Enhanced Photocatalytic Performance Induced By Surface Oxygen Vacancy

In the work, surface oxygen-vacancies photocatalysts were fabricated by twomethods: vacuum deoxidation and controllable hydrogen reduction. The density ofstates (DOS) of the photocatalysts valence band (VB), can be regulated and controlledby the structure, number and the kind of surface oxygen vacancies, which can becontributed to the narrowed the band gap and the broaden the VB, thus promoting theseparation efficiency of photoinduced electron-hole pairs, and improving thephotocatalytic activity. In addition, the theory calculation indicates that the influence ofsurface oxygen-defect states on the band structure, the DOS of the VB, photoabsorptionperformance and oxidation-reduction potential for photocatalysts. A variety oftechnologies were utilized to reveal the physical structure of surface defects and bulkdefects, and to display the external relations of defect states with the photodegradationprocess and the photocurrent, and to imply the inherent law of defect states with theseparation and transfer of the photoinduced electrons. This work discovers thepromotion mechanism of surface oxygen vacancies on the separation of photoinducedelectron-hole pairs, thus new high activity photocatalysts were prepared successfully. Ina word, it is beneficial to further understand the relationship of surface oxygen defectswith the enhanced separation and transfer of photoinduced electrons, and it has apromoting role in the development of physics and chemistry.ZnO, BiPO4and Bi2WO6three kinds of typical semiconducting photocatalysts werechosen as the research objects. And it is systematically studied the law and mechanismof the enhanced photoactivity and the improved energy efficiency, which both wereinduced by surface oxygen-vacancy defect.Surface oxygen-vacancy ZnO was fabricated by two means-vacuum deoxidation andcontrollable hydrogen reduction. After surface oxygen vacancies were introduced on theZnO, the visible photoactivity and photocurrent are unambiguously generated, and theUV photocatalytic activity on methylene blue (MB) and photocurrent increase to about2.1and2.5times, respectively. In addition, the photodegradation mechanism has notchanged, the photoinduced holes is still the main active species. From the calculationresults based on the first-principle theory, it can be found that the small electronic DOS are produced on/in the top of the valence band maximum (VBM) due to the introductionof surface oxygen-defect states. Thus the VBM rises, which is contributed to thebroadened the VB width and the narrowed the band gap, so the UV activity increasesand the visible activity is produced.BiPO4photonanorods with surface oxygen vacancies were also prepared by thevacuum deoxidation and controllable hydrogen reduction means. The effects of thenumber and extent of oxygen vacancies, on the photocatalytic performance andphotoresponse wavelength range were investigated. The results show that onlycontrolled the surface oxygen vacancies to the maximum and hardly any bulk oxygenvacancies formed, the first-rank photoactivity can be possessed. Furthermore, throughthe four cycle degradation on MB, active-contrast experiment of surfaceoxygen-vacancy BiPO4before and after10months storage, and the degradation ondifferent types of organic pollutants, show that surface oxygen-vacancy BiPO4has agood stability and almost no selectivity on the decomposition of organic pollutants.Bi2WO6nanoplates with surface oxygen vacancies were synthesized via acontrollable hydrogen reduction way. The results show that the photoresponsewavelength range is expanded to600nm, which indicates that surface oxygen vacancyBi2WO6-xhas a preferable photoactivity over a wide range of visible light region.Additionally, the photocatalytic performance under simulated solar irradiation is clearlyhigher than that of under visible light, which suggests that the UV photoactivity is alsoimproved.