Research Of Carrier Kinetic Behavior In Vacancy Oxygen-doped TiO₂ Photocatalytic Hydrogen Generation By AC Disturbance Methods

Looking for environmentally friendly and renewable energy sources to replace traditional fossil energy sources has become the focus of many scientific researchers owing to increasingly depleted fossil energy sources and serious environmental contamination.Hydrogen,as a clean sustainable energy source,is unanimously concerned as the most ideal alternative energy carrier.Oxygen vacancy（V_O）doped TiO₂ has attracted wide attention owing to its excellent light absorption and hydrogen generation activity.However,the role of V_O in TiO₂ photocatalysts is controversial,and its kinetics need to be further analyzed.The transfer and recombination rates of carriers can be calculated quantitatively by AC perturbation methods such as intensity modulated photocurrent spectroscopy（IMPS）and photochemical impedance spectroscopy（PEIS）,which can effectively analyze the mechanism of V_O in photocatalytic reactions,so as to further improve its photocatalytic performance.Herein,the photoinduced carrier behavior of V_O-doped TiO₂ nanotubes was researched using IMPS and PEIS,which provided a complete description of the photochemical properties of TiO₂ nanotubes,clarified the different effects of different separate V_O on the photocatalytic properties,and further improved the photocatalytic hydrogen generetion performance of TiO₂ nanotubes using organic hole transport materials.The specific research contents are as follows:（1）The V_O self-doped TiO₂ nanotube film photocatalyst was prepared by anodization and aluminum thermal reduction.Subsequently,the IMPS and PEIS were used to research the photoelectrode carrier transport mechanism,the photocatalytic kinetic models were established,and the mechanism of the influence of different distribution of V_O on the photocatalytic performance of TiO₂ was clarified.The results show that surface V_O improves photocatalytic performance by improving the separation efficiency of photoinduced carriers,while bulk V_O as a recombination center does harm to photocatalytic performance.In addition,the low interfacial charge transfer efficiency caused by surface V_O limits further improvement in the photocatalytic hydroproduction properties of materials.（2）In order to further improve the photocatalytic activity of the surface V_O-doped TiO₂nanotubes（TNT-S）,a modification method for the adsorption of hole transport material on the TNT-S surface is proposed.L1 or 2m F-X59 coatings with different thicknesses were loaded on the TNT-S surface by one-step spin coating method.The effects of coating thickness and organic molecular properties on the interface charge transfer efficiency and optical absorption efficiency of TNT-S were studied.And the kinetics of photocatalytic performance improvement was revealed combined with kinetic experiments（IMPS et al.）and density functional theory calculations.The results indicate that the built-in field between the organic hole transport coating and TNT-S promotes the directional transport of the current carriers,and the fluorinated group is the reason of the higher intensity built-in field of TNT-S/F-X59.In addition,too thick coating will also reduce the photocatalytic hydrogen production efficiency owing to reducing the photoabsorption efficiency of the material.Finally,the best modification effect is achieved when rotary coating 4 layers of 2m F-X59,of which hydrogen generation efficiency reaches2.706 mmol g^-1 h^-1 under visible light.