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ISSN : 1225-0562(Print)
ISSN : 2287-7258(Online)
Korean Journal of Materials Research Vol.30 No.8 pp.383-392
DOI : https://doi.org/10.3740/MRSK.2020.30.8.383

Preparation of AgCl/Ag3PO4/Diatomite Composite by Microemulsion Method for Rapid Photo-Degradation of Rhodamine B with Stability under Visible Light

Hai-Tao Zhu1, Qi-Fang Ren1, Zhen Jin1, Yi Ding1,2, Xin-Yu Liu2, Xi-Hui Ni2, Meng-Li Han2, Shi-Yu Ma2, Qing Ye2, Won-Chun Oh3
1Anhui Advanced Building Materials Engineering Laboratory, Anhui Jianzhu University, Hefei 230601, Anhui, China
2Key Laboratory of Huizhou Architecture in Anhui Province, Anhui Jianzhu University, Hefei 230022, Anhui, China
3Department of Advanced Materials Science & Engineering, Hanseo University, Seosan 31962, Republic of Korea
Corresponding author E-Mail : dyrqf@ahjzu.edu.cn (Y. Ding, Anhui Jianzhu Univ.) wc_oh@hanseo.ac.kr (W.-C. Oh, Hanseo Univ.)
June 10, 2020 July 8, 2020 July 14, 2020

Abstract

In this paper, AgCl/Ag3PO4/diatomite photocatalyst is successfully synthesized by microemulsion method and anion in situ substitution method. X-ray diffraction (XRD), photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy (UV-Vis) are used to study the structural and physicochemical characteristics of the AgCl/Ag3PO4/diatomite composite. Using rhodamine B (RhB) as a simulated pollutant, the photocatalytic activity and stability of the AgCl/Ag3PO4/diatomite composite under visible light are evaluated. In the AgCl/Ag3PO4/diatomite visible light system, RhB is nearly 100 % degraded within 15 minutes. And, after five cycles of operation, the photocatalytic activity of AgCl/Ag3PO4/diatomite remains at 95 % of the original level, much higher than that of pure Ag3PO4 (40 %). In addition, the mechanism of enhanced catalytic performance is discussed. The high photocatalytic performance of AgCl/Ag3PO4/diatomite composites can be attributed to the synergistic effect of Ag3PO4, diatomite and AgCl nanoparticles. Free radical trapping experiments are used to show that holes and oxygen are the main active species. This material can quickly react with dye molecules adsorbed on the surface of diatomite to degrade RhB dye to CO2 and H2O. Even more remarkably, AgCl/Ag3PO4/diatomite can maintain above 95 % photo-degradation activity after five cycles.


초록


    Anhui Jianzhu University

    © Materials Research Society of Korea. All rights reserved.

    This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

    1. Introducition

    In recent years, semiconductor photocatalytic technology has received extensive attention due to its direct use of solar energy to efficiently degrade organic dyes in sewage.1,2) As a highly efficient visible light photocatalyst, silver phosphate (Ag3PO4) has a band gap of only 2.46 eV and has p-type semiconductor characteristics.3-5) Under visible light, it can decompose water to produce oxygen and exhibit high photooxidation ability to organic pollutants in water. The ultraviolet-diffuse reflectance spectrum showed that silver phosphate could absorb sunlight with wavelength less than 530 nm, but its photo-corrosion effect was also very significant.6-8) The photogenerated electrons e- produced under the conditions of light easily combine with Ag+ to form Ag0, which caused the catalyst to be deactivated.3) So far, people have been working to improve the photocatalytic performance and stability of Ag3PO4, further coupling with other semiconductors to form hybrid complexes,9) doping heteroatoms,10) and adjusting morphology.4) Despite these strategies, supported cocatalysts are considered effective due to their ability to suppress the rate of charge carrier recombination.11,12) For example, Ag3PO4/Mn3O4/MnO2,13) Ag3PO4/Ag/BiVO4,14) Ag3PO4/g-C3N4,15,16) Ag3PO4@MWCNTs@PANI,1) etc, these composite materials successfully improved the stability of Ag3PO4 and further enhanced the photocatalytic efficiency of Ag3PO4. As a photosensitive material of 3.25 eV, AgCl was considered to be a good photocatalyst. AgCl nanoparticles could generate electron-hole pairs under illumination,17) and then electrons migrate to the AgCl surface to combine with Ag+ to form elemental Ag0. The light response interval of AgCl was further extended to the visible light region.18) Many researchers have coupled different semiconductors to AgCl to improve their photocatalytic activity and stability. For example, AgCl/AgI,19) Ag@AgCl/g-C3N4,20) Cu2O/Ag/AgCl,21) Ag/ AgCl/TiO222) and Ag/AgCl/WO323) have been reported.

