Synthesis Of Tin/Tantalate-base Photocatalysts And Their Photo-catalyzed Hydrogen Evolution Form Water

Energy crisis and environmental issues act as two major challenges today.Especially the rapid increase of fuel demand ignites the passion for exploring clean,safe and sustainable energy resources.Hydrogen energy is clean energy.Photocatalytic hydrogen production from water over semiconductor oxides under solar irradiation is one of the most efficient,ecofriendly methods.As a typical n-type semiconductor,SnO2 has attracted a lot of research in the fields of photocatalysis and solar cells due to its excellent optical properties.However,few applications of Sn02 have been reported for photocatalytic hydrogen production due to the quick recombination of photo-generated charge carriers and large band gap.Therefore,suppressing the recombination of charge carriers and decreasing the large band gap are essential for improving its photocatalytic hydrogen production performance.On the other hand,CsTaWO6 is a high efficient photocatalyst.Nevertheless,the large band gap limits its practical application in photocatalysis under visible light irradiation.Recent years,several strategies such as doping,compositing,noble metal depositing have been adopted to achieve visible light response in the field of semiconductor photocatalysis.In this thesis,tin-oxide and CsTaWO6 were used as researched targets,where doping and semiconductor combination methods were conducted inorder to improve the optical property and photocatalytic activity.Based on the experiment results and theoretical calculation,the band gap engineering mechanism was studied.The main contents are as follows:(1)A series of nonstoichiometric tin oxides that exhibited highly efficient visible light photocatalytic reactivity toward water reduction were prepared through solvothermal method with controlled temperature.The chemical composition and charge state of tin oxides were investigated by XPS spectroscopy.The results indicated that both Sn2+ and Sn4+ were coexisted in SnOx samples.SnOx prepared under room tempreture exhibited excellent and high visible light photocatalytic activity toward H2 evolution.However,the photocatalytic activity of SnOx gradually decreased with an increase of reaction temperature.This may be due to the driving force of reduction decreased with the diminished Sn2+.Large amounts of hydroxyl groups,Sn2+ and relatively negative potential of conduction band in nonstoichiometric tin oxides play critical roles in visible light harvesting and photocatalytic water splitting.This work provides a novel strategy for the development of highly efficient photocatalytst.(2)Sn2+ self-doped SnO2 nanomaterials were prepared through precipitation method.IR and Raman analyses showed that the structure of SnO2-x had not changed after self-doping.The photocurrent response showed that SnO2-x possessed an excellent response to visible light.Photocatalytic hydrogen production under visible light test showed that the photocatalytic activity gradually improved with the increased content of Sn2+.Sn2+ self-doping can effectively reduce the energy band gap,at the same time,abundant of hydroxyl groups contribute to the uplifting of the conduction band,which can dramatically enhance the photocatalytic activity toward water reduction.(3)CsTaW06 was synthesized via a solid-state method and a series of CsTaWO6/g-C3N4 composite photocatalysts were prepared.CsTaWO6/g-C3N4 composite photocatalyst had a stronger photocurrent and smaller impedance than CsTaW06.Photocatalytic water splitting reaction under visible light irradiation was investigated.It was found that the CsTaWO6/g-C3N4 obviously improved the photocatalytic activity.Due to the matched band edge alignment of CsTaW06 and g-C3N4,photo-excitation electron of g-C3N4 transfered to the CB of CsTaWO6.Thereby,the photon-generated electrons and holes can effective separate and the subsequent photocatalytic activity enhanced.