| The rapid development of science and technology has brought great convenience to human life,but it is also accompanied by many energy and environmental problems.Energy crisis and environmental pollution have become unavoidable problems in the process of social development.Among many new clean energy sources,solar energy reserves are extremely abundant.Driven by solar energy,photocatalysts can realize reactions such as water splitting to produce hydrogen,CO2 reduction,and synthesis of fine chemicals,which have great application prospects in solving energy and environmental problems.At present,the utilization of solar energy is still unsatisfactory,so improving the utilization of solar energy has become the focus of research.In the field of photocatalysis,the localized surface plasmon resonance(LSPR)can greatly enhance the absorption of solar energy by nanocatalysts,thereby effectively improving the utilization of solar energy.The essence of the SPR effect is the interaction between free carriers and incident photons,so the level of carrier concentration will directly affect the SPR characteristics of the material.At present,the research carriers of the SPR effect mainly include noble metals and heavily-doped semiconductors.Among them,metal-based SPR materials have a high free carrier concentration,and the spectral response range is mainly concentrated in the visible region.However,most metal-based SPR materials have a low utilization of infrared light.Compared with metal materials,heavily-doped semiconductor-based SPR materials have a lower free carrier concentration,and thus can effectively utilize near-infrared light.At the same time,the free carrier concentration of heavily-doped semiconductors is closely related to the doping degree,so the SPR characteristics can be adjusted by changing the doping concentration.However,heavily-doped semiconductors have low utilization efficiency of visible light.Thus,metal and heavily-doped semiconductor materials have their own limitations,and the reasonable combination of them to form a composite system can effectively utilize the advantages of both.The composite system can not only effectively improve the spectral response range,but also generate a "hot spots effect" through near-field coupling,thereby increasing the light absorption cross section,promoting the excitation and separation of carriers,and enhancing the transport efficiency of charge carrier.Therefore,it is expected to significantly improve the utilization of solar energy and the catalytic performance of the catalysts.However,there are few studies on the metal/heavily-doped semiconductor composite system,and the coupling effect and energy transfer mechanism between metal and heavily-doped semiconductor are still unclear.This seriously hinders the scientific construction of the metalheavily doped semiconductor composite system,and is not conducive to further expanding the application of the SPR effect in the field of photocatalysis.Therefore,in order to study the coupling effect and energy tran sfer mechanism between metal and heavily-doped semiconductor,lightly-doped WO3-x was studied firstly,revealing the influence of strain on oxygen vacancies and catalytic reactions.Subsequently,a metal/heavilydoped semiconductor(Au-W18O49)double plasmon composite system was constructed.The coupling effect and hot electron injection(HEI)mechanism between Au and W18O49 were fully studied.On this basis,the plasmon induced resonance energy transfer(PIRET)mechanism in the Au-Al2O3-W18O49 composite system was further verified.Then,in order to study the effect of carrier concentration on the SPR characteristics in composite system,the effect of laser bombardment on the controllable synthesis of WO3-x powder was initially explored.The specific research contents of this thesis are as follows:In chapter 1,the basic principle and commonly used modification strategies of photocatalysis are briefly summarized,and then the physical meaning,influencing factors and energy relaxation mechanism of the localized surface plasmon resonance(LSPR)effect are introduced.After that,the research progress of metal,heavily-doped semiconductor and metal/heavilydoped semiconductor composite system in SPR enhanced photocatalysis are fully discussed,focuses on the analysis of the advantages of the composite system and the existing problems in the current research.Then introduces the advantages of single-particle spectroscopy in studying mechanisms of SPR-enhanced catalysis are introduced.On this basis,we finally expounded the significance of selected topic and the main research contents of this thesis.In chapter 2,research on lightly-doped WO3-x films with low free carrier concentration was conducted.We adjusted the oxygen vacancy concentration of WO3-x thin films by strain,and explored the effect of oxygen vacancies on the catalytic activity of reverse water gas shift reaction.Compared with WO3-x powder,WO3-x film has higher catalytic activity and significant photothermal synergistic effect,which is due to the higher concentration of oxygen vacancy in WO3-x film with the assistance of strain.A higher concentration of oxygen vacancy means stronger SPR light absorption,more CO2 adsorption sites and more favorable energy band structure.The above three points effectively improved the catalytic activity of the lightly-doped WO3-x film.In chapter 3,we constructed a metal/heavily-doped semiconductor(Au-W18O49)composite system using W18O49 with a high free carrier concentration as the research carrier,and applied it to the hydrogenation reaction of p-nitrophenol.Relevant characterizations and theoretical calculations prove that the Au-W18O49 composite system can effectively expand the spectral response range and produce near-field coupling effects.In addition,the single-particle fluorescence spectroscopy demonstrated the existence of the HEI process between components.This coupling effect and the HEI process can effectively improve the SPR catalytic performance of the composite system.Based on the study of the HEI mechanism in Au-W18O49 composite system,chapter 4 further verified the PIRET mechanism in the Au-Al2O3-W18O49 composite system.In this chapter,we utilized atomic layer deposition(ALD)technology to introduce Al2O3 insulating layer between Au and W18O49,and successfully constructed Au-Al2O3-W18O49 composite system.The Al2O3 insulating layer effectively shielded the HEI process between Au and W18O49,which laid the foundation for the study of the PIRET mechanism.Then we proved the existence of the PIRET mechanism in the composite system through performance comparison,photoelectrochemical test and single particle fluorescence spectrum analysis.In chapter 5,in order to study the effect of carrier concentration on the SPR characteristics of the metal/heavily-doped semiconductor composite system,we initially explored the effect of laser bombardment on the controllable synthesis of WO3-x ultrafine powder.Using H2WO4 and WO3 as reaction targets,we bombard the targets with 1064 nm laser.The oxygen vacancy concentration of WO3-x ultrafine powder can be adjusted by changing the atmosphere conditions.After preliminary exploration,a laser-assisted synthesis technology was developed to controllably produce WO3-x ultrafine powder.In the last chapter,the main work of this thesis was summarized.We concluded the innovation points as well as the deficiencies of this thesis,and made an outlook for the next research work. |
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