Tungsten-based Photocatalyst: Preparation And Photocatalytic Performances

Selective oxidation of alcohols to carbonyl compounds as one of the most important functional group transformations in industrial chemistry has received much attention,because carbonyl compounds such as aldehydes and ketones are widely used in fragrance,confectionary,and pharmaceutical industries.Traditional organic reactions for selective oxidation of alcohols to carbonyl compounds not only involve environmentally harmful and corrosive stoichiometric oxidants（e.g.Cr and Mn salts or V₂O₅）in organic solvents,but also produce large amounts of hazardous wastes under harsh conditions（e.g.high temperature and pressure）.In order to overcome these drawbacks,great efforts have been devoted to exploiting clean processes for green organic synthesis.Recently,photocatalysis emerged as a green and promising technique for organic synthesis,which is frequently carried out in aqueous medium under mild conditions without using toxic solvents and reagents.Among them,WO₃has been considered as one of the most ideal candidates owning to its outstanding stable physicochemical properties and wide applications in secondary batteries,gas sensors,electrolysis,and heterogeneous photocatalysis.（1）Herein,hierarchical yolk-shell WO₃ microspheres were synthesized through hydrogen ion-exchange route followed by thermal treatment,All the photocatalytic reactions were conducted under irradiation by using a 300W xenon lamp,analyzed by a gas chromatograph（Shimadzu,GC-2014C）equipped with a TB-1 column and a flame ionization detector（FID）.As expected,the photocatalytic activity during selective oxidation of aromatic alcohols to their corresponding aldehydes in aqueous medium under light irradiation with full wavelengths is WSS>WHS>WYS,which can be attributed to the synergistic promoting effect of the porous structure together with high surface area,small crystallite size,and enhanced light harvesting via multiple reflections in yolk-shell chambers.Moreover,all the WO₃photocatalysts displayed excellent durability against structural collapse due to the robust hierarchical structures.（2）In this work,uniform WO₃ nanorods with tailored surface oxygen vacancies were successfully prepared by a facile hydrothermal route for the first time,which exhibited highly enhanced photocatalytic activity for selective oxidation of alcohols to corresponding ketones in water medium.The physicochemical structural properties of uniform WO₃ nanorods have been comprehensively characterized and well correlated with their photocatalytic activities.Results indicated that the highly enhanced photocatalytic activity of uniform WO₃nanorods was ascribed to the synergistic effect of the following three aspects:firstly,the high surface area favored the adsorption and diffusion of alcohol molecules;secondly,the small crystallite size facilitated the fast transfer of photoelectrons,which shortened the transfer distance of photoelectrons,thereby restrained the recombination rate of photoelectron-hole pairs;finally,the surface oxygen vacancies acted as the photoelectron sinks could capture photoelectrons and promote their separation from holes.Meanwhile,the uniform WO₃nanorods also demonstrated strong stability owning to the highly stable crystal phase and robust morphological structure.