    Diatomite (Dt) is a green and natural porous mineral material. Its main chemical component is amorphous SiO2. It has large specific surface area, excellent adsorption performance and low price.24) These conditions make diatomite a new darling decoration industry in China. However, the adsorbed air pollutants eventually reach saturation and are discharged into the air again, which hindered the large-scale application of diatomite. At present, the widely used method is compound ed catalysts with diatomite, many researches have shown that the combination of diatomite material with large specific surface area and photocatalytic semiconductor nanoparticles could improve the degradation, thereby effectively removing pollutants. Such as Wang et al. successfully immobilized TiO2 on diatomite using a modified sol-gel method without severe clogging on the surface of diatomite,25) Zhang et al. added diatomite powder to a solution containing Cu2+ by heating in a water bath, and then added a certain amount of CH3CSNH2 and stirred, then Cu2-xS/diatomite was obtained,26) Tanniratt et al. succeeded in immobilizing ZnO particles on diatomite by immersing diatomite powder in a precursor solution containing various zinc oxides.27) Our group prepared a Ag/Ag3PO4/diatomite composite photocatalyst by deposition-hydrothermal-photoreduction method.28)

    In this paper, AgCl/Ag3PO4/diatomite, a high-performance composite photocatalyst, was prepared using the microemulsion method. The composition, morphology, structure, and optical properties of the prepared samples were characterized. The method of degrading rhodamine B (RhB) dye under visible light irradiation was used to evaluate the photocatalytic performance and stability of the composites. And the corresponding degradation mechanism was proposed in combination with the free radical capture test.

    2. Experimental

    2.1 Experiment material

    The natural diatomite in this study was purchased from Linjiang Beifeng Diatomite Co., Ltd.; all chemical reagents were analytical grade except diatomite, purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai); experimental water was homemade distilled water.

    2.2 Material synthesis

    2.2.1 Diatomite pretreatment

    The diatomite was purified correspondingly according to the method of Fan et al.28) A certain amount of diatomite was mixed with a 20 % H2SO4 solution in an appropriate ratio. After magnetically stirring for 4 hours, it was repeatedly washed with distilled water to neutral. The material was filtered, dried, and heated at 600 °C for two hours, and then removed to natural cooling to obtain purified diatomite.

    2.2.2 Preparation of AgCl/Ag3PO4/diatomite

    An anion in situ substitution method was used to prepare the AgCl/Ag3PO4/diatomite composite. Three microemulsions with different aqueous phases were prepared, containing 6.0 mmol AgNO3 and 0.21 g diatomite (microemulsion A), 2 mmol NaH2PO4 × 2H2O (microemulsion B) and 0.187 mmol NH4Cl (microemulsion C) (note these microemulsions were prepared by mixing 1.39 mmol of SDS, 5 ml of cyclohexane and 1 ml of n-butanol as the oil phase, and 3 ml of ultrapure water as the water phase). Microemulsion B is then mixed with microemulsion A. The reaction was allowed to react for 0.5 h under rapid stirring under dark conditions to obtain an Ag3PO4/diatomite precursor. Then, microemulsion C was slowly added, stirred vigorously for 1 h, and left to mature. After the reaction was completed, demulsification and centrifugation were performed directly. The obtained product was washed with deionized water and anhydrous ethanol six times alternately, and dried in an oven at 70 °C for 12 h to obtain an AgCl/Ag3PO4/diatomite composite (AgCl/APO/ Dt). Under the same conditions, Ag3PO4/diatomite (APO/ Dt), Ag3PO4(APO), AgCl/Ag3PO4 (AgCl/APO), AgCl/ diatomite (AgCl/Dt), and AgCl powder samples were used as controls.

