Ag3PO4 Photocatalysts for Highly Efficient Degradation of Bisphenol A under Visible-light Irradiation

Journal Pre-proofs Novel Biochar@CoFe2O4/Ag3PO4 Photocatalysts for Highly Efficient Degradation of Bisphenol A under Visible-light Irradiation Yali Zhai, Youzhi Dai, Jing Guo, Lulu Zhou, Minxing Chen, Hantong Yang, Liangping Peng PII: DOI: Reference:

S0021-9797(19)30966-X https://doi.org/10.1016/j.jcis.2019.08.065 YJCIS 25321

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

31 May 2019 15 August 2019 16 August 2019

Please cite this article as: Y. Zhai, Y. Dai, J. Guo, L. Zhou, M. Chen, H. Yang, L. Peng, Novel Biochar@CoFe2O4/Ag3PO4 Photocatalysts for Highly Efficient Degradation of Bisphenol A under Visible-light Irradiation, Journal of Colloid and Interface Science (2019), doi: https://doi.org/10.1016/j.jcis.2019.08.065

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier Inc.

Novel Biochar@CoFe2O4/Ag3PO4 Photocatalysts for Highly Efficient Degradation of Bisphenol A under Visible-light Irradiation Yali Zhai, Youzhi Dai*, Jing Guo*, Lulu Zhou, Minxing Chen, Hantong Yang, Liangping Peng *

Department of Environmental Science and Engineering, College of Environment and Resources,

Xiangtan University, Xiangtan 411105, PR China

Graphical abstract

Abstract

In the study, a series of novel Z-scheme biochar@CoFe2O4/Ag3PO4 photocatalysts were synthesized and employed to degrade bisphenol A under visible light irradiation (λ≥420 nm). The structural morphology, optical properties and physicochemical properties of composites were characterized by means of TEM, XRD, FT-IR, XPS, UV-Vis, BET, EIS and VSM analysis. The photocatalytic performances of the photocatalysts were evaluated systematically. The MBA-3 photocatalyst exhibited the highest photocatalytic and mineralization ability within 60 min among all photocatalysts, 91.12% and 80.23%, respectively. After four cycles, the degradation of BPA *

Corresponding authors E-mail addresses: [email protected] (Youzhi Dai), [email protected] (Jing Guo).

still kept the photocatalytic activity of 73.94%, and the removal rate of TOC remained 58.96%. Moreover, the active species in the photocatalytic process were evaluated, and we proposed the Z-scheme photocatalytic mechanism for highly efficient degradation of BPA. According to the GC-MS results, the photodegradation pathway of BPA is also suggested. The present study has provided a valuable way of using the magnetic biochar in the design of new and efficient system for the degradation of organic pollutions in waste water.

Keywords Biochar@CoFe2O4/Ag3PO4;

Magnetic

biochar;

Magnetically

separable;

Visible

light

photocatalysis; Bisphenol A

1. Introduction

In recent years, bisphenol A (BPA), one of the most typical endocrine disrupting chemicals (EDCs), has been proven to be a huge threat to human health and the environment even at trace levels (less than 1 ng/L)[1]. BPA can be detected in most water environments, and its concentration considerably varies (from ng/L to µg/L)[2, 3]. According to recent research, long-term exposure to such environments not only affects thyroid hormone production and DNA transmission[4], but also causes dysplasia of the reproductive system[5] and a certain risk of carcinogenicity and teratogenicity[6, 7]. Therefore, highly efficient and stable methods are urgently needed to remove BPA from water environments. Silver (Ag)-based semiconductors have become increasingly popular for the degradation of organic pollution[8-13]. Generally, such semiconductors exhibit good photocatalytic activity by forming heterojunctions, thereby removing organic pollution well. Among these semiconductors, silver phosphate (Ag3PO4), a new type of visible light-responsive photocatalyst, shows higher quantum efficiency (90%) compared with other semiconductors and is favored for the construction of highly efficient photocatalysts[14]. However, Ag3PO4 has several drawbacks, thus considerably limiting its further application. One such drawback is photocorrosion caused by Ag+ reduction[15, 16]. Extensive effort has been exerted to solve this problem by constructing heterojunctions with

other semiconductors, such as Ag3PO4/BiOX[17-19], AgX/Ag3PO4[20], Ag3PO4/GO[21], Ag3PO4/WO3[22], Ag3PO4/TiO2[23, 24], which all improved photocatalytic performance better than unstructured heterojunctions. Meanwhile, the photocatalytic efficiency of the Z-scheme is much higher than other heterojunction photocatalysts[22]. Another vital issue that limits the practical application of Ag3PO4 is the desired recycling of photocatalysts. In this line, the introduction of magnetic materials is believed to be effective in material separation. Therefore, finding a semiconductor that can perform magnetic separation and form a heterostructure with Ag3PO4 is crucial. CoFe2O4, a narrow bandgap semiconductor, has excellent magnetic separation properties and good visible light responsiveness; it has been proven to form a heterojunction with Ag3PO4[25]. Biochar, a type of charcoal, has been receiving widespread attention because of its unique superiority over similar carbon materials. It has a large specific surface area that can provide more active sites for photocatalysis[26]. Zhou et al.[27] found that persistent free radicals (PFRs) in biochar can induce oxygen to produce ·O2-. Moreover, studies have shown that biochar can be used as a conduction medium for the Z-scheme system to promote a highly efficient separation of photogenerated electron holes[28, 29]. On this basis, this study proposes a novel Z-scheme mechanism visible-light photocatalyst based on biochar@CoFe2O4/Ag3PO4 composites. Biochar@CoFe2O4/Ag3PO4 is synthesized by in-situ precipitation. The structural morphology, optical properties, and physicochemical properties of the composites were characterized. In addition, the photocatalytic performance of the as-prepared materials and the active species in the photocatalytic process were systematically evaluated. Results demonstrate that the MBA-m composites exhibit higher photocatalytic activity compared with Ag3PO4. The Z-scheme photocatalytic mechanism and degradation intermediates are discussed in detail.

2. Experimental

2.1 Materials Pine pollen was purchased from Yunnan dekot biological engineering co. LTD. Cobalt nitrate

hexahydrate (Co(NO3)2·6H2O), iron nitrate hydrate (Fe(NO3)3·9H2O), silver nitrate (AgNO3) and sodium hydroxide (NaOH) were purchased from Xilong chemical co. LTD. Disodium hydrogen phosphate (Na2HPO4·12H2O), ethylene glycol (C2H6O2), ethylenediamine tetraacetic acid disodium (EDTA-2Na), isopropanol (IPA) and phenylhydrazine (BZQ) were purchased from Tianjin guangfu technology development co. LTD. The BPA used in the photocatalytic experiments was purchased from Aladdin reagent co. LTD. All the reagents used in the experiment except methanol (chromatographic grade) are of analytical grade and can be used without further purification.

