2D Titanium Oxide Surface Structure Control And Its Photocatalytic Performance

Energy is the material basis for human survival and an important material guarantee for the sustainable development of society and economy.Nowadays,the problem of energy consumption and environmental pollution is becoming increasingly serious.Photocatalytic technology with the advantages of low energy consumption,high efficiency and no secondary pollution,provides a new research method and idea for the development of new energy and environmental governance in the future.Researchers have been committed to the use of solar energy to the water splitting,solar power generation,solar energy reduction of greenhouse gas CO₂,solar energy organic synthesis and solar energy degradation of pollutants.Semiconductor materials as photocatalysts are a powerful medium for converting solar energy into chemical energy.TiO₂ is one of the most concerned semiconductor materials with the above applications.However,TiO₂ has a wide band gap?generally,the anatase phase is about 3.2 eV?,which is conducive to absorbing only ultraviolet light?It accounts for about 5%of the total spectrum?.At the same time,the electron hole pairs cannot be effectively separated,so the photocatalytic activity is limited to some extent.Therefore,we hope to use the electronic and physicochemical properties of two-dimensional?2D?lamellar structure to regulate the surface structure of 2D TiO₂,thereby changing its electronic structure and further improving its photocatalytic water splitting performance.?1?Assembly of TiO₂ ultrathin nanosheets with surface lattice distortion and atomic thickness was synthesized by gas-assisted liquid exfoliation and high-temperature surface hydrogenation method.It achieves super-large specific surface area(340 m²g^-1)and provides a large number of surface-active sites for photocatalytic reactions.Assembly of TiO₂ ultrathin nanosheets possesses a high proportion of low coordinated surface atoms and uniform oxygen vacancies,which can cause surface lattice distortion and change its electronic structure?resulting in a decrease of band gap and an upward shift of the bottom of the conduction band?.Simultaneously,it can increase the absorption of photons,effectively separate the electron hole pairs,and further accelerate the photocatalytic reaction process.Therefore,assembly of ultrathin nanosheets has excellent photocatalytic hydrogen production performance under visible light irradiation.?2?The titanate nanosheets were prepared by a simple solvothermal method as precursor,and then 2D anatase phase ultrathin TiO₂ nanosheets with bulk and surface void defects were obtained by air heat treatment technology.Under the condition of simulated sunlight?AM1.5?and chloroplatinic acid as a cocatalyst,the catalyst can split water to hydrogen and oxygen.This work made it possible for anatase phase TiO₂ to split pure water to produce hydrogen and oxygen,and further studied the reaction path of the splitting pure water,and found that it was mainly two consecutive two-electron processes,which proves the existence of the intermediate product H₂O₂.In addition,a large number of surface unsaturated dangling bonds and voids defects can serve as active sites for oxygen generation,and it is beneficial to the adsorption and desorption of hydroxyl groups in water,further promoting water splitting.?3?The MoS₂ nanosheet/TiO₂ ultrathin nanosheet heterostructure?MoS₂/TiO₂?was prepared by solvent thermal and secondary hydrothermal method.The two-dimensional material stacking structure of long sheets on the chip can split pure water and generate hydrogen evolution reaction under simulated sunlight under AM1.5 light source.The MoS₂/TiO₂ heterostructure composite changes its own electronic structure,leading to the extending the photoresponse range to the visible regions.In addition to the electronic structure characteristics of two-dimensional materials,the strong electron-attracting ability of MoS₂,the synergistic effect of MoS₂/TiO₂ heterojunction and the close contact between interfaces effectively improve the separation efficiency of photogenerated electron hole pairs.The results show that MoS₂/TiO₂ heterojunction can photocatalytically split pure water without any co-catalyst or sacrificial agent.