    2.3 Characterizations

    The phase of the sample was identified by TD-3000 (Dandong) X-ray diffractometer, and the 2θ angle measurement range was 10 ~ 70°. The microscopic morphology of the sample was observed with a JSM-7500F (JEOL) cold field emission scanning electron microscope (SEM). Transmission electron microscopy (TEM) observation of the sample was performed on a JEOL-2010 transmission electron microscope with an acceleration voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) analysis is carried out with ESCALAB-250 system. Solid UV-Vis spectroscopy was performed on a SP-752 spectrophotometer with a measurement range of 200 to 800 nm.

    2.4 Photocatalytic activity study

    The photocatalytic experiment was carried out using a 500 W xenon lamp with a 420 nm cut-off filter as the light source and Rhodamine B (RhB) as the organic pollutant model. The visible light catalytic activity was evaluated by testing the ability of the sample to degrade RhB under visible light irradiation. The catalytic effect of the catalyst was characterized by the change in concentration of RhB. During the illumination, 4 mL solution was withdrawn and centrifuged repeatedly at given intervals of time, and then the concentration test of dye was used by Metash UV-Vis spectrophotometer (UV- 5500PC). The specific steps are as follows: First 0.05 g of photocatalyst is placed in 100 mL of RhB aqueous solution (20 mg/L), and then stirred under dark conditions for 30 min to establish an adsorption-desorption equilibrium; about 4 mL is taken at regular intervals. The reaction solution was centrifuged, and the supernatant was taken and its absorbance at 554 nm was measured by an ultraviolet spectrophotometer. Three typical reagents, EDTA, BQ, and IPA were introduced as the scavengers of h+, superoxide radical (·O2) and hydroxyl radical (-OH), respectively. In details, 1 mmol of EDTA, BQ or IPA were added to the photocatalytic system in the photodegradation by AgCl/Ag3PO4/diatomite composite, respectively.

    3. Results and Discussion

    3.1 Characterization of the samples

    3.1.1 XRD analysis

    Fig. 1 showed the XRD diagrams of diatomite, AgCl, Ag3PO4, Ag3PO4/diatomite and AgCl/Ag3PO4/diatomite, respectively. From XRD pattern of diatomite [Fig. 1(a)], the diffraction peak of SiO2 located at 26.7° could be observed, indicating the main component of SiO2, which is consistent with the main phase of non-crystalline opal- A.29,30) For pure AgCl pattern in Fig. 1(b), the diffraction patterns could be assigned to the cubic phase of crystalline AgCl (JCPDS file No. 31-1238) (27.8°, 32.3°, 46.3°, 54.9°, 55.6° and 67.4°).31,32) As for the pure Ag3PO4 [Fig. 1(c)], all peaks of Ag3PO4 were corresponded to the cubic crystal structure according to the standard card (JCPDS 06-0505), the diffraction peaks at 21.0°, 29.8°, 33.5°, 36.7°, 42.6°, 47.8°, 52.7°, 54.9°, 57.3°, and 61.7° respectively corresponded to the (110), (200), (210), (211), (220), (310), (222), (320), (321), and (400) planes of Ag3PO4.9,33) Therefore, it could be confirmed that the prepared samples are all Ag3PO4 crystals with bodycentered cubic structure. In the XRD pattern of Ag3PO4/ diatomite composites [Fig. 1(d)], Only the characteristic diffraction peaks of Ag3PO4 were observed, which may be due to the lower diatomite content and poor crystallinity. At the same time, it was also shown that in the case of adding diatomite, the crystal phase formation of Ag3PO4 was not affected by the diatomite loading. The XRD pattern of AgCl/Ag3PO4/diatomite [Fig. 1(e)]. The addition of AgCl does not change the peak position of Ag3PO4, indicating that AgCl particles are deposited on the surface of Ag3PO4 instead of being incorporated into its lattice. And the addition of low content of diatomite did not affect the crystallization of AgCl/ Ag3PO4.

