Construction Of Defective Tungsten Oxide And Tungsten Oxide-based Heterostructures And Their Applications

Tungsten oxide is an n-type semiconductor,which has received considerable attention due to its earth-abundance and highly tunable composition.Tungsten oxide includes stoichiometric WO3 and sub-stoichiometric WO3-x.The introduction of oxygen vacancies in WO3 will greatly change the electronic structure and properties of material,and the mechanisms of oxygen vacancies with different contents are also different.The formation of oxygen vacancies generally creates new defect levels in the forbidden band and increases the free carrier density in tungsten oxide.When the oxygen vacancy content is low.these defect levels allow electrons transition from valence band to defect levels or from defect levels to conduction band,resulting in the narrowing of band gap of tungsten oxide and enhancement of light absorption in visible and even near-infrared region,which is beneficial to the improvement of photoeatalytic activity.When the oxygen vacancy content is high,the resulting high free carrier concentration in WO3-X can induce LSPR,which will significantly enhance the optical absorption of defect tungsten oxide in visible or near-infrared region.The LSPR of this metal-free plasmonic material is not only tunable,but also highly sensitive to the external environment,so it can be applied to various fields such as bio-sensing.In addition.LSPR of WOs-x greatly extends the light absorption of material,so it is also widely used in the field of photocatalysis.However,the hot electrons generated by LSPR are easy to self-cooling,and the construction of metal/semiconductor heterostructures is an effective strategy to improve the efficiency of hot electron transfer and carrier separation,Therefore,this paper studies the formation of defects in tungsten oxide and their effects on the properties of material.The preparation of metal/plasmonic tungsten oxide heterostructure is also explored,and the defective tungsten oxide and tungsten oxide-based heterostructure are used in the fields of photocatalysis and bio-sensing.The main research contents are as follows:(1)Fabrication of defective WO3-x nanobelts and their visible-light photoelectrocatalysisDefective WO3-x nanobelts are prepared by one-step solvothermal method,and the oxygen vacancy content is tuned by changing the experimental conditions.Through comparative studies,defective WO3-x nanobelts have significantly enhanced photoelectrocatalytic performance,which is mainly due to the introduction of oxygen vacancies.The introduction of oxygen vacancies reduces the optical band gap and expands the light absorption range of material.The construction of oxygen vacancies also increases the free carrier density in tungsten oxide,resulting in an increase of conductivity of material.(2)Synthesis of sub-stoichiometric WO3-x with tunable LSPR for biosensingSub-stoichiometric WO3-x has been successfully prepared by a simple chemical reduction method,which exhibits strong plasmon resonance absorption in the visible and near-infrared regions.Through changing the reaction temperature,we can regulate the properties of LSPR.In the optical detection system using bovine serum albumin as a model molecule,sub-stoichiometric WO3-X exhibits potential for quantitative detection of organisms.(3)Fabrication of Ag/WO3-x heterostructure and its application in photocatalysisAg/WO3-x heterostructure has been fabricated by a wet chemical reduction and it exhibits the largest light absorption in the visible and near-infrared regions,which is a result of combination of band gap with LSPR absorption of WO3-x and LPSR absorption of Ag.In the photocatalytic degradation experiment of methylene blue.Ag/WO3-350 exhibits the strongest photocatalytic activity,in which plasmon resonance of WO3-350 plays an important role.