Study On Surface Regulation Technology And Photocatalytic Properties Of Tungsten Oxide

As a characteristic semiconductor photocatalyst,tungsten trioxide（WO₃）has attracted more and more attention due to its easy availability of raw materials,non-toxicity,wide response range of solar spectrum,and stability of physicochemical properties.However,at present,using WO₃ alone as a photocatalyst has low quantum efficiency and high recombination rate of photo-generated carrier,resulting in its photocatalytic activity still lower than expected.For this reason,researchers have done a lot of research to boost the quantum efficiency and increasing the separation efficiency of photo-generated carrier.Research results have proved that by adjusting the surface of WO₃,such as the formation of heterojunction or homojunction on the surface of WO₃ using two different susbstance with different energy band structure,can significantly improve the separation efficiency of photogenerated carriers,which can further improve the photocatalytic activity.Therefore,it has important significance to regulate the surface of tungsten trioxide photocatalyst.In this paper,highly active WO₃-based photocatalysts were prepared through constructing heterojunction and homojunction on the surface of WO₃.In this paper,rod-like hexagonal tungsten trioxide（h-WO₃）was synthesized by hydrothermal method,and then calcined at different temperatures to obtain a series of samples with different surface structures.The results of XRD and UV-raman demonstrated that the phase transition process on the surface of h-WO₃ had obvious"hysteresis"effect compared with that of bulk phase,which proved that the phase transition of h-WO₃started from bulk phase and then gradually diffused to the surface.HRTEM analysis result further proved that the phase transition from h-WO₃ to m-WO₃firstly occured in bulk phase,then diffused to the surface.With further increasing the calcination temperature,T-Na₂W₄O₁₃ was formed on the surface and finally T-Na₅W₁₄O₄₄ was obtained.XPS analysis result confirmed that the Na:W on the surface of samples increased gradually with the increase of calcination temperature which proved that Na⁺gradually diffused to the surface during calcination process and finally induced the formation of T-Na₂W₄O₁₃ and T-Na₅W₁₄O₄₄.The order of oxygen evolution using different samples under visible light was that:h-WO₃-500-2h>h-WO₃-470-2h>h-WO₃-450-2h>h-WO₃-600-2h>h-WO₃>h-WO₃>h-WO₃-700-2h>h-WO₃-800-2h,wh-ich was in consistent with the order of SPV signal intensity.This can proved that the increase of oxygen evolution activity of different samples was due to the improvement of photogenerated carrier separation efficiency.In addition,we used h-WO₃ as a carrier,followed by second hydrothermal treatment using sodium tungstate as m-WO₃ precursor to obtain a series of n%m/h-WO₃ samples.The XRD and SEM results showed that a surface heterojunction was formed on the surface of h-WO₃ through the uniform decoration of m-WO₃ when the loading amount of m-WO₃ was low.With further increasing the loading amount to 10%and 20%,independent bulk m-WO₃ was formed,and no effective contact surface was formed between m-WO₃ and h-WO₃.The degradation experiment indicated that photocatalytic RhB degradation activity of surface homojunction samples were higher than that of pure m-WO₃ and h-WO₃.The specific activity order was that:5%m/h-WO₃>3%m/h-WO₃>10%m/h-WO₃>20%m/h-WO₃>1%m/h-WO₃>m-WO₃>h-WO₃,the SPV signal intensity order was in consistent with the photocatalytic activity order,which proved that the boosted photocatalytic activity after surface modification was due to the increase of photo-generated carrier separation efficiency.Active trapping experiments results demonstrated that·O₂^-,h⁺,and·OH all participated in the RhB degradation reaction,but·O₂^-and·OH played a leading role in the reaction.In this chapter,it was found that the modification of m-WO₃/h-WO₃homojunction on the surface of h-WO₃ can significantly improve the photocatalytic activity.