    3.1.2 XPS analysis

    XPS can be used to study the chemical composition and valence states of catalysts. Fig. 2(a) showed the XPS survey spectrum of AgCl/Ag3PO4/diatomite. The photoelectron peaks of Ag, Cl, P, Si and O are clearly discernible. Fig. 2(b-f) showed the high-resolution XPS spectra of Ag, Cl, P, Si and O, respectively. In the Ag 3d spectrum [Fig. 2(b)], the Ag 3d gave rise to two individual peaks located at 367.73 and 373.73 eV, corresponding to Ag 3d5/2 and Ag 3d3/2 orbitals typical of Ag+ respectively, which suggested that the Ag element is +1 in the AgCl/ Ag3PO4/diatomite composite.30,34) Fig. 2(c) showed the spectrum of Cl 2p, and the binding energies at 197.80 and 199.32 eV could be ascribed to Cl 2p3/2 and Cl 2p1/2, respectively.31,35) The P 2p spectrum in Fig. 2(d) demonstrated a peak centered at 133.46 eV owing to the presence of P5+ in Ag3PO4. 6,15) In the Si 2p spectrum [Fig. 2(e)], the main peak at 102.98 eV was attributed to diatomite.36) As shown in Fig. 2(f), the O 1s in Ag3PO4 sample could be divided into three individual peaks. One peak at 531.33.4 eV was corresponding to P-O in Ag3PO4,1) and that at 533.21 eV was ascribed to Si-O-Si in diatomite.36) In addition, another peak at 532.23 eV was found, which was attributed to the -OH group on the surface.16)

    3.1.3 SEM and EDS analysis

    The morphology and microstructure of the as-prepared photocatalysts were shown in Fig. 3. The SEM image in Fig. 3(a) indicated that diatomite exhibits a disk-like shape with a great number of the regular and clear pore structures on its surface, which was conducive to the adsorption of dye molecules.28,37) As shown in Fig. 3(bc), pure AgCl particles prepared by the microemulsion method were round with smooth surface and sizes of 200-500 nm, but its agglomeration phenomenon was serious,17) the Ag3PO4 particles prepared have a large size difference, Shapes were tetrahedral, spherical and square, with particle sizes ranging from 100 nm to 1 um.9) The detailed morphology of AgCl/Ag3PO4/diatomite was examined from Fig. 3(d), AgCl/Ag3PO4 particles were dispersed on the surface of diatomite. Among them, Ag3PO4 particles still maintained the shape of tetrahedron and square, and AgCl nanoparticles were well dispersed on the surface of Ag3PO4. The surface of AgCl/Ag3PO4 is also very rough, which could also increase the surface area of the reaction system and had better photocatalytic performance.31) Moreover, the SEM element mapping of AgCl/Ag3PO4/diatomite in Fig. 4 indicated that Ag, Cl, P, O, and Si elements were uniformly distributed, which implied formation of AgCl, Ag3PO4, and diatomite composites. More detailed structure information was further studied by TEM and confirmed the analytical results of SEM.

    3.1.4 TEM analysis

    TEM images of diatomite, AgCl/Ag3PO4 and AgCl/ Ag3PO4/diatomite composite with different magnifications were shown in Fig. 5(a-c), respectively. It could be seen from Fig. 5(a) that the diatomite had a porous structure. Such a porous structure could actively adsorb dye molecules in a solution, providing a good platform for degradation reactions. It could be seen from Fig. 5(b) that there were many small AgCl particles on the surface of the Ag3PO4 particles, indicating that Cl− have successfully replaced PO43−, and AgCl particles had been formed to adhere to the surface of Ag3PO4. From Fig. 5(c), it could be definitely observed that the AgCl/ Ag3PO4 particles adhere tightly to the diatomite, and a small amount of particles adhere to the pores of the diatomite. This indicates that AgCl/Ag3PO4/diatomite composites have been successfully prepared.

