Fabrication Of Tungsten Oxide Based Heterojunction Photocatalyst With Improved Photoelectrochemical Performance

Semiconductor photocatalysis has been intensively investigated in recent years as it is potential in the applications to solve environmental and energy issues.Tungsten oxide-based photocatalysts are widely used in the photocatalytic degradation of organic contaminant and water splitting due to their capacity of visible light absorption and easy fabrication.However,tungsten oxide still suffers from the difficulties of the low quantum yield and high photo-excited electron-hole pairs recombination.These disadvantages,to a large extent,limit the development of tungsten oxide-based photocatalysts.Lots of attempts have been made to improve the photocatalytic performance.Among them,heterogeneous structure is considered as one of the effective strategies to design new photocatalysts since its inner electric field could provide the driving force to promote photo-excited electron-hole pair separation and thus improve the quantum yield of photocatalysts.Based on the problems of semiconductor photocatalytic technology that exist in practical application,this thesis combined the experimental studies with theoretical simulation to design semiconductor/semiconductor heterojunction and metal/semiconductor heterojunction,and further discussed the mechanism of the improved photocatalytic acticity.On one hand,based on the different crystal structures of tungsten oxide,we fabricated a homojunction photocatalyst by combine hexagonal and cubic tungsten oxide,investigated the microscopic mechanism of the homojunction and revealed the synergic relationship of photo-response capacity,electronic mobility and energy level matching.On the other hand,we fabricated Schottky-junction by loading Au nanoparticles on tungsten oxide film,discussed the mechanism of Au in the aspect of improving the photoelectrochemical performance of tungsten oxide and proposed the bifunctional feature of Au nanoparticles.Our studies provide guidance for the design of efficient visible light photocatalysts.The main researches are listed as follows:The first chapter mainly introduced the research background of this thesis,including the development and research status of photocatalysis,tungsten oxide-based photocatalyst and the applications of fabricating heterojunction.In addition,the research ideas and main content of this thesis were briefly introduced.In the second chapter,we took homojmunction as the main guidance,based on the different crystal structures of tungsten oxide,a homojunction with different phases of tungsten oxide photocatalyst was prepared via a hydrothermal method by adjusting the pH value.Besides,we investigated the mechanism of fabricating tungsten oxide homojunction photocatalysts,and revealed the harvest of visible light,the energy level matching,and the carriers' transport rate were all important for improving photocatalytic activity.SEM and HRTEM analysis showed the homojunction consisted of tungsten bronze-type?hexagonal?and pyrochlore-type?cubic?structures.The rod-like hexagonal phase inserted into block cubic phase to form a well-defined homojunction structure under the proper pH condition.The activity of photocatalyst was tested through degradating RhB and water oxidation.The results indicated the homojunction photocatalyst displayed a higher photocatalytic activity compared with individual tungsten oxide under visible light and simulated sunlight irradiation.The further investigation revealed the inner electric filed at the interface of the homojunction facilitated the separation of electron-hole pairs,resulting in the improved photoelectrochemical performance.The present work provided a promising method for the development of efficient tungsten oxide photocatalysts.In the third chapter,we took Schottky junction as the main guidance,and a series of Au/WO₃ Schottky-junction photoanodes were prepared by loading Au nanparticles with different amounts on WO₃ film.Besides,We investigated the mechanism of the improved photoelectrochemical performance of Au/WO₃,and revealed the enhanced performance is attributed to the two effects of the loaded Au nanoparticles.XRD,SEM and XPS analysis indicated that we successfully obtained a series of Au modified WO₃ photoanodes by an immersing-calcination method.HRTEM and UV-vis indicated that the 10?20 nm Au nanoparticles showed a significant surface plasmon resonance,which induced the light adsorption at around 560nm wavelength.The Mott-Schottky measurement and theoretical calculation indicated that an inner electric field was built at the Au/WO₃ interface,which would promote the separation of the photo-excited electron-hole.The synergistic effect of SPR and the inner electric field improved the PEC performance of the Au/WO₃ photoelectrodes.However,we also noted the loaded amount of the Au nanoparticles should be carefully considered due to the introduction of the recombined centers.The work could provide a promising approach for the development of efficient homojunction photocatalysts.In the last chapter,we summarized the conclusions and innovation of this dissertation,and previewed the further studies.