2.2 Synthesis of the photocatalysts 2.2.1 Synthesis of biochar@CoFe2O4 (MB) The preparation of magnetic biochar was synthesized via a one-pot method. First, a certain amount of pine pollen was mixed in a mixture of Fe(NO3)3·9H2O (0.1 mol/L) and Co(NO3)2·6H2O (0.1 mol/L) and kept stirred overnight. Adjust pH=12 with NaOH (2 mol/L) and stir another 1 h. Transfer above solution into a Teflon-lined autoclave and keep heated at 180 ℃ for 12 h. Subsequently, the obtained powder was calcined at 500 ℃ for 2 h in a tube furnace at a rate of 5 ℃/min under an atmosphere of N2. Magnetic biochar (biochar@CoFe2O4) was finally obtained and denoted as MB.

2.2.2 Synthesis of biochar@CoFe2O4/Ag3PO4 (MBA) The facile in-situ precipitation method was used to synthesize biochar@CoFe2O4/Ag3PO4 with different ratios. In a typical process, a series of different qualities MB were added to 100 mL C2H6O2 and sonicated for 30 min. Afterwards, 50 mL AgNO3 (0.129 mol) was added and kept stirred for 12 h to make Ag+ combine with MB sufficiently. Subsequently, another 50 mL Na2HPO4·12H2O (0.043 mol) was added dropwise to the above mixed solution and then maintained with stirring for 1 h. The above mixture was washed several times with ultrapure water, and then collected for use. The synthesized biochar@CoFe2O4/Ag3PO4 with different ratios were denoted as MBA-m, and m represents the mass ratio of MB in the MBA-m composite. For example, MBA-1 means that the content of MB in the composite was 10wt%.

2.3 Characterization Transmission electron microscopy (TEM) image was observed by JEOL JEM2100 microscopy at an acceleration voltage of 200 kV. X-ray diffraction (XRD) patterns were analyzed by Rigaku D/max 2500 diffractometer equipped with Cu Kα radiation in the range of 10–90°. Fourier transform infrared spectroscopy (FT-IR) was used to investigate the bonding of surface elements of different materials. The chemical composition of the photocatalysts was analyzed by X-ray photoelectron spectroscopy (XPS). In order to study the optical absorption properties of the photocatalysts, the UV-vis spectroscopy were recorded on UV2550 spectrometer (Shimadzu) within the range of 200-800 nm. An adsorption instrument (TriStar II 3020, Micromeritics Company, USA) was used to evaluate the specific surface areas and pore structures of photocatalysts.

Electrochemical

impedance

spectroscopy

(EIS)

was

taken

by

760E

electrochemical workstation. The magnetic hysteresis loop was measured on a MPMS-XL-7 vibrating sample magnetometer.

2.4 Photocatalytic activity experiments The photocatalytic activities of MBA-m photocatalysts with BPA as target pollution were evaluated under visible-light irradiation. A 300 W Xe lamp (Xi'an Bilang Biotechnology Co. Ltd) furnished with a cutoff filter (λ≥420 nm) was used as a visible light source. In a typical process, adding a certain amount (25 mg) of catalyst to a quartz tube containing 50ml of BPA solution (20 mg/L). After the adsorption equilibrium was reached, and the lamp was turned on for photocatalytic reaction. Approximate 5 mL of the samples were withdrawn at given time intervals and treated with a 0.45 um water membrane. The concentrations of the BPA solution and TOC were quantified by HPLC (Agilent 1260) equipped with a UV–vis detector and TOC analyzer, respectively. The possible intermediates of BPA were analyzed by gas chromatography-mass spectrometry (GC-MS, Agilent 7890-5977B).

3. Results and discussion

3.1 TEM analysis

(a)

(c)

(d)

(f)

(g)

(i)

(j)

(b)

(e)

(h)

Fig. 1 (a)-(b) TEM images of MBA-3; (c) HAADF-STEM image; (d)-(i) EDX mapping of Ag, P, Co, Fe, O and C obtained from the MBA-3 composite; (j) EDX analysis of the MBA-3 composite

Fig. 1 shows the TEM and EDX mapping of MBA-3. It could be observed that CoFe2O4 and biochar were randomly loaded on the surface of the Ag3PO4, which indicated that heterojunctions have formed[30]. The HRTEM image of the MBA-3 photocatalyst shows the lattice spacing of 0.269 nm, 0.258 nm and 0.21 nm, which were corresponding to the (210) plane of Ag3PO4[31], (311) plane of CoFe2O4[32] and (101) plane of biochar[33], respectively (Fig. 1b). EDX mapping was performed to further verify that biochar, Ag3PO4 and CoFe2O4 was distributed in MBA-3 composite. As can be seen from Figs. 1c-i, the distribution of Ag, P, O, Fe, Co and C was relatively homogeneous in the surface of MBA-3, further confirming that heterojunctions has formed. In addition, EDX pattern of the MBA-3 was shown in Fig. 1j. Signals from Ag, P, and O are attributed to Ag3PO4, the signals for O, Fe and Co are from CoFe 2O4, and the signal of C is from biochar. This also gives strong evidence of the successful preparation of MBA-3 composite.

Intensity (a.u.)

