First Principles Study,Preparation And Photocatalytic Performance Of G-C₃N₄/β-Bi₂O₃ Photocatalyst

Semiconductor photocatalytic technology,which can use solar energy to degrade organic pollutants and prepare H2,CH4 and other chemical energy,has become one of the new technologies with the most potential to solve energy crisis and environmental pollution.Among them,the construction of semiconductor heterostructure plays an important role in improving carrier transport and photocatalytic efficiency.At present,the study of photocatalytic semiconductor heterojunction types including type-II and Z-scheme two kinds.Among them,Z-scheme semiconductor heterojunction has attracted much attention because its electrons are enriched in the conduction band with higher reduction ability and holes are enriched in the valence band with higher oxidation ability during the photocatalytic process,which fully explores the redox ability of semiconductors.Now,for g-C3N4/β-Bi2O3 heterojunction exploration,most concentrated in improving light catalytic properties.Among type-Ⅱ and Z-scheme conversion mechanism,the formation of the heterojunction and photocatalytic performance,the relationship is still are unclear.In this paper,g-C3N4/β-Bi2O3 heterojunction is selected as the research object.By introducing defects into g-C3N4 and β-Bi2O3 semiconductor,the influence law of defects on the band structure and the type of heterojunction is explored,so as to achieve the optimization of the photocatalytic performance of heterojunctions and realize the controlled preparation of Z-scheme heterojunctionThe first principle method is used to theoretically clarify that the introduction of oxygen vacancy can introduce the acceptor defect level at the top of the β-Bi2O3 valence band and reduce the band gap,and the variation value of the band gap increases with the increase of doping concentration in a certain range of concentration.A series of β-Bi2O3-x with different concentrations of oxygen vacancies are prepared experimentally.The results show that the heating rate of 8℃/min has the most obvious influence on the light absorption performance,which is conducive to the introduction of oxygen vacancy.The band gap of β-Bi2O3(5/6)is the smallest and the photocatalytic performance is the bestThe first principle calculation method is used to theoretically show that the introduction of nitrogen vacancy can introduce the accept-defect energy level at the top of its valence band and reduce the band gap of g-C3N4.The introduction of nitrogen vacancy will reduce its work function and realize the Fermi energy level moving up.A series of g-C3N4-y with different nitrogen vacancy concentrations are prepared through experiments.DRS and Tauc curves indicating that the introduction of nitrogen vacancy can effectively improve the energy band structure of materials,and the light absorption performance changes with the concentration of nitrogen vacancy,which is conducive to the improvement of photocatalytic performanceUsing the first principle calculation method,to calculate the g-C3N4/β-Bi2O3 heterojunction band and charge transfer character stics,the results show that it is typical type-Ⅱ heterojunction.And by introducing nitrogen vacancy in g-C3N4,adjusting the g-C3N4 Fermi level relative to the β-Bi2O3,can achieve type-Ⅱ heterojunction to Z-scheme g-C3N4/β-Bi2O3 heterojunction controllable transformation.In addition,a series of g-C3N4/β-Bi2O3-x heterojunctions are prepared.Compared with β-Bi2O3-x,the photocatalytic performance is improved by 8 times.