Study On Preparation, Modification And Photocatalytic Performance Of BiVO₄ Photocatalyst

Semiconductor photocatalysis technology is one of the best means to solve the current global energy crisis and environmental pollution.Because of its efficiency and cleanliness,ease of implementation and high selectivity,it has a wide range of applications in the catalytic environmental protection industry,such as obtaining clean energy,eliminating harmful pollutants and solving the greenhouse effect,etc.However,sunlight as an energy source has a low utilization rate,so how to choose an efficient and pollution-free photocatalyst is the core problem of photocatalytic technology.As a visible light semiconductor catalyst,bismuth vanadate（BiVO₄）has been widely studied due to its nontoxicity,suitable band gap and high loading efficiency.However,the reported BiVO₄ materials generally suffer from the problem of easy recombination of internal electrons and holes,resulting in low quantum efficiency and limited photocatalytic activity.The preparation of BiVO₄ photocatalytic materials by various modification methods to effectively improve the photocatalytic performance has been reported,but the research methods are generally single and complex.In this paper,starting from the morphology regulation,element doping and structural recombination of BiVO₄,a low-temperature synthesis method is used to inhibit the crystal phase transition of BiVO₄,doping to form a solid solution to adjust the energy band structure and supply active sites,wide-narrow energy band coupling to form a heterojunction and the reliable film preparation process to improve the film quality of BiVO₄.The efficiency and stability of BiVO₄ photocatalyst were improved by the integrated and diversified regulation methods.The research contents of this paper are as follows:Chapter 1 describes the use of V₂O₅,Bi₂O₃ and TiO₂ to sinter BiTiVO₁₁ powder at high temperature.After ion exchange method,BiVO₄ two-dimensional nanosheets with quantum dot effect are exfoliated layer by layer with dilute nitric acid solvent.To explore its effect on the performance of the samples,gas chromatography oxygen production performance was used to evaluate the visible light photocatalytic performance of the prepared samples.The results show that BiV_0.98Ti_0.02O₄ nanosheets exhibit high photocatalytic activity for water oxidation under visible light irradiation,and the O₂ generation rate is 102.8μmol h^-1 g^-1,which is approximately 23 times higher than that of the undoped BiVO₄ sample.Chapter 2 innovatively adopts the in-situ hydrothermal assisted stirring method,using Bi（NO₃）₃·5H₂O and NH₄VO₃ as raw materials,and CH₄N₂S as a template to synthesize Bi₂S₃ nanowires and BiVO₄ nanoparticles heterojunction which are tightly connected and the connection is conducive to electron transport.Its photocatalytic performance is explored by decomposing Rhodamine B（RhB）to simulate the degradation of water pollution.The experimental results show that the performance of the stirred BiVO₄/Bi₂S₃ heterojunction is 2.2 times higher than that of the unstirred one,and 5.3 times higher than that of BiVO₄.The degradation efficiency can reach 75%under visible light irradiation.In addition,the catalyst has good stability because it still has good photocatalytic activity after 4 cycles.Chapter 3 solves the problem that BiVO₄ powder cannot be recycled,which makes it a source of pollutants,another problem is the doping amount of precursor is not easy to control and study in the preparation process of BiVO₄ powder.The pressed Mo-doped BiVO₄ target was glow-sputtered onto the fluorine-doped tin oxide（FTO）coated glass substrate by magnetron sputtering machine（PVD）.Deposition of nitrogen-doped Mo and N co-doped samples was studied by adjusting N₂ in sputtering atmosphere.After heating during sputtering and re-annealing in air,the thin-film samples showed good crystalline properties.It is found that the synergistic effect of Mo and N doping makes the samples exhibit higher photoelectric properties,and the Mo:BiVO₄ film has a better hydrogen production rate than the Mo-N:BiVO₄ film.