3.2 XRD analysis

0

20

40

60

80

100

2-theta (degree)

Fig. 2 XRD pattern of as-prepared samples and biochar

Fig. 2 presents XRD patterns of individual Ag3PO4, MB and MBA-m, respectively. As we can see, in the diffraction pattern of the pure Ag3PO4, the position and relative intensity of all the diffraction peaks correspond to the standard card of cubic phase Ag3PO4 (JCPDS No. 06-0505)[34]. As for MB, it can be clearly seen that all the strong diffraction peak positions are consistent with the characteristic peak positions of the standard map of CoFe 2O4 (JCPDS No.22-1086)[35]. It should be noted that no significant characteristic diffraction peaks of biochar were observed in the map of MB and MBA-3 composite, which may be attributed to the

amorphous state[36] and the relatively small content of the biochar in the composites. For MBA-m samples, we found that their spectrum are similar to that of pure Ag3PO4, the co-existence of main peaks of Ag3PO4 and the weak characteristic peaks of MB represents co-existence of Ag3PO4 and MB. This also indicates that the introduction of MB had little effect on the crystal structure of Ag3PO4. The intensity of characteristic peaks of the photocatalysts varies with the change of loading ratio, but their position remains unchanged. In order to explore the effect of the biochar in MBA-3, the crystal size of samples were calculated from XRD patterns and shown in Table 1. According to the Scherrer equation[37], the crystal size of Ag3PO4, CoFe2O4 and MBA-3 are 61, 44 and 59.2 nm, respectively. Table 1 XRD data of as-prepared samples. Photocatalyst

Ag3PO4

CoFe2O4

MB

MBA-3

crystallite size (nm)

61.724

14.309

17.251

52.143

3.3 FT-IR analysis (a)

-CH2

Transmittance（ a.u.）

(b)

C-C

O-H

(c)

Co-O

(d)

P-O

Fe-O

O-H

4000

3600

3200

2800

2400

2000

-1

1600

1200

800

400

Wavenumber(cm ) Fig. 3 FT-IR spectra of (a) Pine pollen; (b) biochar; (c) MB; (d) MBA-3

The FT-IR spectrum of the prepared samples collected over 400–4000 cm-1 was disclosed (Fig. 3). The characteristic peaks at ~400 and 589 cm-1 corresponded to the Fe(III)–O and Co(II)–O bond of spinel-type oxide[25, 38]. A representative PO43- stretching vibration peak at 1016 cm-1 was also observed, which was a strong evidence for the successful preparation of MBA-3. The peaks at 1383 and 1631 cm-1 were the O–H bending vibrations of adsorbed water[30]. The absorption bands of the samples at 3435 cm-1 were ascribed to the O–H stretching vibration of adsorbed H2O

molecules in the composites[39]. It can be seen that the organic components in pine pollen are not completely lost after high temperature calcination, most of the oxygen-containing functional groups in natural biomass are still stable in biochar. The aforementioned result was in line with the XRD result above. It is worth noting that the characteristic peak intensity of Co–O in MBA-3 is relatively weak compared with MB, and the characteristic peak position of Fe–O moves to the low frequency direction (562 cm-1), which may be due to the introduction of Ag3PO4.

3.4 XPS analysis

(a)

Ag 3d

Intensity (a.u.)

O 1s Co 2p Fe 2p

C 1s

1200

1000

800

600

400

P 2p

200

0

Binding energy (eV) Co 2p3/2

(b)

Fe 2p3/2

Fe 2p1/2 716.95 eV 724.18 eV

785.86eV

711.87 eV

Satellite

Intensity (a.u.)

Intensity (a.u.)

Fe 2p

(c)

781.44eV

Co 2p1/2 797.27 eV

Co 2p

802.78 eV

Satellite 810

800

790 Binding energy (eV)

Ag 3d

367.72 eV

(d) Ag 3d3/2

740

780

730

720 Binding energy (eV)

710

700

P 2p

(e) 132.90 eV

Ag 3d5/2

Intensity (a.u.)

Intensity (a.u.)

373.73 eV

380

375

370 Binding energy (eV)

365

360

145

140

135 Binding energy (eV)

130

125

530.60 eV

(f)

O 1s

C 1s

(g)

284.35 eV

Intensity (a.u.)

Intensity (a.u.)

C=C

532.28eV（ -OH）

285.12 eV C-C 286.41 eV C-H

533.00 eV（ C=O）

540

535

287.78 eV C=O

530 Binding energy (eV)

525

295

290

285 Binding energy (eV)

280

Fig. 4 XPS spectra of MBA-3: (a) the survey scans, (b) Co 2p; (c) Fe 2p; (d) Ag 3d; (e) P 2p; (f) O 1s and (d) C 1s

To gain further insight of the surface element composition and chemistry state of the MBA-3, the XPS spectrum of the composite was employed (Fig.4). In Fig. 4a, the XPS survey (wide-scan) spectra confirm the existence of Ag, P, O, Co, Fe, and C in the MBA-3 composite. The XPS spectra of Co and Fe are shown in Figs. 4b and c. Both regions exhibit complex shake-up satellite structures arising from multiple interactions between the core hole generated on photoemission and the unpaired 3d valence electrons. These structures are characteristic peaks of high-spin Fe3+ and Co2+ centers[40]. Fig. 4c shows the Fe 2p region in which the peaks at 711.87 and 724.18 eV are attributable to the 2p3/2 and 2p1/2 spin orbit components. An additional peak at 716.95 eV, which is consistent with the literature, is assigned to the Fe3+ satellite transitions[41, 42]. Similarly, the Co spectra (Fig. 4b) are consistent with Co2+ peaks arising at 781.44 and 797.27 eV from the principal 2p3/2 and 2p1/2 transitions[43]. The satellite peaks around 785.86 and 802.78 eV are two shake-up type peaks of Co at the high binding energy side of the Co2p3/2 and Co2p1/2 edges. The presence of shake-up satellite peaks as well as Co2p3/2 and Co2p1/2 main peaks indicate the presence of Co2+ in the high-spin state[44]. The ratio of the satellite peaks to the main Fe 2p or Co 2p transitions are independent of particle size, suggesting no change in Fe 3+ or Co2+ content following high-temperature calcination. In Fig. 4d, the two individual peaks centered at the binding energies of 367.72 and 373.73 eV are related to Ag 3d5/2 and Ag 3d3/2, respectively, indicating that Ag+ is present in the samples. Only one peak centered at 132.90 eV is discovered and extremely corresponds to P5+ of PO43− in Ag3PO4 in Fig. 4e. In Fig. 4f, the peak of O 1s centered at the binding energy of 530.60 eV is consistent with the O 2− anion from the CoFe2O4 and Ag3PO4, whereas the peaks with the binding energies of 532.28 and 533.00 eV relate to O bonded to contaminated C (C−O, C=O)[45]. The C 1s peaks can be divided into four; those

located at 284.35, 285.12, 286.41, and 287.78 eV are assigned to C=C, C−C, C−OH, and C−O, respectively[8]. The aforementioned results are in agreement with the reference.

3.5 Optical absorption properties

(a)

0.8

(b)

Ag PO 3 4

1/2

0.6

1/2

(ahv) (eV)

Absorbance(a.u.)

