.; Huang, Y. X.; Wu, L.; Sun, S. Monodisperse M(x)Fe(3-x)O4 (M = Fe, Cu, Co, Mn) Nanoparticles and Their Electrocatalysis for Oxygen Reduction Reaction. Nano. Lett. 2013, 13 (6), 2947-2951, DOI: 10.1021/nl401325u. (28) Lu, L.; Hao, Q.; Lei, W.; Xia, X.; Liu, P.; Sun, D.; Wang, X.; Yang, X. Well-Combined Magnetically Separable Hybrid Cobalt Ferrite/Nitrogen-Doped Graphene as Efficient Catalyst with Superior Performance for Oxygen Reduction Reaction. Small 2015, 11 (43), 5833-5843, DOI: 10.1002/smll.201502322. (29) Xu, Y.; Bian, W.; Wu, J.; Tian, J.-H.; Yang, R. Preparation and Electrocatalytic Activity of 3D Hierarchical Porous Spinel CoFe2O4 Hollow Nanospheres as Efficient Catalyst for Oxygen Reduction Reaction and Oxygen Evolution Reaction. Electrochim. Acta 2015, 151, 276-283, DOI: 10.1016/j.electacta.2014.11.042. (30) Huang, S.; Xu, Y.; Liu, Q.; Zhou, T.; Zhao, Y.; Jing, L.; Xu, H.; Li, H. Enhancing Reactive Oxygen Species Generation and Photocatalytic Performance via Adding Oxygen Reduction Reaction Catalysts into The Photocatalysts. Appl. Catal. B: Environ. 2017, 218, 174-185, DOI: 10.1016/j.apcatb.2017.06.030. (31) Wu, L.; Mendoza-Garcia, A.; Li, Q.; Sun, S. Organic Phase Syntheses of Magnetic Nanoparticles and

Their

Applications.

Chem.

Rev.

2016,

116

(18),

10473-10512,

DOI:

10.1021/acs.chemrev.5b00687. (32) Liu, C.; Kong, D.; Hsu, P. C.; Yuan, H.; Lee, H. W.; Liu, Y.; Wang, H.; Wang, S.; Yan, K.; Lin, D.; Maraccini, P. A.; Parker, K. M.; Boehm, A. B.; Cui, Y. Rapid Water Disinfection Using Vertically Aligned MoS2 Nanofilms and Visible Light. Nat. Nanotechnol. 2016, 11 (12), 1098-1104, DOI: 10.1038/nnano.2016.138. (33) Zhao, Y.; Xu, Y.; Zeng, J.; Kong, B.; Geng, X.; Li, D.; Gao, X.; Liang, K.; Xu, L.; Lian, J.; Huang, S.; Qiu, J.; Huang, Y.; Li, H. Low-Crystalline Mesoporous CoFe2O4/C Composite with Oxygen Vacancies for High Energy Density Asymmetric Supercapacitors. RSC Adv. 2017, 7 (87), 55513-55522, DOI: 10.1039/c7ra11741h. (34) Huang, S.; Xu, Y.; Xie, M.; Xu, H.; He, M.; Xia, J.; Huang, L.; Li, H. Synthesis of Magnetic CoFe2O4/g-C3N4 Composite and Its Enhancement of Photocatalytic Ability Under Visible-Light. Colloids Surf. A: Physicochem. Eng. Aspects 2015, 478, 71-80, DOI: 10.1016/j.colsurfa.2015.03.035. (35) Xu, Y.; Xu, H.; Yan, J.; Li, H.; Huang, L.; Zhang, Q.; Huang, C.; Wan, H. A Novel Visible-Light-Response Plasmonic Photocatalyst CNT/Ag/AgBr and Its Photocatalytic Properties. Phys. Chem. Chem. Phys. 2013, 15, 5821-5830, DOI: 10.1039/c3cp44104k. (36) Yu, Y.; Nam, G. H.; He, Q.; Wu, X. J.; Zhang, K.; Yang, Z.; Chen, J.; Ma, Q.; Zhao, M.; Liu, Z.; Ran, F. R.; Wang, X.; Li, H.; Huang, X.; Li, B.; Xiong, Q.; Zhang, Q.; Liu, Z.; Gu, L.; Du, Y.; Huang, 28


