Preparation And Photocatalytic Property Of Bismuth Oxyhalide-based Composite Nanofibers

Semiconductor materials as photocatalyst hold great prospects for renewable energy substitutes and environmental protection. Nanostructured BiOX（X=Cl, Br, I） with favorable features of unique layered crystal structure and suitable band gaps has been demonstrated to be a promising photocatalytic material. However, the nanostructured BiOX is still far from practical applications due to its following draw backs. Firstly, the rapid recombination of photo-generated carriers of Bi OX will induce low quantum efficiency. Secondly, the nanostructural BiOX are always in powder form, the agglomeration of which will reduce the accessible surface areas as well as the photocatalytic efficiency. Thirdly, the difficult separation of BiOX from the reaction system will cause the secondary pollution. In order to effectively overcome these disadvantages, we have fabricated a series of one-dimensional heterostructurecomposite photocatalysts based on BiOX through electrospinning technique,hydrothermal method and successive ionic layer adsorption and reaction（SILAR）.（1） Heterostructures of p-type BiOX（X=Cl, Br, I）/n-type TiO₂ nanofibers（p-BiOX/n-TiO₂ NFs） were prepared successfully by combining the electrospinning technique, solvothermal method and SILAR. As a result, BiOX nanosheets with high exposed ratio of {001} facets dispersed uniformly on TiO₂ nanofibers. The obtained p-BiOX/n-TiO₂ NFs with the advantages of p-n heterojunctions have exhibited enhanced photocatalytic activity. Due to the different valence band potentials, the as-prepared p-BiOBr/n-TiO₂ NFs exhibited higher UV-light photocatalytic activity than that of p-BiOCl/n-TiO₂ NFs, while p-BiOIr/n-TiO₂ NFs showed enhanced visible light photocatalytic activity. Moreover, the p-BiOX/n-TiO₂ NFs with three-dimensional nonwoven web structurecould be separated and recycled easily by sedimentation.（2） Using electrospun carbon nanofibers（CNFs） as templates, BiOI nanosheets/carbon nanofibers heterostructures（BiOI/CNFs） have been successfully obtained via SILAR. As expected, the BiOI/CNFs have presented a much higher degradation rate than that of the pure Bi OI under visible light. The enhanced photocatalytic activity could be attributed to that the conductive CNFs as substrate could effectively improve the separation and transformation of photogenerated charges. Moreover, the fabricated BiOI/CNFs could be easily recycled without a decrease of the photocatalytic activity due to their ultra-long one-dimensional nanostructural property.（3） BiOI nanosheets were successfully immobilized on electrospunpolyacrylonitrile（PAN） nanofibers through SILAR at room temperature. By adjusting the SILARcirculations, the BiOI content on the prepared Bi OI/PAN nanofibers（BiOI/PAN NFs） could be facilely controlled. Due to the high photocatalytic activity of BiOI nanosheets as well as the high surface area of nanofibrous structure, the BiOI/PAN NFs showed outstanding visible-light photocatalytic activity for degradation of both Rhodamine B and Methyl orange. Moreover, the improved photocatalytic activity has been achieved with increasing the content of BiOI in the composites. It was also worth noting that the BiOI/PAN NFs could be reused almost without decrease of photocatalytic activity after three recycling,which could be ascribed to the large aspect ratio and self-supporting flexibility of the obtained BiOI/PAN NFs.