MBA-3

0.4

Ag3PO4

0.2

200

CoFe2O4 Biochar

CoFe2O4/Ag3PO4 Biochar/Ag3PO4

MB

MBA-3

300

400

1.97 eV 537nm

500

600

2.35 eV

825nm 700

800

1.6

2.0

2.4

2.8

Wavelength(nm)

3.2

3.6

4.0

4.4

hv(eV)

Fig. 5 UV-vis absorption spectra of the prepared samples

To investigate the optical absorption properties of the photocatalysts, the UV–vis spectra are provided in Fig. 5. Ag3PO4 shows strong absorption within the range of visible light (390~760 nm), with an absorption edge around 537 nm (Fig. 5a). Interestingly, MBA-3 exhibited an apparently enhanced visible light absorption edge extending to 825 nm compared with Ag3PO4. The enhancement of the absorption of visible light may have a beneficial effect on forming more electron–hole pairs, thus improving the photocatalytic performance. The inferred value of the band gap energies (E g) can be obtained by extrapolation of the linear part of the curves obtained by plotting (ahv)2 versus hv in Fig. 5b. Accordingly, the E g of Ag3PO4 and MBA-3 were estimated to be 2.35 and 1.97 eV, respectively. It can be seen that the Eg of the MBA-3 composite is significantly smaller than Ag3PO4, and the visible light absorption capacity is enhanced[46]. This may be due to the interaction between MB and Ag3PO4 which increases the electron transfer of the interface, thereby improving the photocatalytic degradation efficiency[30].

3.6 BET analysis 160

MB MBA-3 Ag3PO4

140

CoFe2O4/Ag3PO4

100 80

3

Va/cm (STP)g

-1

120

60 40 20 0 0.0

0.2

0.4

0.6

0.8

1.0

P/P0 Fig. 6 N2 adsorption-desorption isotherms

The nitrogen adsorption-desorption isotherms and corresponding pore size distribution curves of the Ag3PO4, MB, CoFe2O4/Ag3PO4 and MBA-3 are displayed in Fig. 6. MB and MBA-3 have similar nitrogen adsorption-desorption isotherms of type IV, and their hysteresis loop are classified as H3. The specific surface areas of Ag3PO4, MB, CoFe2O4/Ag3PO4, and MBA-3 are 1.543, 83.771, 14.973 and 21.848 m2g-1, respectively. It is obvious that the specific surface area of the MBA-3 composite is larger than Ag3PO4 and CoFe2O4/Ag3PO4, less than MB. The specific surface area of the MBA-3 has a larger area increases because of the addition of MB, which also contributes to provide more active sites than the pure Ag3PO4[47], and the pollutants are more easily adsorbed on the surface of the catalytic material, thereby contributing to the enhancement of photocatalytic activity. Table 2 BET data of as-prepared samples Photocatalyst

Surface area(m2/g)

Pore volume(cm3/g)

Ag3PO4

1.543

0.007

MB

83.771

0.218

Ag3PO4/CoFe2O4

14.973

0.022

MBA-3

21.848

0.059

3.6 Analysis of separation efficiency of photogenerated carriers 800

MB Ag3PO4 MBA-3

-Z'' (ohm)

600

400

200

0 0

200

400

600

800

1000

Z' (ohm) Fig. 7 EIS of Nyquist plots of MB, Ag3PO4, MBA-3 electrodes in 0.01 M Na2SO4 aqueous solution

In order to analyze the separation efficiency of photo-generated carrier, electrochemical impedance spectroscopy (EIS) was collected in 0.01 M Na2SO4 aqueous solution. Generally, a smaller arc radius means that the resistance of surface charge transfer is weaker[48, 49]. The results in Fig. 7 display that the arc radius of MBA-3 is smaller than the arc radius of Ag3PO4 and MB, that is, the resistance of MBA-3 surface charge transfer is much smaller, which contributes to the separation of photogenerated electrons and holes. Meanwhile, the introduction of MB leads to a significantly decreased diameter of the semicircular Nyquist plot, which also suggests a quicker charge transfer in this Z-scheme photocatalytic system.

3.7 Photocatalytic activity 1.0

(b)

1.0

0.8

0.8

0.6

0.6

MBA-1 MBA-2 MBA-3 MBA-4 MBA-5 MBA-3(dark)

0.4

0.2

0.0 -30

-20

-10

0

Ag3PO4

C/C0

C/C0

(a)

CoFe2O4

0.4

MB CoFe2O4/ Ag3PO4 biochar/Ag3PO4

0.2

MB+Ag3PO4 MBA-3 10

20

30

Time (min)

40

50

60

70

0.0 -30

-20

-10

0

10

20

30

Time (min)

40

50

60

70

2.5 2

(c)

(d)

MBA-3 R =0.955 2 MB R =0.8973 2 MB+Ag3PO4 R =0.94939

2.0

1.0

0.8

2

CoFe2O4/ Ag3PO4 R =0.99681 2

TOC/TOC0

biochar/Ag3PO4 R =0.95996

1.5 ln(C0/C)

2

Ag3PO4 R =0.91595 2

CoFe2O4 R =0.95751

1.0

0.6

Ag3PO4 0.4

CoFe2O4 CoFe2O4/Ag3PO4

0.5

biochar/Ag3PO4

0.2

MB+Ag3PO4

0.0

MBA-3 0

10

20

30

40

50

60

0.0 -30

-20

Time (min)

-10

0

10

20

30

40

50

60

70

Time (min)

Fig. 8 (a,b) Photocatalytic degradation of BPA with different photocatalysts; (c) kinetic fit for the degradation of BPA with different photocatalysts; (d) TOC removal rate with different photocatalysts

The photocatalytic performances of different photocatalysts were evaluated by the degradation of BPA under visible light irradiation. As demonstrated in Fig. 8a, all of the MBA-m composites show enhanced adsorption and photocatalytic performance. Especially for the MBA-3, 91.12% of BPA was degraded within 60 min, which shows the highest activity. It can also be seen that the photocatalytic activity of MBA-3 is significantly higher than other photocatalysts in Fig. 8b. Furthermore, to compare the photocatalytic efficiency of the photocatalysts, the kinetic behaviors were investigated and shown in Fig. 8c. All of them are well suited to the pseudo-first-order kinetic model, which can be described by the following formula:

- ln(C / C 0 )  kappt

where C0, C, kapp, and t represent the initial concentration of BPA, the

concentration during the reaction, the first-order apparent rate constant and the reaction time, respectively. The trend of -ln(C/C0) was approximately linear with t. The kapp over the MBA-3 was 0.03411 min-1, being 4.9 times that of Ag3PO4 (0.007 min-1), and 44.9 times that of CoFe2O4 (0.000759652 min-1). The mineralization ability of the photocatalysts is vital to remove organic pollutants. As shown in Fig. 8d, the prepared MBA-3 obtained a TOC removal efficiency of 80.23% after 60min, which was higher than that of Ag3PO4 (25.98%) under similar conditions, indicating that MBA-3 presents enhanced mineralization ability.