    3.1.5 UV-Vis analysis

    UV-Vis-DRS was used to study the optical absorption characteristics of the prepared materials. As shown in Fig. 6(a), compared to pure AgCl, Ag3PO4 and composites, diatomite exhibits the lowest light absorption capacity, which may be attributed to the light scattering effect derived from the composition and structure of natural minerals.28) For pure Ag3PO4 particles, the visible light absorption boundary was 545 nm. After recombination with AgCl, the visible light absorption boundary was enlarged to 552 nm, and a slight red shift phenomenon occurred.31,33) With the addition of diatomite, the visible light absorption intensity of the composite material decreased to some extent. This may be the diatomite was added, many AgCl/Ag3PO4 particles adhered to the surface of the diatomite, resulting in a decrease in active ingredients30) which was consistent with XRD, SEM characterization results. The band gap energy of a semiconductor can be calculated by the following formula:

    αhv = A ( hv - E g ) n/2
    (1)

    where α, h, v, A and Eg is the absorption coefficient, the Plank constant, light frequency, a constant, and the band gap, respectively. The value of n depends on whether the transition is direct (n=1) or indirect (n=4) discrete photon in a semiconductor. According to formula (1), the forbidden band width of the sample is calculated by the (αhv)2-hv curve [Fig. 6(b)]. the band gap (Eg) values of AgCl, Ag3PO4 and AgCl/Ag3PO4/diatomite composite are estimated to be 3.12, 2.35, and 2.30 eV, respectively. Based on the previous study, the ECB and EVB of the catalysts can be calculated using the following equations:

    E VB  = X - E e  + 0 .5E g
    (2)

    E CB  = E VB  - E g
    (3)

    where X is the electronegativity of the semiconductor, which is the geometric mean of the electronegativity of the constituent atoms (5.95 eV and 6.04 eV for Ag3PO438) and AgCl39), respectively). Ee is the potential energy of the free electrons at a normal hydrogen electrode, which is 4.5 eV in here.40) According to formula (2) and (3), ECB and EVB for Ag3PO4 is 0.28 eV and 2.63 eV, respectively. ECB and EVB for AgCl is -0.02 eV and 3.10 eV, respectively.

    3.2 Photocatalytic performance under visible light

    The photocatalytic activity was subsequently investigated by the degradation of 20 mg/L RhB aqueous solution under visible light. Fig. 7(a) showed the change in the RhB concentration (C/C0) as a function of irradiation time under different photocatalysts, which were adsorbed for 30 min under dark conditions to achieve an adsorptiondesorption balance before visible light irradiation. As shown in Fig. 7(a), the dark adsorption process basically had little effect on the dye concentration. RhB dyes were not degraded in the absence of catalyst for 15 min. When AgCl/Ag3PO4/diatomite composite photocatalyst was added to the dye solution, the degradation degree of RhB dye could reach almost 100 % after 15 min, while the degradation efficiency of AgCl and Ag3PO4 was 33 % and 95 %, respectively.

    To disclose the photocatalytic performance in detail, the pseudo first-order kinetic model was employed, and the corresponding rate constants (Kapp) could be calculated by following equation:

    -ln(C t /C 0 ) = K app t
    (4)

    where Ct, Co, Kapp and t represent the RhB concentration at time of t and zero, react constant and irradiation time, respectively. According to the calculation simulation of formula (4), as shown in Fig.7(b), it's indicated that the photodegradation kinetics curves of RhB in the precence of as-prepared samples follow the pseudo first-order reaction kinetic model. It could be clearly seen that the rate constant of the AgCl/Ag3PO4/diatomite composite is 0.2587 min−1, which is 1.36 times and 9.6 times higher than that of pure Ag3PO4 and AgCl, respectively. Fig. 7(c) showed the absorption spectrum of RhB with different irradiation times in Ag3PO4 system. With the irradiation time increased, the absorption peak decreased obviously and the maximum absorption wavelength shifted to the left with a slight blue shift, which might account for the destruction of group RhB during degradation.41) Although the initial degradation efficiency of Ag3PO4 was high, its cycle stability is poor, which has dropped to about 40 % after five cycles. AgCl/Ag3PO4/diatomite could still maintain a very high activity after five cycles [Fig.7(d)].

    3.3 Possible photocatalytic mechanism of AgCl/ Ag3PO4/diatomite

    In order to investigate the main active species during the degradation process of phenol using the AgCl/Ag3PO4/ diatomite composite, the trapping experiments were carried out. The benzoquinone (BQ) was used as superoxide radical species (·O2) scavenger, and ethylenediamine tetra acetic acid disodium salt (Na2-EDTA) as the hole (h+) scavengers. Isopropanol (IPA) was employed as the scavengers of hydroxyl radical (-OH).1) As shown in Fig. 8, with the addition of Na2-EDTA and BQ, the degradation efficiency of RhB was significantly reduced, indicating that h+ and ·O2 were the main active materials in photocatalyic experiments. In contrast, the addition of IPA in the solution did not significantly affect the photocatalytic activity of the composite, indicating that ·OH was not the main active substance and had no significant effect on the degradation process.

    The relative positions of the energy bands of Ag3PO4 were separated by 2.35 eV, and the conduction band (CB) and valence band (VB) energy levels of Ag3PO4 were estimated to be 0.28 and 2.63 eV vs. NHE, respectively. Meanwhile, AgCl could not be excited under visible light due to its large band gap and the conduction band (CB) and valence band (VB) energy levels of AgCl were ca. -0.02 and 3.10 eV vs. NHE, respectively.21,32,42) In this case, the photo-excited electrons in the CB of Ag3PO4 and the photo-excited electrons in the CB of AgCl could not be captured by the adsorbed O2 to produce an ·O2 active material because the CB edge potential of Ag3PO4 (0.28 eV vs. NHE) and the CB edge potential of AgCl (-0.02 eV vs. NHE) was more correct than the one-electron reduction potential of oxygen (E0(O2/·O2 = -0.046 eV vs. NHE)).21,31) However, since AgCl/Ag3PO4 was a photosensitive semiconductor, elemental Ag particles were unavoidably reduced on the surface of the composite under visible light irradiation. A small amount of Ag nanoparticles formed in situ had a strong surface plasmon resonance effect, which could capture electrons on the AgCl surface to reduce O2 and generate ·O2.28,35) Based on the above results, a possible photocatalytic mechanism for AgCl/Ag3PO4/diatomite composites was proposed.

    A possible photogenerated and transfer process of electron-hole pairs was shown in Fig. 9. Under visible light irradiation, Ag3PO4 was excited by the conduction and valence bands of photo-generated electrons and holes, while AgCl could not be excited due to its wide band gap. Diatomite was mainly used as a carrier to provide a corresponding platform for the reaction, and it could also adsorb dye molecules in the solution to promote the reaction.26,37) The conduction band (CB) potentials of Ag3PO4 and AgCl were +0.28 and -0.02 eV, and the valence band (VB) potentials of Ag3PO4 and AgCl are +2.63 and +3.10 eV, respectively, relative to the ordinary hydrogen electrode (NHE) (Fig. 9).31,32,35) The photogenerated electrons generated by silver phosphate were transferred to the conduction band of AgCl, but because the conduction band potential of AgCl was -0.02 eV, O2 could not be oxidized to ·O2 (E0(O2/·O2 = -0.046 eV vs. NHE)), So a part of the photogenerated electrons combine with Ag+ in AgCl generated a small amount of simple Ag0.30) The generation of simple Ag0 caused the SPR resonance effect, which further enhanced the absorption effect of visible light and accepted photogenerated electrons from the conduction band of AgCl Combines with dissolved oxygen in the solution generating ·O2.28,43) The generated ·O2 reacted with the dye molecules adsorbed on the diatomite and degraded them into CO2 and H2O. When the photo-generated electrons on the Ag3PO4 conduction band were transferred to the conduction band of AgCl, their photo-generated holes h+ remain in the valence band, and they were bound to the RhB dye molecules adsorbed on the diatomite surface and dissolved in the solution, thereby its degradation.

