Bismuth-based Photocatalyst: Structure And Photocatalytic Performances

As environmental and energy issues become more and more important,How to rationally utilize light energy is an effective way for people to solve environmental and energy problems.As a means of rational use of light energy,photocatalytic technology not only saves energy and protects the environment,but also has the advantages of high degradation efficiency of pollutants and green organic conversion routes.In the description of this article,it is mainly applied to incomplete benzyl alcohol molecules,As one of the simplest aromatic alcohols,benzyl alcohol small molecules have a paralytic nerve effect and are harmful to eyes,respiratory tract,and skin.On the other hand,carbonyl compounds,as oxidation products of hydroxyl group,are not only intermediates of some drugs and spices,but also play an indispensable role in many important organic synthesis.Bi₂WO₆ is one of the most commonly used photocatalysts,and as a semiconductor material with the right band width and one of the stable photocatalysts,However,its shortcomings are low quantum utilization rate and high recombination rate of photogenerated electrons and holes,so that the photocatalytic performance is not ideal.Based on the above shortcomings,improving the performance of semiconductor photocatalyst is one of the goals of future research,and the second is to build and research new semiconductor photocatalysts.There are three common modification methods for semiconductor photocatalysts:the first method is supported catalyst（such as supported Pt and Au）,the second method is doped（such as P and W）,and the third method is to form heterojunction structure.The first three methods are based on the modification of the original catalyst,but the effect on the inherent characteristics and disadvantages of the photocatalyst（such as too wide band gap）will be greatly reduced.Therefore,the research and preparation of novel photocatalyst is the first problem.In the first part of this paper,nano-flower-like Bi₂WO₆ was prepared by hydrothermal reaction.The precursor of bismuth element is bismuth nitrate,and the precursor of tungsten element is sodium tungstate.The activity test showed that the conversion rate of pure bismuth tungstate for photocatalytic selective oxidation of benzyl alcohol was only 58%.The effect was not ideal.Therefore,we intend to improve the photocatalytic performance of bismuth tungstate nanocrystalline sheet by modifying bismuth tungstate nanocrystalline sheet from two aspects:bismuth quantum dot and oxygen vacancy.bismuth quantum dot was formed by using different concentration of sodium borohydride as reducing agent.On the other hand,considering that scientists have studied more oxygen vacancies in recent years,this article also designs and manufactures surface oxygen vacancies.Since surface oxygen vacancies are particularly important for photocatalytic reactions,their effects are mainly reflected in two aspects:firstly,the surface oxygen vacancies can increase the unevenness of the catalyst surface,which increases the contact between the catalyst molecules and the substrate.On the other hand,surface oxygen vacancies can act as acceptors of electrons,which can improve the separation efficiency of photo-generated electrons and holes and reduce photo-generation.Electron and hole recombination.The macro performance is to greatly improve the photocatalytic performance.Based on the advantages of the above oxygen vacancies,we reduced the bismuth tungstate nanosheets under oxygen-free conditions,thereby forming bismuth tungstate nanosheets modified with bismuth quantum dots and oxygen vacancies.Among them,2.5BWO showed the highest activity.There are several reasons for its highest reactivity:first,the increase in specific surface area increases the contact area between the photocatalyst and the substrate;second,the bismuth quantum dots and oxygen vacancies greatly increase the absorption of visible light by the photocatalyst ability;third,bismuth quantum dots and oxygen vacancies can be used as electron acceptors,thereby reducing the recombination of photogenerated electrons and holes,thereby increasing the separation efficiency of photogenerated electrons and holes;fourth,oxygen vacancies can also be used as reactive center,thereby improving photocatalytic performance.Bismuth-based photocatalyst was synthesized by simple hydrothermal reaction in this paper.At the same time,it is modified by in-situ reduction.Meanwhile,the structure and morphology were proved by XRD,FESEM,HRTEM,BET,FTIR,XPS,etc.Moreover,GC2014C（Shimadzu）was used to test the photocatalytic performance of a 300W xenon lamp under the condition of wavelength greater than 400.According to the oxidation efficiency of aromatic alcohol small molecules,2.5 BWO group of photocatalysts had the best performance.