3.8 Photocatalytic recyclability

(a) 100

MBA-3 Ag3PO4

(b)

MBA-3 Ag3PO4

80

80

TOC/TOC0

60

C/C0

60

40

40

20

20

0

0

st 1 run

2

nd

run

3

rd

run

4

th

run

st 1 run

2nd run

3rd run

4th run

Fig. 9 Photodegradation efficiency of BPA and TOC with MBA-3 after four cycles

In the practical applications, the recyclability of photocatalyst is an important parameter in evaluating photocatalysts. Therefore, a cycle experiment was employed to evaluate the activity and stability of the photocatalyst as shown in Fig. 9. After four cycling runs, the degradation efficiency of BPA and the removal rate of TOC can still reach 73.94% and 58.96%, respectively. Meanwhile, the photocatalytic activity of the single component was nearly inactivated. The aforementioned results demonstrate that the MBA-3 not only possesses the excellent photocatalytic stability but also has amazing stability compared with some previous reports[50-58], which can be due to the Z-scheme heterojunction between MB and Ag3PO4.

Fig. 10 XRD patterns of MBA-3 after four cycles

Furthermore, the XRD image of MBA-3 after 4 cycles was also given in Fig. 10. The Ag0 can be easily found in the XRD patterns of Ag3PO4 and MBA-3, which may be attributed to the photogenerated electrons of the CB cannot be transferred to the VB of the CoFe2O4 on time. The resulting structural instability is the main reason of the deterioration for MBA-3 after each

reaction. The good news is that although the current method is not enough to avoid the photocorrosion of Ag3PO4 completely, effective means such as the introduction of a magnetic medium can greatly improve the stability of the photocatalyst.

3.9 Magnetic separation performance study 16

MBA-3

Moment/Mass(emu/g)

12 8 4 0 -4 -8 -12 -16 -20000

-10000

0

10000

20000

Field(G) Fig. 11 Magnetic hysteresis loop of MBA-3

In general, since CoFe2O4 has excellent magnetic separation performance, it is presumed that the composite MBA-3 composed of CoFe2O4 also exhibits a good magnetic separation effect. To evaluate the magnetic property, the magnetic hysteresis loop of MBA-3 was depicted in Fig. 11. The saturation magnetic strength of the MBA-3 was 17.30 emu·g-1, which can meet the requirements to separate from suspension easily only by the additional magnetic field after being used in the photocatalytic process[8]. Not only the MBA-3 shows the excellent photocatalytic activity for the degradation of BPA, but also are easily to recycle from water environment.

3.10 Possible photocatalytic mechanism for BPA degradation

1.0

C/C0

0.8

0.6

0.4

No addition with 1mM IPA with 1mM BZQ with 1mM EDTA-2Na

0.2

0.0 -30

-20

-10

0

10

20

30

40

50

60

70

Time(min) Fig. 12 Photodegradation efficiency of BPA under different scavengers

It is well known that active species play an extremely important role in the photocatalytic degradation of organic pollutions[59]. The active species and electron transfer mechanism during the photocatalytic reaction are verified by investigating the roles of three common active oxidant species, namely, hydroxyl radical (·OH), hole (h+), and superoxide radical (·O2-). Select EDTA-2Na, IPA and BZQ as capture agents for h+, ·OH and ·O2-, respectively. Results of free radical trapping experiments are shown in Fig. 12. The addition of 1 mM EDTA-2Na significantly inhibited the photodegradation efficiency of BPA. The removal efficiency of BPA was only 11.25%, which indirectly reflected the inhibition efficiency of 78.89%. Similarly, when BZQ or IPA was added, its inhibition efficiency against BPA was 50.34% and 6.69%, respectively. This result indicates that during this process, h+ and ·O2- are the main active species of the reaction system, whereas ·OH contributes minimally.

3.11 Possible intermediate of BPA photodegradation and degradation pathway In order to speculate on the probable intermediate products generated during the photocatalytic degradation of BPA, GC-MS was performed. Five probable intermediate products were identified by comparing with the NIST 17.1 library, which were list in Table 3. Based on the intermediates detected by GC-MS, a possible pathway of BPA degradation by MBA-3 was proposed and shown in Fig. 13. In the photocatalytic reaction, BPA was adsorbed to the surface of the photocatalyst firstly, next converted into a monocyclic organic substance by the direct oxidation, and then the

ring was opened to form a chain, finally converted into CO 2 and H2O[60]. In addition, the Z-scheme heterojunction between MB and Ag3PO4 also accelerate the migration of the electron and hole pairs, thereby increasing the mineralization rate. Table 3 GC-MS data of the photodegradation products of BPA by MBA-3 Compounds

Structures

Retention time (min)

m/z

BPA

39.486

228

Toluene

4.338

92

Ethylbenzene

6.969

106

o-Xylene

7.206

106

Cyclohexanone

7.961

98

2,4-Di-tert-butylphenol

25.880

206

Fig. 13 possible degradation pathway of BPA

On the basis of the results discussed above, a possible Z-scheme photocatalytic mechanism of MBA-3 for BPA degradation is proposed and illustrated in Fig. 14. Under visible light illumination, the photogenerated electrons and holes in Ag3PO4 are rapidly excited and generated on their respective CB and VB. Biochar can assist e- to move from the CB of Ag3PO4 to the VB of CoFe2O4 and then to the CB of CoFe2O4 due to its electrical conductivity. This movement greatly promotes the separation of photogenerated electron−hole pairs. Most of the accumulated h+ on the VB of Ag3PO4 and CoFe2O4 have strong oxidizing power themselves and can directly oxidize BPA molecules into inorganic substances or other intermediate products. According to Mulliken’s theory of electronegativity theory, the CB of Ag3PO4 cannot produce ·O2- because the ECB of Ag3PO4 (0.29 eV/NHE) exhibits a more positive potential compared with that of O 2/·O2- (-0.33 eV/NHE)[61]. The remaining e- on the CB of CoFe2O4 can produce ·O2- by absorbing O 2. It is

worth mentioning that PFRs in biochar can induce oxygen to produce ·O2-, which will contribute to the enhancement of photocatalytic performance[27]. The h+ on the VB of CoFe2O4 cannot combine with H2O molecules and OH- to form ·OH because the EVB of CoFe2O4 (2.12 eV/NHE) is more negative than OH-/·OH (2.4 eV/NHE). In the Z-scheme system, h+, ·O2- and ·OH are involved in the degradation of BPA, which has been proven to exist in trapping experiments. Thus, a visible-light photocatalyst based on the biochar@CoFe2O4/Ag3PO4 follows a Z-scheme photocatalytic mechanism, which effectively suppresses the recombination of electron−hole pairs and improves photocatalytic performance. This method lays a foundation for its application in practical wastewater treatment.

