Preparation Of Silver Phosphate-based Composite Photocatalyst And Its Visible Light Photocatalytic Performance

In recent years,Semiconductor-based photocatalysis has received extensive attention and been widely applied in the removal of organic pollutants,due to its environmental friendliness,no secondary pollution and the effective utilization of abundant solar energy.However,most conventionally used semiconductor photocatalysts with larger band gap(such as TiO2,ZnO,etc.)exhibit excellent photocatalytic activity only under the UV-light irradiation(accounting for about 4%of solar spectrum),which greatly limit their practical applications.In 2010,silver phosphate(Ag3PO4),a visible-light-response photocatalyst with a relatively narrow band gap of 2.42 eV was reported.It can absorb light of wavelength less than 530 nm and has a quantum efficiency nearly 90%at 420 nm,and research has found that Ag3PO4 exhibits extremely high photocatalytic activity for O2 generation from water splitting as well as for the degradation of organic dyes under visible light irradiation.However,because silver phosphate is slightly soluble in aqueous solution,the free Ag+can be reduced to Ago by photo-exited electrons during the photocatalysis process,resulting in the photocorrosion of Ag3PO4,which would decrease the light absorption efficiency and the stability of Ag3PO4,meanwhile,severe agglomeration of Ag3PO4 leads to the relatively large particle size with smaller surface area.To date,many strategies have been explored to solve the above problems of Ag3PO4 photocatalyst.In this work,the photocatalytic activity and stability of Ag3PO4 can be improved through the following two aspects:on the one hand,Ag3PO4 is supported on the surface of diatomite with porous and disk-like shape structure.On the other hand,based on the matching energy band structure,according to the mechanism of Z-scheme electron transfer,Ag3PO4/RGO/Bi2MoO6 and magnetic PANI/Ag3PO4/NiFe2O4 composite photocatalysts are constructed.The main research contents are as follows:(1)A series of Ag3PO4/diatomite composite photocatalysts with different mass ratios are prepared by ultrasound-assisted precipitation method.The photocatalytic performance and stability of Ag3PO4/diatomite composites are investigated by the degradation of organic dyes under visible light irradiation.The composition,morphology,structure and optical properties of the as-prepared samples are characterized by XRD,FT-IR,SEM,TEM and XPS etc.The results show that the Ag3PO4 nanoparticles are uniformly dispersed on the surface of the diatomite;the obtained Ag3PO4/diatomite composites show enhanced photocatalytic performance for the degradation of acid brilliant scarlet dye compared with pure Ag3PO4 under visible light irradiation,and the 10%-Ag3PO4/diatomite composite exhibits the optimum photocatalytic degradation efficiency when the initial concentration of acid brilliant scarlet dye is 50mg/L with the pH 6 and the catalyst dosage is 1 g/L,which is approximately 3.6 times higher than that of pure Ag3PO4.Meanwhile,it shows the better stability after three cycles.(2)GO is obtained a modified Hunmers method,Ag3PO4/RGO/Bi2MoO6 ternary composite is synthesized by a precipitation-solvothermal method.The composition,morphology,structure,specific surface area and element state of the as-prepared samples are characterized by XRD,FT-IR,Raman,SEM,TEM,BET and XPS etc.The effects of GO and Ag3PO4 contents on the photocatalytic activity of composites are investigated by the degradation of methylene blue(MB).The results show that Bi2MoO6 flower-like microspheres are evenly dispersed on the layer of RGO,and Ag3PO4 nanoparticles are uniformly dispersed on the surface of RGO/Bi2MoO6 Compared with the pure Ag3PO4(0.435 m2/g),the specific surface area of Ag3PO4/RGO/Bi2MoO6(21.538 m2/g)is significantly increased.when the mass ratio of Ag3PO4,Bi2MoO6 and GO in the composite catalyst is 1.5:1:0.03,the degradation rate of MB is 97.53%,and its degradation rate(0.14575 min-1)was approximately 2.34,2.63 and 4.97 times faster than that of the Ag3PO4/Bi2MoO6 composite,pure Ag3PO4 and Bi2MoO6,respectively.Meanwhile,the Ag3PO4/RGO/Bi2MoO6 composite exhibited better stability compared with pure Ag3PO4 after four consecutive reuses.The separation and transmission efficiency of photogenerated electron-hole pairs for Ag3PO4/RGO/Bi2MoO6 composite are analyzed by PL,photocurrent and EIS.The conduction band and valence band positions of Ag3PO4 and Bi2MoO6 were calculated by UV-vis DRS spectrum and MS curve.Combined with free radical trapping experiments,the mechanism of Z-scheme charge transfer in the Ag3PO4/RGO/Bi2MoO6 composite was further confirmed,and RGO act as the a charge transmission bridge to accelerate the electron transfer from Ag3PO4 to Bi2MoO6.(3)NiFe2O4 is prepared by hydrothermal method,PANI/Ag3PO4/NiFe2O4 magnetic photocatalyst is prepared by in-situ precipitation method.The composition,morphology,structure and element state of the samples are investigated by various characterization methods.The effects of NiFe2O4 and PANI contents on the photocatalytic activity of composites are investigated by the degradation of Rhodamine B(RhB)and methyl orange(MO)dyes.The results show that when the mass ratio of PANI,Ag3PO4 and NiFe2O4 in the composite catalyst is 0.03:1:0.07,the degradation rates of RhB and MO are 100%and 94.97%,respectively,and their degradation rates are 12.1 and 15.4 times of Ag3PO4,respectively.Meanwhile,the PANI/Ag3PO4/NiFe2O4 composite displays excellent photocatalytic performance on the degradation of colorless organic pollutants(tetracycline hydrochloride,nitrobenzene and bisphenol A)under the visible light irradiation.The PANI/Ag3PO4/NiFe2O4 catalyst exhibits a superior stability than pure Ag3PO4 after three consecutive reuses.The results of free radical trapping experiments indicate that h+ and ·O2-are the main active species in the system.On the basis of PL and EIS spectra analysis results,it is known that the separation and transfer efficiency of photoinduced electron-hole pairs in the PANI/Ag3PO4/NiFe2O4 composite can be effectively improved by the introduction of PANI and NiFe2O4.The conduction band and valence band positions of PANI,Ag3PO4 and NiFe2O4were calculated by UV-vis DRS spectrum and MS curve.The mechanism of double Z-scheme charge transfer in the PANI/Ag3PO4/NiFe2O4 composite are proposed.