Study On The Synthesis Of C₃N₄-BiVO₄ Photocatalyst And Its Photocatalytic Activity Driven By Visible Light Irradiation

At present, using visible light for the photodegradation of pollution is a new way to solvethe problems of the global energy crisis and environmental pollution. To develop new photocatalysts with high efficiency and to broaden photoresponse range of the photocatalysts have become challenging topics in the environmental photocatalytic field.Recent study has found that graphitis carbon nitride(C3N4) and bismuth vanadate(BiVO4) are novel visble-light-driven semiconductor due to their narrow band gap. Nevertheless, the hign recombination rate of photo-generated electron-hole pairs is a main issue limiting the significant photocatalyytic efficiency of C3N4 and BiVO4. Therefore, compositing C3N4 and BiVO4 improve the charge separation efficiency and then enhance the quantum efficiency. We composited two kinds of catalyst, with methyl orange as probe pollutants, studying the effect of compound method to its photocatalytic activity.This paper mainly includes the following aspects:(1) C3N4-BiVO4 compound photocatalyst has been successfully synthesized by C3N4 and BiVO4 precursor through hydrothermal process. The prepared photocatalysts were characterized by XRD, SEM, TEM, UV-vis DRS and BET surface area analysis. Using methyl orange as probe pollutants, in visible light degradation of methyl orange experiments, the optimum synthesis condition of C3N4-BiVO4 was selected as:m(C3N4)/m(BiVO4)=1:0.15, the pH value of hydrothermal precursor=6.0, hydrothermal synthetic temperature=180℃, hydrothermal holding time=6 h. After visible-light illumination for 5 hour, the decolorization rate of 20 mg/L methyl orange solution can amount to 97.42%, compared with pure C3N4 photocatalytic activity increased by 24.35%, compared with pure BiVO4 photocatalytic activity increased by 30.33%.(2) Using C3N4-BiVO4 compound catalyst at the optimal synthetic conditions for photocatalytic degradation of methyl orange experiments, results showed that the photocatalyst has the fastest degradation rate of methyl orange solution under the condition of partial acid, the highest decolorization rate; Adding H2O2 can promote the degradation of methyl orange; NaCl and Na2SO4 all can inhibit the degradation of methyl orange, and the similar degree of two kinds of salt restrain; Repeated use experiments show that C3N4-BiVO4 photocatalyst can be used repeatedly.(3) In the degradation of methylene blue and nitrophenol, C3N4-BiVO4 visible-light photocatalytic propertieshave been further investigated. After visible-light illumination for 3 hour,20 mg/L methylene blue decolorization rate can reach 98.87%; After visible-light illumination for 6 hour, decolorization rate of 10 mg/L nitrophenol can reach 97.31%; Results showed the excellent photocatalytic activity of C3N4-BiVO4.(4) Photocatalytic degradation of methyl orange, methylene blue and nitrophenol accord with pseudo-first-order reaction kinetics equation.This topic research will further widen the carbon nitride and vanadate photocatalyst research field, and the research result has a certain theories guide and realistic meaning to the treatment of dye wastewater and other refractory organic pollutants.