Fig. 14 Photocatalytic mechanism scheme and charge transfer of the MBA-3.

4. Conclusions

A novel Z-scheme photocatalyst based on biochar@CoFe2O4/Ag3PO4 was prepared by a facile method successfully. When BPA was selected as the target pollution, the degradation efficiency and mineralization rate within 60 min could reach to 91.12% and 80.23%, respectively. The results of free radical trapping experiments indicates that h+ and ·O2- are the main active species of the reaction system. At the same time, we proposed the Z-scheme photocatalytic mechanism for highly efficient degradation of BPA and the possible photodegradation pathway of BPA is also suggested. Moreover, the photocatalysts are also easily to recycle for reuse from water bodies, avoiding secondary pollution effectively. Thus, the present study has provided a valuable way to design new and efficient system for organic pollutions degradation in waste water.

Acknowledgments The authors gratefully acknowledge the financial support provided by the Hunan Provincial Science and Technology Plan Project (No. 2018SK2021).

References [1] L. Luo, Y. Yang, M. Xiao, L. Bian, B. Yuan, Y. Liu, F. Jiang, X. Pan, A novel biotemplated synthesis of TiO2/wood charcoal composites for synergistic removal of bisphenol A by adsorption and photocatalytic degradation, Chemical Engineering Journal, 262 (2015) 1275-1283. [2] S.M. Arnold, K.E. Clark, C.A. Staples, G.M. Klecka, S.S. Dimond, N. Caspers, S.G. Hentges, Relevance of drinking water as a source of human exposure to bisphenol A, J Expo Sci Environ Epidemiol, 23 (2013) 137-144. [3] H. Zhang, J. Shi, X. Liu, X. Zhan, Q. Chen, Occurrence and removal of free estrogens, conjugated estrogens, and bisphenol A in manure treatment facilities in East China, Water Research, 58 (2014) 248-257. [4] Y. Liu, G. Zhu, J.Z. Gao, M. Hojamberdiev, H. Lu, R. Zhu, X. Wei, P. Liu, A novel CeO2/Bi4Ti3O12 composite heterojunction structure with an enhanced photocatalytic activity for bisphenol A, (2016). [5] A. Colombo, G. Cappelletti, I. Biraghi, C.L. Bianchi, D. Meroni, C. Pirola, F. Spadavecchia, Bisphenol A endocrine disruptor complete degradation using TiO photocatalysis with ozone, Environmental Chemistry Letters, 10 (2012) 55-60. [6] J. Qu, C. Luo, X. Yuan, Synthesis of hybrid carbon nanotubes using Brassica juncea L. application to photodegradation of bisphenol A, Environ Sci Pollut Res Int, 20 (2013) 3688-3695. [7] Y. Xi, Z. Sun, T. Hreid, G.A. Ayoko, R.L. Frost, Bisphenol A degradation enhanced by air bubbles via advanced oxidation using in situ generated ferrous ions from nano zero-valent iron/palygorskite composite materials, Chemical Engineering Journal, 247 (2014) 66-74. [8] X. Chen, Y. Dai, T. Liu, J. Guo, X. Wang, F. Li, Magnetic core–shell carbon microspheres (CMSs)@ZnFe2O4/Ag3PO4 composite with enhanced photocatalytic activity and stability under visible light irradiation, Journal of Molecular Catalysis A: Chemical, 409 (2015) 198-206. [9] J. Guo, Y.-z. Dai, X.-j. Chen, L.-l. Zhou, T.-h. Liu, Synthesis and characterization of Ag3PO4/LaCoO3 nanocomposite with superior mineralization potential for bisphenol A degradation under visible light, Journal of Alloys and Compounds, 696 (2017) 226-233. [10] J. Yan, Z. Song, X. Wang, Y. Xu, W. Pu, H. Xu, S. Yuan, H. Li, Enhanced photocatalytic activity of ternary Ag3PO4/GO/g-C3N4 photocatalysts for Rhodamine B degradation under visible light radiation, Applied Surface Science, 466 (2019) 70-77. [11] L. Zhou, W. Zhang, L. Chen, H. Deng, Z-scheme mechanism of photogenerated carriers for hybrid photocatalyst Ag3PO4/g-C3N4 in degradation of sulfamethoxazole, Journal of Colloid & Interface Science, 487 (2017) 410-417. [12] Y. Yu, J. Geng, H. Li, R. Bao, H. Chen, W. Wang, J. Xia, W.-Y. Wong, Exceedingly high photocatalytic activity of g-C 3 N 4 /Gd-N-TiO 2 composite with nanoscale heterojunctions, Solar Energy Materials

