Controllable Synthesis Of Gold Nanocrystal/Ceria Heterostructures For Nitrogen Photofixation

The utilization of solar energy to drive challenging chemical reactions offers promising opportunities to address the energy demands and environmental issues.However,the wide bandgaps of conventional oxide semiconductor photocatalysts bring about the weak light response and poor photocatalytic activity in the visible and near-infrared（NIR）regions.An appealing route to solve these issues is the integration of traditional oxide semiconductors with plasmonic nanocrystals（e.g.,gold nanocrystals）,known as plasmonic photocatalyst.Au nanocrystals possess unique localized surface plasmon resonance（LSPR）properties,which can not only endow Au nanocrystals with strong response to the visible and NIR light but also generate high energy hot carriers.When the semiconductor is hybridized with Au nanocrystals,the visible and NIR light photocatalytic activity of semiconductor photocatalyst will be enhanced through a plasmonic sensitization mechanism.CeO₂ is a wide bandgap n-type semiconductor and is widely applied as the photocatalyst in various reactions.The integration of Au nanocrystals with CeO₂ semiconductor photocatalyst to form Au/CeO₂ heterostructures is a promising way to improve the photocatalytic activity of CeO₂materials.However,the photocatalytic activity of Au/CeO₂ heterostructures is largely dependent on the spatial arrangement of the two components.In contract to the core@shell nanostructures that the activity sites of metal core are totally covered by the semiconductor shell,the ideal plasmonic photocatalysts should have spatially separated structures,allowing for the hot electrons and hot holes participation in the reaction simultaneously.In this thesis,we developed two types of spatially separated Au/CeO₂ heterostructures,the"dumbbell-shaped"Au/end-CeO₂ and the Janus Au/Ag/CeO₂ heterostructures,and studied their applications in photocatalytic nitrogen fixation as follows:1.The"dumbbell-shaped"Au/end-CeO₂ nanostructures wereobtained through the selective growth of CeO₂ shell on the two ends of Au nanorods.Systematical investigations have showed that the bifunctional ion,the surfactant concentration,and the selection of ceria precursor were all crucial to the site-selective growth behavior.The presence of abundant oxygen vacancies,the spatial separation nanostructure and the plasmon-induced hot carriers make the Au/end-CeO₂nanostructures an excellent NIR N₂ photocatalyst.The photocatalytic N₂ fixation activity of the Au/end-CeO₂ sample is 6.2-fold compared with that of the core@shell nanostructures.2.The Janus gold nanosphere（AuNS）/Ag/CeO₂ nanostructures were prepared using the hard template method and applied to the visible light photocatalytic nitrogen fixation.The CeO₂ shell was successfully grown on the half surface of AuNSs through the use of SiO₂ hard template and autoredox reaction.Compared with the core@shell structures,the prepared Janus Au/Ag/CeO₂sample exhibited higher photocatalytic activity toward visible-light nitrogen fixation,benefiting from the spatially separated heterostructure and the wide light-response range.The N₂photofixation rate of the Janus Au/Ag/CeO₂ is 28.1μmol·h^-1·g^-1,which is 2.3-fold compared with that of the Au@CeO₂ nanostructures.In summary,two types of spatially separated Au/CeO₂ heterostructures were prepared and their applications in the N₂ photofixation were carefully investigated in this thesis.We postulate that the proposed selective growth strategies will motivate the rational design of various spatial-separated plasmonic nanostructures for novel photocatalytic applications.