Performance And Mechanism Study Of Modified TiO₂ For Photocatalytic Hydrogen Evolution

With the rapid development of the world economy,people’s demand for energy is increasing day by day.However,the reserves of traditional energy are about to be exhausted,and the environmental pollution and energy crisis caused by the burning of traditional energy have posed a threat to the survival of human beings.Therefore,it is highly desirable to find green and renewable energy sources.Hydrogen energy has many advantages,such as zero emissions and high energy density values per unit mass.Therefore,hydrogen energy stands out from many new energy sources and has become a kind of clean energy with broad prospects.Photocatalytic technology can use sunlight to drive a series of important chemical reactions,which has the characteristics of low cost and environmental friendliness.Photocatalytic technology,which uses sunlight to drive a range of important chemical reactions,has the advantages of low cost and environmentally-friendly.Solar energy can be converted to hydrogen energy through photocatalytic water splitting technology,which is one of the ideal ways of clean energy production and environmental pollution control in the future.TiO₂has attracted intensive attentions as photocatalytic materials for its appropriate energy band position,high chemical stability,low cost and nontoxicity.However,the intrinsic shortcomings of TiO₂materials,e.g.,slow electron transfer and rapid recombination of photogenerated charge carriers drastically,have limited their practical application.Therefore,the focus of this dissertation is to improve TiO₂through surface modification.The main research contents are as follows:1.Modification of non-noble metal Cu nanoclusters and preparation of high specific surface area materials were combined to improve the performance of TiO₂photocatalytic hydrogen evolution.A promising hydrangea-like TiO₂support with enhanced photocatalytic performance enabled by enlarged surface area is synthesized via a simple hydrothermal method.Then,ultrafine（～1 nm）Cu clusters were further loaded onto the hydrangea-like TiO₂supports.A maximal hydrogen evolution value of3.7 mmol h^-1g^-1was obtained in the optimized system of 6Cu-TiO₂（6 wt%Cu）,which is about 2-fold higher than that of bare hydrangea-like TiO₂.Experimental result and theoretical analysis confirm that Cu nanoclusters optimize the kinetic process of carriers.Notably,ultrafine Cu clusters as the co-catalyst on the surface of TiO₂can act as active sites to capture the electrons through modulating interfacial charge transfer process.Secondly,hydrangea-like TiO₂has a large specific surface area,which provides more active reaction sites for the catalytic reaction and lead to excellent photocatalytic hydrogen evolution performance.2.TiO₂was modified by oxygen vacancy and non-noble metal Cu single-atom to optimize the performance of TiO₂photocatalytic hydrogen evolution.First,the TiO₂were thermal treated at reducing atmosphere for 1 hour with different temperatures（reducting gas contains 5vol.%hydrogen and 95 vol.%argon）to achieve defective supports with surface oxygen vacancies.Atomically dispersed single atom Cu on TiO₂was synthesized.They would be assembled spontaneously through the electrostatic interaction.The Cu-O_v/TiO₂catalysts exhibited 26.6 times higher photocatalytic activities that O_v/TiO₂.Experimental results show that the kinetic behavior of carriers is optimized by introducing oxygen vacancies and Cu single-atoms,which promotes the effective separation and transfer of photogenerated carriers.Meanwhile,the O_vhas been demonstrated to facilitate the adsorption and activation of water molecules,and the Cu site of Cu-O_v/TiO₂promote the formation of hydrogen by combining two hydrogen atoms.Therefore,the excellent catalytic performance of the Cu-O_v/TiO₂photocatalyst should be attributed to the synergy of the atomic Cu and O_v.These findings provide an effective strategy for combining the single-atom with defect engineering for modifying photochemical and photophysical performances.