| Fossil fuels are the core of modern industrial power generation.Due to the growing energy demand and limited fossil fuel reserves,the development of sustainable clean energy technologies is necessary.Hydrogen energy has attracted widespread attention as a clean and sustainable energy source.To date,large-scale hydrogen production has relied on steam reformation or gasification of fossil fuels.Neither of these methods is environmentally friendly and sustainable.In the future,photocatalytic hydrogen evolution from water is considered to be an effective means in the field of generating hydrogen energy.In the past forty years,people have done a lot of work in developing new semiconductor photocatalysts,and hundreds of semiconductor materials have been researched.Among them,heterojunction photocatalysts can effectively improve the shortcomings of single semiconductor photocatalysts,such as narrow light absorption range,high recombination efficiency of photogenerated carrier,and the lack of active sites for photocatalytic hydrogen production.Heterojunctions have potential application in the filed of photocatalytic hydrogen production,The successful transmission of photogenerated carriers at the interface of the heterojunction is a prerequisite for constructing an efficient heterojunction photocatalyst,and the design of the interface structure of the heterojunction plays a key role in the transport behavior of photogenerated carriers.Furthermore,the heterojunction interface can be designed and constructed to increase the active sites of photocatalyst and achieve photocatalytic hydrogen evolution from water without Pt co-catalyst.In this paper,a series of heterojunction photocatalysts were constructed based on the bimetallic oxide zinc germanate(Zn2GeO4)and graphite-like carbon nitride(CN)through in-situ sulfurization technology.The evolution of interfacial structure in the in-situ sulfurization process of Zn2GeO4-x/ZnS and the superiority of in-situ sulfurization technology in the construction of ACN/Ag/Ag2S heterojunction was discussed respectively.The mechanism of photocatalytic hydrogen evolution from water without Pt co-catalyst was illuminated for Zn2GeO4-x/ZnS and ACN/Ag/Ag2S heterojunctions.The first chapter mainly introduced the research background and development history of semiconductor photocatalyst,as well as the basic principles of photocatalytic hydrogen evolution from water and the main factors of restricting photocatalytic efficiency.The research status and problems of heterojunctions design,the influence mechanism of interface structure evolution on photocarrier transport and photocatalytic performance are expounded.On this basis,we introduced the research ideas and research content of this research work.In the second chapter,we successfully constructed Zn2GeO4-x/ZnS heterojunction by in-situ etching sulfurization method.Adopting the in-situ etching technology to construct Zn2GeO4-x/ZnS heterojunction photocatalysts,the migration and precipitation of constituent elements can result in the reconstruction of the interface and the formation of defects.The reconstructed interface can enhance the close recombination between the catalyst components and promote the photogenerated carrier transport between the Zn2GeO4-x/ZnS heterojunctions;on the other hand,during the in-situ etching sulfurization process,the surface of Zn2GeO4 nanorods evolved from a flat(100)crystal plane to a rough topological structure composed of(110)and(113)crystal planes with catalytic active centers Ge3c4+and Ge3c3+-Vo,respectively.There is a new strategy to improve the photocatalytic water-splitting activity without the use of the Pt co-catalyst by the synergism between interface engineering and defect control.The ZGO/ZS-0.02 heterojunctions exhibited the optimum photocatalytic H2 production(533 μmol h-1 g-1),which is approximately 5 and 7 times higher than those of pristine Zn2GeO4 and ZGO/ZS-0.5(ZnS),respectively.In this work,in-situ etching sulfurization are used to design the interface structure,and a heterojunction with a topological structure,which realized the photocatalytic hydrogen evolution from water without Pt co-catalyst.This work provides a new strategy for the design of efficient photo catalysts.In the third chapter,we focus on the problems of poor conductivity,narrow photoresponse range and the lack of active sites of CN for photocatalytic hydrogen evolution,and we doped metal elements with CN and constructed heterojunction to improve its photocatalytic performance.First,by doping with element Ag,the heptazine ring of the CN structural unit was opened,and the electron accepting group-C≡N was successfully introduced,which promoted the separation of photogenerated carriers in the CN layers.At the same time,Ag doped between the CN layers,which increases the conductivity of the CN.Then Ag is deposited on the the photocatalyst surface,which effectively broadens the light absorption range.Finally,the ACN/Ag/Ag2S heterojunction was successfully constructed by chemical vapor deposition sulfurization,and the Ag2S as co-catalyst.The photocatalytic hydrogen evolutiont rate of ACN/Ag/Ag2S-1 could reach 105 μmol h-1 g-1,which is 6 times that of pure CN.In this work,the interlamination/the in-plane of CN is doped with Ag and deposited Ag on the surface of ACN,and constructed the ACN/Ag/Ag2S heterojunction by in-situ sulfurization.The heterojunction photocatalyst with different chemical states of Ag to achieve the different roles of Ag and realized the photocatalytic hydrogen evolution from water in visible light by the synergism between the different of Ag.In the last chapter,we systematically summarize the research content of this thesis,the research innovations,and look forward to the next work. |
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