TiO₂ Based Multishelled Hollow Spheres For Photocatalytic Water Oxidation

Energy and environment issue have become the highlight in global scale.Due to exhaustion of fossil fuels,followed by the pollution of environment,developing cheap and clean energy from wide range of sources becomes more and more important.Solar energy,a widespread environmentally friendly and renewable energy has been studied for long time.Nowadays,one of the major methods to take advantage of solar energy is to convert solar energy to chemical energy.As it is acknowledged that the energy density of sunlight is very low and nonuniform,effective utilization of solar energy becomes particularly important.In this work,we analyze the challenges and problems in solar water splitting,and synthesis unique nanostructure materials.Furthermore,we apply them in solar water splitting.TiO2 and Fe2O3 can fulfill the principle requirements for solar water splitting.Demerits of TiO2 are:large bandgap??3.2 eV?,which constitute only 4%of the solar energy spectrum and minority carrier rapid recombination due to the trap densities.Fe2O3 harvest visible light which consists 46%of the solar energy spectrum,stable in aqueous solution,abundant,nontoxic and low cost.However,the low electrical conductivity of hematite disrupts the continuous process of charge generation,transportation,collection and injection which resulting in the substantial loss of energy due to rapid electron-hole recombination.One potential approach towards the solution of intrinsic shortcoming with Fe2O3 and TiO2 is to develop heterojunction Ti-Fe-O?Fe2TiO5?pseudobrookite.To address whether Fe2TiO5 alone can solve the intrinsic problems with TiO2 or Fe2O3 and drive the four hole chemistry efficiently or TiO₂ is mandatory to shuttle the photo-generated electric charges between the two systems,we design and synthesized multi-shelled Fe2TiO5 and Fe2TiO5-TiO2 composite hollow spheres with specific ferric concentration to utilize the heterojunction between Fe2TiO5-TiO2 phases to achieve enhanced water oxidation.The advantages of our design multi-shelled hollow spheres are as follows:1)A void hollow cavity with low material density enhances the surface area,hence more reactive sites available for the catalytic reaction 2)the porous surface enables the solvent to access the reactive sites of the shells hence collect the minority carriers efficiently.3)The forward and backward constructive interference at the surface of nanoshells enhance the incident photon life time in the material.These unique features of our design catalysts make it a promising candidate in photocatalytic water splitting.The aim of this thesis is to provide the synthetic mechanism study by combining and controlling the Ti/Fe ratio in the nanoshells around the hollow cavity and investigate the water oxidation efficiencies related to a morphological aspect of designed composites.A series of crystalline metals oxides and mixed metal oxides multi-shelled hollow spheres were successfully synthesized such as TiO2,Fe2TiO5-TiO2,Fe2TiO5,Fe2TiO5-Fe2O3,Fe2O3,Fe2O3-TiO2,NiO,Co3O4,Mn2O3,and Fe2TiO5-TiO2-Ag2O and checked the activity towards photocatalytic water oxidation half reactions.