Preparation Of Modified Titanium Dioxide Composite Photocatalysts And Their Application And Mechanism Investigation In Hydrogen Evolution

Hydrogen（H₂）energy,owing the advantages of recyclability and environmental friendliness,has been considered as an ideal energy source that can replace the traditional fossil energy.The development of non-toxic,efficient,and low-cost methods in producing H₂has become a hot topic.Among the various strategies,H₂evolution from photocatalytic water splitting has been regarded to be the most promising way in solving the energy and environmental problems.Titanium dioxide（TiO₂）is the most classic semiconductor among various photocatalysts.It possesses the advantages of high photocatalytic efficiency,strong chemical inertia,low cost and high stability,making it a powerful candidate for photocatalytic H₂evolution,pollutants photodegradation,atmospheric purification,sterilization and disinfection.However,TiO₂only responses to ultraviolet light absorption because of its large bandgap of ca.3.20 e V.Meanwhile,the photocatalytic activity of TiO₂is greatly restricted due to the fast charge recombination rate and low charge transport ability.Therefore,the effective modification of TiO₂is crucial in improving its photocatalytic activity by broadening visible light absorption ability,reducing the photogenerated electron-hole recombination rate and accelerating the charge transfer efficiency.Moreover,the study on the charge dynamic kinetics in TiO₂during the photocatalytic processes is still limited.The deep understanding of the photocatalytic mechanism in TiO₂can be an important fact in designing and developing efficient TiO₂photocatalysts.In this thesis,a series of modification strategies have been conducted to improve the photocatalytic activity of TiO₂,including the heterostructure construction and the deposition of metal single atom cocatalyst.The time-resolved femtosecond transient absorption spectroscopy has been employed to investigate the charge dynamic kinetics in the as prepared TiO₂-based photocatalysts.Specific findings and results are as follows:（1）In situ construction of elemental phosphorus nanorod-modified TiO₂photocatalysts for efficient visible-light-driven H₂generation.In this study,a red phosphorus（RP）/TiO₂composite system was constructed via a chemical vapor deposition strategy.The evolution of the fibrous phased RP nanorods on the surface of anatase TiO₂spheres was rationally adjusted by controlling the composition of precursors.The optimal RP/TiO₂composite exhibited a significantly enhanced visible light-driven photocatalytic H₂generation rate of 681μmol h^-1g^-1.The tightly interior surface bonding between RP and TiO₂greatly promoted the efficient charge transfer and redistribution,resulting in prolonged lifetimes of the active charges during the photocatalytic process as investigated in detailed using femtosecond time-resolved transient absorption（fs-TA）spectroscopy.（2）Preparation of Pt single-atom deposited TiO₂（Pt₁/TiO₂）photocatalysts for efficient H₂generation.In this study,Pt₁/TiO₂was fabricated via a precipitation-deposition strategy.Pt single atoms were stabilized in the surface defects of TiO₂.The optimal Pt₁/TiO₂composite exhibited a significantly enhanced photocatalytic H₂generation rate of 670μmol h^-1g^-1.It is discovered that the modification of Pt single atoms effectively extended the spectral absorption of TiO₂to visible light region.In addition,Pt single atoms on the surface of TiO₂acted as the reduction sites in improving the H₂production rate.Moreover,the synergistic effect between Pt single atom and TiO₂promoted the efficient charge transfer and redistribution,which restricted the charge recombination efficiency in TiO₂.