Page 29 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


W.; Zhang, H. High phase-purity 1T'-MoS2- and 1T'-MoSe2-layered crystals. Nature Chemistry 2018, 10 (6), 638-643, DOI: 10.1038/s41557-018-0035-6. (37) Wang, T.; Jiang, Z.; An, T.; Li, G.; Zhao, H.; Wong, P. K. Enhanced Visible-Light-Driven Photocatalytic Bacterial Inactivation by Ultrathin Carbon-Coated Magnetic Cobalt Ferrite Nanoparticles. Environ. Sci. Technol. 2018, 52 (8), 4774-4784, DOI: 10.1021/acs.est.7b06537. (38) Xia, D.; Ng, T. W.; An, T.; Li, G.; Li, Y.; Yip, H. Y.; Zhao, H.; Lu, A.; Wong, P. K. A recyclable mineral catalyst for visible-light-driven photocatalytic inactivation of bacteria: natural magnetic sphalerite. Environ. Sci. Technol. 2013, 47 (19), 11166-73, DOI: 10.1021/es402170b. (39) Wang, W.; Li, G.; Xia, D.; An, T.; Zhao, H.; Wong, P. K. Photocatalytic nanomaterials for solar-driven bacterial inactivation: recent progress and challenges. Environmental Science: Nano 2017, 4 (4), 782-799, DOI: 10.1039/c7en00063d. (40) Xia, D.; Li, Y.; Huang, G.; Yin, R.; An, T.; Li, G.; Zhao, H.; Lu, A.; Wong, P. K. Activation of persulfates by natural magnetic pyrrhotite for water disinfection: Efficiency, mechanisms, and stability. Water Res. 2017, 112, 236-247, DOI: 10.1016/j.watres.2017.01.052. (41) Yi, J.; She, X.; Song, Y.; Mao, M.; Xia, K.; Xu, Y.; Mo, Z.; Wu, J.; Xu, H.; Li, H. Solvothermal Synthesis of Metallic 1T-WS2 : A Supporting Co-catalyst on Carbon Nitride Nanosheets Toward Photocatalytic

Hydrogen

Evolution.

Chem.

Eng.

J.

2018,

335,

282-289,

DOI:

10.1016/j.cej.2017.10.125. (42) Zhang, G.; Li, G.; Lan, Z. A.; Lin, L.; Savateev, A.; Heil, T.; Zafeiratos, S.; Wang, X.; Antonietti, M. Optimizing Optical Absorption, Exciton Dissociation, and Charge Transfer of A Polymeric Carbon Nitride with Ultrahigh Solar Hydrogen Production Activity. Angew. Chem. Int. Ed. 2017, 56 (43), 13445-13449, DOI: 10.1002/anie.201706870. (43) She, X.; Wu, J.; Zhong, J.; Xu, H.; Yang, Y.; Vajtai, R.; Lou, J.; Liu, Y.; Du, D.; Li, H.; Ajayan, P. M. Oxygenated Monolayer Carbon Nitride for Excellent Photocatalytic Hydrogen Evolution and External Quantum Efficiency. Nano Energy 2016, 27, 138-146, DOI: 10.1016/j.nanoen.2016.06.042. (44) She, X.; Wu, J.; Xu, H.; Zhong, J.; Wang, Y.; Song, Y.; Nie, K.; Liu, Y.; Yang, Y.; Rodrigues, M.-T. F.; Vajtai, R.; Lou, J.; Du, D.; Li, H.; Ajayan, P. M. High Efficiency Photocatalytic Water Splitting Using 2D α-Fe2O3/g-C3N4 Z-Scheme Catalysts. Adv. Energy Mater. 2017, 7 (17), 1700025, DOI: 10.1002/aenm.201700025. (45) Shi, H.; Chen, J.; Li, G.; Nie, X.; Zhao, H.; Wong, P. K.; An, T. Synthesis and characterization of novel plasmonic Ag/AgX-CNTs (X = Cl, Br, I) nanocomposite photocatalysts and synergetic degradation of organic pollutant under visible light. ACS Appl. Mater. Inter. 2013, 5 (15), 6959-67, DOI: 10.1021/am401459c. (46) Vink, J. P. M.; van Zomeren, A.; Dijkstra, J. J.; Comans, R. N. J. When soils become sediments: Large-scale storage of soils in sandpits and lakes and the impact of reduction kinetics on heavy metals and

arsenic

release

to

groundwater.

Environ

Pollut

2017,

227,

146-156,

DOI:

10.1016/j.envpol.2017.04.016. (47) Qin, Y.; Li, G.; Gao, Y.; Zhang, L.; Ok, Y. S.; An, T. Persistent free radicals in carbon-based materials on transformation of refractory organic contaminants (ROCs) in water: A critical review. Water Res. 2018, 137, 130-143, DOI: 10.1016/j.watres.2018.03.012. (48) Park, H. S.; Kweon, K. E.; Ye, H.; Paek, E.; Hwang, G. S.; Bard, A. J. Factors in The Metal Doping of BiVO4 for Improved Photoelectrocatalytic Activity as Studied by Scanning Electrochemical Microscopy and First-Principles Density-Functional Calculation. J. Phys. Chem. C 2011, 115 (36), 17870-17879, DOI: 10.1021/jp204492r. 29



30


Page 30 of 31

Page 31 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphic Abstract

Synopsis The magnetic C-CoFe can act as a co-catalyst for photogenerated electrons extraction and offering active sites to boost ROSs yield.

31


Multifunctional C doped CoFe2O4 material as co-catalyst to promote

Recommend Documents