Study On Visible Light Photocatalytic Degradation Performance Of TiO₂/BiOX Reinforced By Dendritic Nanofiber

Photocatalytic oxidation technology has attracted much attention in the treatment of dye wastewater due to its low cost and high oxidation capacity.As the common semiconductor photocatalysts with excellent performance,titanium dioxide（TiO₂）and bismuth halide oxide（BiOX,X=I,Br,Cl）have received tremendous interests,but they still suffer from the low solar light utilization,easy agglomeration and difficulty in recycling,limiting their practical applications in the treatment of dye wastewater.To alleviate these constrains,a tree-like polyvinylidene fluoride（PVDF）nanofibrous membrane prepared by electrospinning was employed as support for TiO₂and TiO₂/BiOI heterojunctions,respectively,to construct highly efficient photocatalytic systems in this paper.In addition,by using amidoximated polyacrylonitrile fiber（AO-PAN）as the support,a fibrous photocatalyst with Fe doped bismuth halide oxide solid solution(Fe-BiOCl_xI_1-x)was also prepared via a one-step solvothermal in-situ synthesis method.The as-prepared fibrous photocatalysts were characterized and analyzed using various techniques,and then their photocatalytic performance was evaluated in the dye degradation.The photocatalytic mechanism of these catalytic systems was also explored.The results showed that the tree-like PVDF nanofibrous membrane consisted of a backbone fiber with an average diameter of 310 nm and branching fibers with diameters ranging from 5-100 nm,and TiO₂ could be uniformly distributed on the surface of the backbone and branching fibers.Compared with conventional PVDF nanofibrous membranes loaded with TiO₂ photocatalysts,the tree-like nanofibrous membrane showed higher hydrophilicity and specific surface area,which increased the equilibrium adsorption of dyes in water by 6.4 times;it also showed better photocatalytic performance,resulting in 2.0 and 3.3 fold higher degradation rate constants under UV and visible light irradiation,respectively.The high specific surface area of tree-like nanofibers provided more loading sites for further growth of BiOI,which enabled the successful construction of TiO₂/BiOI heterojunctions,and the introduction of BiOI significantly enhanced their visible light response.The high specific surface area of the tree-likenanofibrous membrane promoted the adsorption of dye molecules and the photogenerated charge separation at the interface of the heterostructure,so that the optimal composite photocatalyst exhibited 3.2 and 3.6 fold higher visible light driven photoactivity than the fibrous photocatalysts loaded with TiO₂ and BiOI alone,respectively.This composite photocatalyst also exhibited excellent recycling performance.In addition,Fe ions could act as a bridge to firmly anchor the bismuth halide oxide(BiOCl_xI_1-x)onto AO-PAN through its strong coordination interaction with amidoxime groups.Meanwhile,the coordination bonding between the fiber ligand and Fe ions can not only enhance the visible light response of the photocatalyst through LMCT effect,but also promote the charge separation at the photocatalytic reaction interface,leading to a high photocatalytic activity that the completely dye degradation could be achieved within 60 min visible light illumination.