    4. Conclusions

    In summary, a novel AgCl/Ag3PO4/diatomite composite has been successfully synthesized using the microemulsion method and anion in situ substitution method. The photocatalytic experimental results indicated that AgCl/ Ag3PO4/diatomite composites exhibited higher photocatalytic activity and good stability with negligible loss of activity after five cycles than pure Ag3PO4. The radical trap experiments showed that the degradation of RhB was mainly driven by the holes and ·O2 free radicals. The enhanced photocatalytic activity of this AgCl/Ag3PO4/ diatomite composite could be mainly attributed to highly efficient charge separation through the synergistic role of AgCl, Ag3PO4, diatomite and in situ photoreduced Ag nanoparticles. The synergistic effects of those factors resulted in the improvement of photocatalytic performance of the AgCl/Ag3PO4/diatomite composites. Furthermore, this work has provided some suggestions for sunlightdriven photocatalysts and the decoration industry.

    Acknowledgments

    This work were financially supported by Initial Scientific Research Fund of Anhui Jianzhu University (No. 2017QD14) and the 2014 Anhui Provincial Universities Excellent Young Talents Plan (No. gxyq64).

    Figure

    MRSK-30-8-383_F1.gif

    XRD patterns of as prepared diatomite (a), AgCl (b), Ag3PO4 (c), Ag3PO4/diatomite(d) and AgCl/Ag3PO4/diatomite(e) samples.

    MRSK-30-8-383_F2.gif

    XPS spectra of the AgCl/Ag3PO4/diatomite photocatalyst: (a) survey, (b) Ag 3d, (c) Cl 2p, (d) P 2p, (e) Si 2p and (f) O 1s.

    MRSK-30-8-383_F3.gif

    SEM images of (a) diatomite, (b) AgCl, (c) Ag3PO4 and (d)AgCl/Ag3PO4/diatomite

    MRSK-30-8-383_F4.gif

    SEM element mapping of prepared AgCl/Ag3PO4/diatomite composite for Ag, Cl, P, O and Si elements.

    MRSK-30-8-383_F5.gif

    TEM images of (a) diatomite, (b) AgCl/Ag3PO4 and (C) AgCl/Ag3PO4/diatomite, respectively.

    MRSK-30-8-383_F6.gif

    (a) UV-Vis-DRS spectra of diatomite, AgCl, AgCl/diatomite, Ag3PO4, Ag3PO4/diatomite, AgCl/Ag3PO4 and AgCl/Ag3PO4/diatomite, respectively and (b) the plot of (αhv)2 versus Eg for the band gap energy of AgCl/Ag3PO4/diatomite, Ag3PO4 and AgCl, respectively.

    MRSK-30-8-383_F7.gif

    (a) Photocatalytic degradation curves of RhB with different catalysts under visible light irradiation; (b) the kinetics plots over the as-prepared samples; (c) the UV-Vis absorption spectra of RhB in the presence of AgCl/ Ag3PO4/diatomite composite and (d) cycling runs of Ag3PO4 and AgCl/ Ag3PO4/diatomite for the degradation of RhB.

    MRSK-30-8-383_F8.gif

    Trapping experiment of the active species in AgCl/Ag3PO4/ diatomite system for RhB degradation under the visible light irradiation.

    MRSK-30-8-383_F9.gif

    Roposed photocatalytic mechanism over the AgCl/Ag3PO4/ diatomite composite.

    Table

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