and Solar Cells, 168 (2017) 91-99. [13] Y. Li, Y. Xue, J. Tian, X. Song, X. Zhang, X. Wang, H. Cui, Silver oxide decorated graphitic carbon nitride for the realization of photocatalytic degradation over the full solar spectrum: From UV to NIR region, Solar Energy Materials and Solar Cells, 168 (2017) 100-111. [14] X. Chen, Y. Dai, X. Wang, Methods and mechanism for improvement of photocatalytic activity and stability of Ag3PO4: A review, Journal of Alloys and Compounds, 649 (2015) 910-932. [15] G. Jianjun, Z. Han, O. Shuxin, K. Tetsuya, Y. Jinhua, An Ag3PO4/nitridized Sr2Nb2O7 composite photocatalyst with adjustable band structures for efficient elimination of gaseous organic pollutants under visible light irradiation, Nanoscale, 6 (2014) 7303-7311. [16] Y. Liu, F. Liang, H. Lu, Y. Li, C. Hu, H. Yu, One-pot pyridine-assisted synthesis of visible-light-driven photocatalyst Ag/Ag 3 PO 4, Applied Catalysis B Environmental, 115-116 (2012) 245-252. [17] B. Cao, P. Dong, C. Shuai, Y. Wang, BiOCl/Ag3PO4 Composites with Highly Enhanced Ultraviolet and Visible Light Photocatalytic Performances, Journal of the American Ceramic Society, 96 (2013) 544-548. [18] Z.K. Cui, F.L. Zhang, Z. Zheng, W.J. Fa, B.J. Huang, Preparation and characterisation of Ag3PO4/BiOBr composites with enhanced visible light driven photocatalytic performance, Materials & Processing Report, 29 (2015) 214-219. [19] Y. Wang, X. Cheng, X. Meng, H. Feng, S. Yang, S. Cheng, Preparation and characterization of Ag 3 PO 4 /BiOI heterostructure photocatalyst with highly visible-light-induced photocatalytic properties, Journal of Alloys & Compounds, 632 (2015) 445-449. [20] B. Yingpu, O. Shuxin, C. Junyu, Y. Jinhua, Facile synthesis of rhombic dodecahedral AgX/Ag3PO4 (X = Cl, Br, I) heterocrystals with enhanced photocatalytic properties and stabilities, Physical Chemistry Chemical Physics Pccp, 13 (2011) 10071-10075. [21] G. Chen, M. Sun, Q. Wei, Y. Zhang, B. Zhu, B. Du, Ag3PO4/graphene-oxide composite with remarkably enhanced visible-light-driven photocatalytic activity toward dyes in water, Journal of Hazardous Materials, 244-245 (2013) 86-93. [22] X. Liu, J. Xu, Z. Ni, R. Wang, J. You, R. Guo, Adsorption and visible-light-driven photocatalytic properties of Ag3PO4/WO3 composites: A discussion of the mechanism, Chemical Engineering Journal, 356 (2019) 22-33. [23] X. Ma, H. Li, Y. Wang, H. Li, B. Liu, S. Yin, T. Sato, X. Ma, H. Li, Y. Wang, Substantial change in phenomenon of "self-corrosion" on Ag3PO4/TiO2 compound photocatalyst, Applied Catalysis B Environmental, 158-159 (2014) 314-320. [24] L. Zhang, D. Yu, M. Wu, J. Lin, Fabrication of Ag3PO4/TiO2 Composite and Its Photodegradation of Formaldehyde Under Solar Radiation, 149 (2019). [25] E. Abroushan, S. Farhadi, A. Zabardasti, Ag3PO4/CoFe2O4 magnetic nanocomposite: synthesis, characterization and applications in catalytic reduction of nitrophenols and sunlight-assisted photocatalytic degradation of organic dye pollutants, RSC Advances, 7 (2017) 18293-18304. [26] M. Li, H. Huang, S. Yu, N. Tian, F. Dong, X. Du, Y. Zhang, Simultaneously promoting charge separation and photoabsorption of BiOX (X=Cl, Br) for efficient visible-light photocatalysis and photosensitization by compositing low-cost biochar, Applied Surface Science, 386 (2016) 285-295. [27] G. Fang, C. Zhu, D.D. Dionysiou, J. Gao, D. Zhou, Mechanism of hydroxyl radical generation from biochar suspensions: Implications to diethyl phthalate degradation, Bioresource Technology, 176 (2015) 210-217. [28] K. Tang, R.J. White, X. Mu, M.M. Titirici, P.A. van Aken, J. Maier, Hollow carbon nanospheres with

a high rate capability for lithium-based batteries, Chemsuschem, 5 (2012) 400-403. [29] Q. Wang, H. Li, L. Chen, X. Huang, Monodispersed hard carbon spherules with uniform nanopores, Carbon, 39 (2001) 2211-2214. [30] Y. Xie, Y. Dai, X. Yuan, L. Jiang, L. Zhou, Z. Wu, J. Zhang, H. Wang, T. Xiong, Insight on the plasmonic Z-scheme mechanism underlying the highly efficient photocatalytic activity of silver molybdate/silver vanadate composite in rhodamine B degradation, J Colloid Interface Sci, 530 (2018) 493-504. [31] T. Zhou, G. Zhang, H. Zhang, H. Yang, P. Ma, X. Li, X. Qiu, G. Liu, Highly efficient visible-light-driven photocatalytic degradation of rhodamine B by a novel Z-scheme Ag3PO4/MIL-101/NiFe2O4 composite, Catalysis Science & Technology, 8 (2018) 2402-2416. [32] R. Jiang, H.Y. Zhu, J.B. Li, F.Q. Fu, J. Yao, S.T. Jiang, G.M. Zeng, Fabrication of novel magnetically separable BiOBr/CoFe2O4 microspheres and its application in the efficient removal of dye from aqueous phase by an environment-friendly and economical approach, Applied Surface Science, 364 (2016) 604-612. [33] F. Xiao, J. Cheng, W. Cao, C. Yang, J. Chen, Z. Luo, Removal of heavy metals from aqueous solution using chitosan-combined magnetic biochars, Journal of Colloid and Interface Science, 540 (2019) 579-584. [34] X. Miao, X. Yue, Z. Ji, X. Shen, H. Zhou, M. Liu, K. Xu, J. Zhu, G. Zhu, L. Kong, S.A. Shah, Nitrogen-doped carbon dots decorated on g-C3N4/Ag3PO4 photocatalyst with improved visible light photocatalytic activity and mechanism insight, Applied Catalysis B: Environmental, 227 (2018) 459-469. [35] Z. Wang, W. Jia, M. Jiang, C. Chen, Y. Li, One-step accurate synthesis of shell controllable CoFe2O4 hollow microspheres as high-performance electrode materials in supercapacitor, Nano Research, 9 (2016) 2026-2033. [36] H. Fu, S. Ma, P. Zhao, S. Xu, S. Zhan, Activation of peroxymonosulfate by graphitized hierarchical porous biochar and MnFe2O4 magnetic nanoarchitecture for organic pollutants degradation: Structure dependence and mechanism, Chemical Engineering Journal, 360 (2019) 157-170. [37] H. Hu, S. Cai, H. Li, L. Huang, L. Shi, D. Zhang, In Situ DRIFTs Investigation of the Low-Temperature Reaction Mechanism over Mn-Doped Co3O4 for the Selective Catalytic Reduction of NOx with NH3, The Journal of Physical Chemistry C, 119 (2015) 22924-22933. [38] V.S. Kumbhar, A.D. Jagadale, N.M. Shinde, C.D. Lokhande, Chemical synthesis of spinel cobalt ferrite (CoFe2O4) nano-flakes for supercapacitor application, Applied Surface Science, 259 (2012) 39-43. [39] J.-H. Yuan, R.-K. Xu, H. Zhang, The forms of alkalis in the biochar produced from crop residues at different temperatures, Bioresource Technology, 102 (2011) 3488-3497. [40] N. Ballarini, F. Cavani, S. Passeri, L. Pesaresi, A.F. Lee, K. Wilson, Phenol methylation over nanoparticulate CoFe2O4 inverse spinel catalysts: The effect of morphology on catalytic performance, Applied Catalysis A: General, 366 (2009) 184-192. [41] G. Bhargava, I. Gouzman, C.M. Chun, T.A. Ramanarayanan, S.L. Bernasek, Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study, Applied Surface Science, 253 (2007) 4322-4329. [42] T. Droubay, S.A. Chambers, Surface-sensitive Fe 2p photoemission spectra for α-Fe2O3(0001): The influence of symmetry and crystal-field strength, Phys.rev.b, 64 (2001) 205414. [43] K. Takubo, T. Mizokawa, S. Hirata, J.Y. Son, A. Fujimori, D. Topwal, D.D. Sarma, S. Rayaprol, E.V. Sampathkumaran, Electronic structure of Ca 3 Co X O 6 ( X = Co , Rh, Ir) studied by x-ray

