Study Of Facet Effect And Interfacial Schottky Barrier Based On TiO₂ Nanocrystals

With the increasing demand for resource and serious environmental pollution,how to efficiently collect,convert and store solar energy,a renewable and clean energy,has become a challenging and indispensable topic.Recently,the facet effect in semiconductor nanocrystals has been extensively examined in the photocatalytic water splitting,which is mainly manifested in the separation of photogenerated charges under the in-built electric field induced by surface states.A deep understanding of such effect is not only helpful to further improve the catalytic performance of materials,but also provides some hints for exploring the other photophysical or photochemical processes concerning the surface and interface.Anatase TiO2 is one of the most widely used materials in solar energy conversion.The studies of photochemical reactions on TiO2 surface and related interfacial electron transfer process play an essential role for improving the efficiency of phtotocataysis and photovoltaic luminescent devices.Based on the controllable synthesis of semiconductor nanocrystals and theoretical calculation of electronic structure of materials,the thesis mainly demonstrates the research work during my master period:1.With respect to assisting the laser desorption/ionization process(LDI),nanomaterials as novel matrix have been proved to fill in gaps for MALDI detecting the low molecular weight samples,where the the structure-activity relationship is still lacking.Anatase nanocrystals with different surface structures,denoted as TiO2(001)and TiO2(101),were synthesized along with the application to the analyzing amino acids in MALDI-TOF.The(001)dominated TiO2 nanoplate was found to be well co-crystallized with amino acids without fragmenting the analyte under laser irradiation.The characteristic molecular ion peak can emerge from the mass spectra with good sensitivity.The explicit comparison between TiO2(001)and TiO2(101)for considerable LDI is attributed to the facet effect of photocatalysis.2.On account of the complexity of periodic systems,it remains a huge gap in theoretical describing the photophysical or photochemical process accurately.Firstly,using the density functional theory(DFT),the surface work function of TiO2(001)and(101)was compared.In addition,the photogenerated holes and electrons in surface heterojunction model were localized around the oxygen on(001)and titanium on the(101),respectively,which may account for the underlying mechanism of facet effect in MALDI enhancement.Futhermore,combining the TiO2 with plasmonic metals is attractive in photocatalysis,making full use of visible light.On this basis,we also construct the heterostructures of Au(110)-TiO2,where the structural effect and electronic effect are non-negligible at the interface between two facets..By considering the electron transfer process in two systems,the microscopic physical image of Schottky barrier height was confirmed.