Photocatalytic Property Enhancement For Composite Oxide By Nanostructure Fabrication And Anion Substitution

Developing novel photocatalysts with high energy efficiency and high activity isvery important for photocatalytic research. In our work, composite metal oxidenanocrystals with tailored shape and composite metal oxide by anion substitution wereadopted to realize this aim. Nanostructured photocatalysts usually have highphotocatalytic activities because of their special morphologies, high surface areas andhigh efficiency of electron-hole separation. And from the viewpoint of solar energyutilization, one effective way to narrow the band gap of photocatalyst is to elevate thevalence band of photocatalysts into a more negative position by anion substitution.Zn₃V₂O₇(OH)₂(H₂O)₂nanocrystals with various morphologies were successfullysynthesized by a template-free hydrothermal route. Significantly, this is the first timethat Zn₃V₂O₇(OH)₂(H₂O)₂was used as a photocatalyst for organic pollutant degradationunder UV light irradiation. It was found methylene blue could be fully degraded byfloriated like nanostructures of Zn₃V₂O₇(OH)₂(H₂O)₂less than80min. Moreover,Zn3V2O8with porous floriated like nanostructures could be formed via calcination ofthe corresponding Zn₃V₂O₇(OH)₂(H₂O)₂. The reaction constant of the best qualityZn3V2O8nanostructure was three time that of the sample prepared by solid-statereaction under visible-light irradiation.ZnWO₄photocatalysts with various morphologies could also be successfullysynthesized by a template-free hydrothermal route. The morphologies had a significantinfluence on the photocatalytic activity. ZnWO₄nanorods with maximal aspect ratioexhibited the highest photocatalytic activity among all the samples, methylene bluecould be degraded less than50min under UV light irradiation. This ZnWO₄nanorodsgrew preferentially along the [100] direction, and the two planes along the [100]direction—(010) and (011) planes could be speculate to be more active forphotodegradation.F^-substituted Bi₂WO₆(Bi₂WO₆-XFX) photocatalysts with high activity could besynthesized by reflux method. F-substitution could change the original coordinationaround the W and Bi atoms. Comparing with Bi₂WO₆, the photocatalytic activity ofBi₂WO₆-XFXincreased about1.5times for degradation of MB under visible-light irradiation. Density functional calculations and experiment revealed that the highactivities of Bi₂WO₆-XFXphotocatalysts come from its special band structure whichincrease the mobility of photoexcited charge carriers and possess a stronger oxidationpower.S^2-substituted Bi2MoO6(Bi2MoS2O4) photocatalysts with high energy efficiencycould be synthesized by reflux method. The visible-light response of Bi₂MoS₂O₄couldextend from470to630nm compared with Bi₂MoO₆. Moreover, Bi₂MoS₂O₄possessexcellent photocatalytic activities in the broad range under visible light. Densityfunctional calculation revealed that Bi₂MoS₂O₄had narrower band gap compared withBi2MoO6because S3p orbital contributed to the valence band formation. Furthermore,this reflux method could afford guidance for designing and synthesizing the other anionsubstitution photocatalysts.