Study On The Synthesis And Photocatalytic Performance Of G-C₃N₄/BiVO₄ Composite Photocatalysts

In resent years, the novel metal-free material, graphite carbon nitride (g-C3N4) as a semiconductor photocatalyst, has attracted public intense interest. It displays the photocatalytic activity under visible light with the band gap about 2.7 eV. Nevertheless, the high recombination rate of photo-generated electron-hole pairs is a main issue limiting the significant photocatalytic efficiency of g-C3N4. Therefore, some other semiconductors could be used to construct the suitable matched g-C3N4-based heterojunction to improve the charge separation efficiency and then enhance the quantum efficiency of g-C3N4. Based on the theory, the g-C3N4/BiVO4 heterojunctions were prepared by different methods, and the structure, morphology, photoelectric properties and photocatalytic performance were characterized and analyzed, and were respectively tested and discussed in liquid-solid and gas-liguid-solid systems.Novel visible-light-driven g-C3N4/BiVO4 composite photocatalysts were fabricated via sol-gel and simple mixing and heating methods. The photoactivity of the samples was evaluated by the decoloration of RhB under VL irradiation. The photocatalysts with different mass ratios of g-C3N4 and BiVO4 and calcination temperatures were characterized by XRD, TG, FT-IR, TEM, BET, XPS, DRS and PL spectra. The g-C3N4/BiVO4 heterojunction at a weight ratio of 80% calcined at 500℃ exhibited the most excellent photocatalytic ability for RhB decolorization under visible-light irradiation (λ>420 nm). It is attributed to the high adsorption activity and efficient charge separation of photoinduced charge carriers. The main reactive roles significantly contributed to the decolorization of RhB are holes, ·O2- and ·OH. Furthermore, the mechanism of the photodecolorization of RhB over g-C3N4/BiVO4 heterojunctions was also discussed.The visible light active BiVO4 coated on g-C3N4 sheets composite catalysts were synthesized via facile ultrasonic dispersion and calcination methods and used in the study for photocatalytic oxidation of NO in gas phase. The structure feature, morphology characteristics, visible light absorption capacity and photoelectronic properties were analyzed by XRD, FT-IR, XPS, TEM, PL, I-t and EIS characterizations. TEM results showed that the g-C3N4 after ultrasonic treatment was exfoliated into sheet structures and made BiVO4 uniformly dispersed on the g-C3N4 sheets. The activity test showed that when the mass ratios of g-C3N4 and BiVO4 is 1:1, the photoactivity reached the highest. It is also showed that NO was removed in the oxidation formation of NO2- and NO3-. The high photocatalytic oxidation of NO is attributed to the the suitable matched energy levels, which induced to the electron-hole seperation and high photogenerated carriers life. Thus the separated electron and holke were able to react with the external material to improve the photocatalytic activity.