Preparation And Photoelectrochemical Performance Of Nanoscale BiFeO₃ And Hydrogen-treated BiFeO₃

Semiconductor photocatalytic technology has attracted much attention for many years, because it supplied an ideal way of energy ultilization and environmental treatment. As a traditional photocatalyst material, TiO2 is believed to be the most promising photocatalysts for its advantages such as high photocatalytic activity, low cost, environmently friendly, chemical stability and photocorrosion resistance et al. Unfortunately, owing to its wide electronic bandgap, TiO2 absorbs only the ultraviolet fraction of the solar spectrum, which accounts for just 5% of the solar irradiation. Therefore, development of photocatalysts activated by visible light would have a profound impact and would lead to many applications of practical relevance to society. BiFeO3 is a well-known multiferroic material that exhibits spontaneous magnetic and ferroelectric properties at room temperature, since it potentially offer a winde range of applications in information storage process, spintronics and multiple-state memories. In addition, BiFeO3 has also been recognized as a visible light-driven photocatalysts because of its narrow band gap.In this dissertation, we focus on sample preparation at first. We have prepared a nanoscale, high performance rhombohedral perovskite BiFeO3 photocatalyst using a simple and effective method. Then hydrogen treatment was employed to modify Bi FeO3 nanoparticle. There are two main parts in this thesis:In the first part of this thesis, BiFeO3 nanoparticles with different grain size were synthesized via solvent evaporation method. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, Raman spectra and UV-visible diffuse reflectance spectra. Photoelectrochemical performance was further examined. It was found that the growth parameters, such as annealing temperature and time, were importance to the photoelectrochemical properties of BiFeO3 nanoparticles.In the second part of this thesis, hydrogen treatment was employed to modify Bi Fe O3 nanoparticle. Hydrogen-treated Bi FeO3 nanoparticles with different hydrogenation degrees were efficiently synthesized through annealing pristine BiFeO3 in hydrogen atmosphere for different time. Compared with pristine BiFeO3, the hydrogen-treated BiFeO3 exhibited enhanced photoelectrochemical performance and photocatalysis activity. The sample prepared at 300? for 15 min exhibited the highest photocurrent density and optimal photoelectrochemical performance. Such enhanced photoelectrochemical performance could be ascribed to the narrowed band gap and increased donor density as a result of formation of oxygen vacancies; while the highly concentrated defects in BiFeO3 act as charge annihilation centers and most of the photogenerated carriers are consumed through significantly enhanced non-radiative recombination, which strongly inhibits the photoactivity of BiFeO3.