Syntheses And Photoresponse Of Titanium-Oxide Cluster Compounds

Titanium dioxide has been one of the most important semiconductor materials and widely used in photocatalysis,photovoltaic cells and sensors.The nature that titanium dioxide absorbs only ultraviolet of the solar spectrum greatly inhibits its applications,and hence extensive research has been performed on improving the light-absorption properties and the photocatalytic activities of it.On the other hand,in dye-sensitized solar cells(DSSC),the interfacial electron transfer from photo-excited dye molecules to semiconductor conduction band is a rate-limiting step.Therefore research on the binding modes of dye molecules on TiO2 surfaces has been an important focus about enhancing solar light conversion efficiency.Due to the complex structure of titanium dioxide,such as defects and disorders,it is extremely difficult to determine the precise chemical environment of dopants in TiO2 lattice and to characterize the binding modes of ligands on the surface.Polyoxotitanates(POTs),also known as titanium oxo clusters,are the molecular forms of titanium oxide.Taking the advantages of their single crystal structures,the structure-property relationships of POTs can be established more easily,which is inspiring for studies of TiO2 on structures,photoabsorption and electron transfer.Therefore,it is necessary to study the syntheses,doping with heteroatoms,structures,electronic structures,photophysical and photochemical properties of POTs.In this thesis,a series of metal doped and catechol surface-functionalized POTs are synthesized,with the aim of studying the structure-property relationships.The contents of this thesis are divided into three chapters as follows:In Chapter Ⅰ,the syntheses of titanium dioxide,the influence of ligand-functionalization,types and syntheses of polyoxometalates are reviewed,and the structure and properties POTs are summarized.Finally,the scientific significance of this thesis is highlighted.In Chapter Ⅱ,a series metal-doped isostructural POTs are synthesized,and the influence of the metal dopants on the photoabsorption and photocatalytic properties of POTs are studied.Using controlled hydrolysis method,17 isostructural POTs are synthesized,including the closed-shell metal-doped POTs,transition metal-doped POTs and monolacunary POT.The crystal structures are characterized by single crystal X-ray diffraction.The research indicates that although Co and Ni doping enhances the absorption of the solar light,it causes serious loss of UV photoactivity.Meanwhile,although loading of Ti vacancy does not enhance the light-absorption properties of a POT,it indeed improve the quantum efficiency of the solar spectrum.In Chapter III,a series of catechol-functionalized POTs are synthesized,and their structure and optical properties,ligand bonding modes and the electro-optical properties are characterized.Using solvothermal method and ligand-exchange method,6 catechol-functionalized POTs are synthesized and characterized.The research indicates that catechol ligand has several bonding modes on POTs cages,and interfacial electron transfer from catechol molecules to POTs cages can enhance the solar light conversion efficiency.