photoemission spectroscopy, Phys.rev.b, 71 (2005) 3406. [44] W. Bian, Z. Yang, P. Strasser, R. Yang, A CoFe2O4/graphene nanohybrid as an efficient bi-functional electrocatalyst for oxygen reduction and oxygen evolution, Journal of Power Sources, 250 (2014) 196-203. [45] Q. Chen, Q. Wu, Preparation of carbon microspheres decorated with silver nanoparticles and their ability to remove dyes from aqueous solution, Journal of Hazardous Materials, 283 (2015) 193-201. [46] S. Perween, A. Ranjan, Improved visible-light photocatalytic activity in ZnTiO3 nanopowder prepared by sol-electrospinning, Solar Energy Materials and Solar Cells, 163 (2017) 148-156. [47] J. Ma, Q. Liu, L. Zhu, J. Zou, K. Wang, M. Yang, S. Komarneni, Visible light photocatalytic activity enhancement of Ag 3 PO 4 dispersed on exfoliated bentonite for degradation of rhodamine B, Applied Catalysis B: Environmental, 182 (2016) 26-32. [48] Y. He, L. Zhang, B. Teng, M. Fan, New Application of Z-Scheme Ag3PO4/g-C3N4 Composite in Converting CO2 to Fuel, Environmental Science & Technology, 49 (2015) 649-656. [49] W. Teng, X. Li, Q. Zhao, G. Chen, Fabrication of Ag/Ag3PO4/TiO2 heterostructure photoelectrodes for Efficient Decomposition of 2-chlorophenol Under Visible Light Irradiation, Journal of Materials Chemistry A, 1 (2013) 9060-9068. [50] C. Chang, L. Zhu, Y.U. Fu, X. Chu, Highly active Bi/BiOI composite synthesized by one-step reaction and its capacity to degrade bisphenol A under simulated solar light irradiation, Chemical Engineering Journal, 233 (2013) 305-314. [51] S. Huang, Y. Xu, X. Meng, Q. Liu, H. Li, A Z-scheme magnetic recyclable Ag/AgBr@CoFe 2 O 4 photocatalyst with enhanced photocatalytic performance for pollutant and bacterial elimination, Rsc Advances, 7 (2017) 30845-30854. [52] J. Liang, F. Liu, M. Li, W. Liu, M. Tong, Facile synthesis of magnetic Fe3O4@BiOI@AgI for water decontamination with visible light irradiation: Different mechanisms for different organic pollutants degradation and bacterial disinfection, Water Research, 137 (2018) 120-129. [53] X. Mao, C. Fan, Y. Wang, Y. Wang, X. Zhang, RhB-sensitized effect on the enhancement of photocatalytic activity of BiOCl toward bisphenol-A under visible light irradiation, Applied Surface Science, 317 (2014) 517-525. [54] W.-D. Oh, L.-W. Lok, A. Veksha, A. Giannis, T.-T. Lim, Enhanced photocatalytic degradation of bisphenol A with Ag-decorated S-doped g-C3N4 under solar irradiation: Performance and mechanistic studies, Chemical Engineering Journal, 333 (2018) 739-749. [55] M.E. Taheri, A. Petala, Z. Frontistis, D. Mantzavinos, D.I. Kondarides, Fast photocatalytic degradation of bisphenol A by Ag3PO4/TiO2 composites under solar radiation, Catalysis Today. [56] Y. Wang, Z. Xu, C. Di, W. Yan, Y. Zhu, Peroxymonosulfate enhanced visible light photocatalytic degradation bisphenol A by single-atom dispersed Ag mesoporous g-C3N4 hybrid, Applied Catalysis B Environmental, 211 (2017) 79-88. [57] Y. Xu, F. Ge, M. Xie, S. Huang, J. Qian, H. Wang, M. He, H. Xu, H. Li, Fabrication of magnetic BaFe12O19/Ag3PO4 composites with an in situ photo-Fenton-like reaction for enhancing reactive oxygen species under visible light irradiation, Catalysis Science & Technology, 9 (2019). [58] Y. Xu, S. Huang, X. Meng, Y. Li, L. Jing, H. Xu, Z. Qi, H. Li, Core-shell magnetic Ag/AgCl@Fe2O3 photocatalyst with enhanced photoactivity in eliminating the bisphenol A and microbial contamination, New Journal of Chemistry, 40 (2016) 3413-3422. [59] X.Q. Liu, W.J. Chen, H. Jiang, Facile synthesis of Ag/Ag 3 PO 4 /AMB composite with improved photocatalytic performance, Chemical Engineering Journal, 308 (2017) 889-896.

[60] C. Wang, J. Zhu, X. Wu, H. Xu, Y. Song, J. Yan, Y. Song, H. Ji, K. Wang, H. Li, Photocatalytic degradation of bisphenol A and dye by graphene-oxide/Ag3PO4 composite under visible light irradiation, Ceramics International, 40 (2014) 8061-8070. [61] X. Yuan, L. Jiang, X. Chen, L. Leng, H. Wang, Z. Wu, T. Xiong, L. Jie, G. Zeng, Highly efficient visible-light-induced photoactivity of Z‑ scheme Ag2CO3/Ag/WO3 photocatalysts for organic pollutant degradation, Environmental Science Nano, 4 (2017) 10.1039.C1037EN00713B.