Surface Engineering Of TiO₂ Nanostructures For Photocatalytic Selective Benzyl Alcohol Oxidation Coupled With H₂ Evolution

Hydrogen energy is considered as the most promising clean energy due to its zero carbon-emission and high energy density.However,the traditional industrial hydrogen production is energy-intensive and highly polluting.Developing efficient and environmentally friendly strategies for hydrogen production is of great significance.Photocatalytic technology that can convert solar energy into chemical energy has attracted wide attention.However,the photocatalytic hydrogen production from water splitting is greatly limited by the slow kinetics of water oxidation half-reaction.The photocatalytic reaction system combining hydrogen production with benzyl-alcohol oxidation can make full use of photogenerated electrons and holes to produce hydrogen and benzaldehyde simultaneously,thus realizing the efficient conversion of solar energy.Benzaldehyde is an important chemical raw material and widely used in the production of fragrances,candies and pharmaceuticals.Developing photocatalytic materials with excellent performance for the hydrogen production coupled with selective oxidation of benzyl alcohol is of great significance.Titanium dioxide（TiO₂）is recognized as the most promising photocatalytic material due to its distinct merits like environmental friendliness,high stability,and low price.However,the rapid recombination of photogenerated electrons and holes,limited photoabsorption,and insufficient catalytic active sites often limit the photocatalytic applications of TiO₂.Based on the preparation of TiO₂ submicron-spheres with high specific surface area,this thesis focuses on the surface modification of TiO₂ nanostructures to improve the photocatalytic performance toward hydrogen production coupled with selective oxidation of benzyl alcohol.Strategies such as anchoring Ru single atoms and Ru O₂ nanoparticles,or semiconductor quantum dots on TiO₂ submicron-spheres were adopted,which could achieve the multiple purposes including broadening the photoresponse range,promoting rapid separation of photogenerated electrons and holes,and providing abundant catalytic active sites.Therefore,the photocatalytic performance was enhanced.Finally,the photocatalytic mechanism was proposed based on experimental analysis and theoretical calculations.The main research contents of this thesis are as follows:1.The TiO₂ submicron-spheres with high specific surface area and abundant amino groups were prepared by a solvothermal method,and the Ru/TiO₂-NH₂ precursor was obtained via an impregnation-adsorption process where the surface amino groups help to stabilize Ru³⁺on TiO₂.Subsequently,the Ru _SA-Ru O₂/TiO₂ photocatalyst containing Ru single atoms（SA）and Ru O₂ nanoparticles was successfully constructed by a one-step thermal transformation process.This one-step method simplifies the preparation of photocatalysts and has more advantages than the previous multi-step modification methods for fabricating dual co-catalysts on semiconductors.The co-modification of Ru SA and Ru O₂ nanoparticles not only improved the separation efficiency of photogenerated electrons and holes but also provided efficient active sites for photocatalytic selective oxidation of benzyl alcohol and hydrogen production.The synergistic effect of multiple active sites enabled the Ru _SA-Ru O₂/TiO₂ photocatalyst to exhibit the high production rates of hydrogen and benzaldehyde.Detailed characterization and theoretical calculations further verified the synergistic mechanism of Ru SA and Ru O₂ nanoparticles in the photocatalytic reaction,where Ru SA acted as hydrogen evolution active sites and Ru O₂ nanoparticles promoted selective oxidation of benzyl alcohol and water dissociation,thereby significantly accelerating the selective oxidation of benzyl alcohol and hydrogen production.This study demonstrated a dual-function photocatalytic reaction through rational construction of photocatalytic active sites and revealed the synergistic catalytic mechanism of different active sites in the photocatalytic reactions,providing new insights for the development of efficient photocatalysts.2.Improving the photocatalytic performance by the modification of TiO₂ with non-precious metals is of great significance for reducing the cost of photocatalysts.The rational integration of semiconductor quantum dots（QDs）with TiO₂ nanostructures is a promising strategy to improve the photocatalytic performance.The Bi₂S₃QDs modified TiO₂（Bi₂S₃QD/TiO₂）photocatalyst was constructed by amino-assisted growth of Bi₂S₃QDs on the flower-like TiO₂ nanostructures which were synthesized via a solvothermal process.The introduction of Bi₂S₃ QDs on TiO₂ nanostructures not only enhanced the photoabsorption and photogenerated charge separation efficiency but also afforded the powerful photogenerated charge carriers and abundant active sites for photocatalytic reaction.The Bi₂S₃QD/TiO₂ photocatalyst exhibited a high performance in the redox-coupling reaction of H₂evolution and oxidative transformation of benzyl alcohol,achieving the production rates of H₂ up to 4.75 mmol·g_cat^-1·h^-1 and benzaldehyde up to6.12 mmol·g_cat^-1·h^-1,respectively,and also showed an excellent stability in the long-term photocatalytic reaction.Based on the detailed characterizations and experimental results,the photocatalytic mechanism following S-scheme heterojunction was proposed.Moreover,a trace amount of water in the reaction system could act as a promoter to further accelerate the photocatalytic reaction.This work has some guiding significance for the rational construction of efficient and cost-effective photocatalysts to achieve the conversion of solar to chemical energy.