Study On Modification Of TaON And Properties Of Photocatalytic Hydrogen Production

With the rapid development of social economy and industrial technology,photocatalytic technology has attracted the attention of more and more scholars due to its simple,cheap,and non-polluting characteristics.TaON as a single metal oxynitride,due to its narrow energy band structure for absorbing visible light and good chemical stability,high theoretical solar hydrogen conversion efficiency,abundant reserves,simple preparation process,has been used as a new type of photocatalyst with excellent performance.It is widely used in scientific fields such as water splitting,pollutant degradation,and organic compound catalytic synthesis.However,TaON also has shortcomings such as low internal quantum efficiency,insufficient surface active sites,and rapid recombination of photogenerated electrons and holes,resulting in unsatisfactory photocatalytic activity.Modification strategies for improving its photocatalytic activity are constantly being studied to improve its actual solar-hydrogen conversion efficiency.Firstly,TaON was subjected to aluminothermic reduction treatment to prepare ordered-disordered TaON homogeneous junction particles to enhance its photocatalytic activity in this thesis.Secondly,regular TaON nanotubes were prepared by anodizing and nitriding method,while changing the morphology of the TaON nanotube array,increasing the specific surface area and changing the internal stress between the nanotubes and between the nanotubes and the metal substrate finally achieves the purpose of enhancing the photocatalytic activity of TaON.（1）The ordered-disordered TaON homojunction photocatalysts with different concentrations of surface oxygen vacancies were prepared by a simple and novel aluminothermic reduction method.The morphology,structure and photoelectrochemical properties of the TaON homojunction photocatalysts were characterized by SEM,XRD,UV-vis,photoelectrochemical and other characterization methods.The results show that surface oxygen vacancy defects destroy the periodicity of the crystal surface and weaken the crystallinity of TaON particles,resulting in the crystal core and amorphous shell structure.The introduction of oxygen vacancies plays a key role in adjusting the band structure and charge dynamics of TaON.Not only will there be a defect energy level in the forbidden band,which greatly expands and enhances the light absorption range of TaON particles,but also forms an ordered-disordered TaON homojunction,thereby increasing the concentration of photogenerated carriers,suppressing the photo-generated charge recombines and promotes effective surface photocatalytic reaction,significantly improving the photocatalytic hydrogen production activity of the TaON photocatalyst.The aluminothermic reduction temperature of the best TaON photocatalytic activity is 400℃,and the hydrogen production activity is 25μmol g^-1h^-1,which is about twice that of pure TaON under visible light.（2）The regular TaON nanotube arrays were prepared by a simple anodization and nitriding method.The morphology,structure,photoelectrochemical properties and the formation mechanism of the TaON nanotube array were characterized by SEM,XRD,UV-vis,photoelectrochemical and other characterization methods.The photoelectrocatalytic splitting water performance of TaON nanotube array was evaluated under visible light irradiation by controlling the anodic oxidation time to adjust the morphology of the nanotubes and the difference in the internal stress between the nanotubes and between the nanotubes and the metal substrate.The results show that the nanotubes anodized for 10 min have the most regular morphological structure,the highest carrier concentration,the narrowest thickness of the space charge layer and the best photoelectrocatalytic activity.The photoelectrocatalytic hydrogen production rate can reach 8μmol cm^-2h^-1at 1.23 V vs.RHE under visible light.Correspondingly,owing to its increased specific surface area,regular nanotube structure and smaller internal stress between the nanotubes and between the nanotubes and the metal substrate,which brings more reactive sites and rapid carrier separation and transport,and effectively promotes the adsorption and dissociation of H₂O molecules,this ultimately leads to enhanced photoelectrocatalytic activity.