The Preparation Of Tantalum (Oxygen) Nitride And Visible Light Catalytic Performance For Hydrogen Production

The excessive use of non-renewable fossil energy has caused an energy crisis and severe environmental pollution,finding clean and sustainable energy is the key to solving the problem.Hydrogen energy is a chemical energy source with high combustion value,no secondary pollution,and no toxicity,the use of hydrogen energy instead of fossil energy will provide effective solutions for energy depletion and environmental pollution.The aim of this paper is to prepare a single semiconductor photocatalyst with hydrogen production performance under visible light irradiation.For the catalyst to have visible light catalytic hydrogen production activity,it must have visible light absorption capacity,and the separation efficiency of photogenerated carriers should be high.The band gap of Ta₃N₅ is 2.1 e V,which has visible light catalytic activity,but it is limited to use due to its high photogenerated carrier recombination rate,in this paper,the method of topology conversion is used to prepare Ta₃N₅ with a mesocrystal superstructure,the structure provides an effective path for the transport of photogenerated carriers,accelerates the separation of photogenerated carriers,and overcomes the problem of high photogenerated carrier recombination due to the narrow band gap;The band gap width of Ta₂O₅ is about 4.0 e V,because of the wide band gap,there is no visible light activity,in this paper,the solvothermal method is used to prepare Cl-Ta₂O₅-x,which has oxygen vacancy defects and Cl-doped amorphous microspheres,it has hydrogen production activity,which overcomes the problem of no visible light catalytic activity due to its wide band gap.The main contents of this paper are as follows:?1?Mesocrystal Ta₂O₅ was prepared by solvothermal method and calcination method,and then mesocrystal Ta₃N₅ was successfully prepared by calcination under the NH3 atmosphere in the tube furnace by topology conversion method,comm-Ta₃N₅ was prepared from commercial Ta₂O₅ by the same method of topological transformation,the catalytic hydrogen production of mesocrystal Ta₃N₅ nanosheets under visible light was investigated.The experimental results show that neither the mesocrystal Ta₂O₅ nor the commercial Ta₂O₅ has visible light catalytic hydrogen production activity,the mesocrystal Ta₃N₅ and the comm-Ta₃N₅ both have visible light catalytic hydrogen production activity,and the mesocrystal Ta₃N₅-850 nanosheets produces 5.28 times the hydrogen production of the comm-Ta₃N₅.The results of SEM and TEM showed that the mesocrystalline Ta₃N₅ was composed of nanoparticles and had an ordered nanosheets superstructure;Transient photocurrent response,electrochemical AC impedance spectroscopy,fluorescence emission spectroscopy,time-resolved fluorescence spectroscopy,et al.characteristics prove that ordered nanosheets superstructure provides an effective transmission path for photogenerated electrons and holes,reduces the charge transfer resistance and speeds up the transfer speed of photogenerated carriers,increase the carrier separation efficiency and the fluorescence lifetime of photogenerated carriers;The N₂ adsorption and desorption curve test results show that the mesocrystal Ta₃N₅-850 nanosheets has a high specific surface area and provides more active sites.?2?Using TaCl₅ as the precursor material and acetone as the solvent,the amorphous Cl-Ta₂O₅-x microspheres with oxygen vacancy defects and Cl doping were successfully prepared by solvothermal method,the catalytic hydrogen production performance of the amorphous Cl-Ta₂O₅-x microspheres under visible light irradiation was investigated.The results show that commercial Ta₂O₅ has no visible light catalytic hydrogen production performance,and amorphous Cl-Ta₂O₅-x microspheres has visible light catalytic activity under visible light irradiation,in which amorphous Cl-Ta₂O₅-x-200 microspheres produces hydrogen 56.96 ?mol g-1 within 180 minutes under visible light irradiation,which shows good visible light catalytic activity compared to commercial Ta₂O₅.From experiments such as investigating the hydrogen production stability of the catalyst,the influence of the catalyst quality on the hydrogen production performance,and the hydrogen production performance of the catalyst under different single wavelengths,it is concluded that amorphous Cl-Ta₂O₅-x microspheres has visible light catalytic hydrogen production performance.X-ray electron energy spectrum and electron paramagnetic resonance characterization prove that amorphous Cl-Ta₂O₅-x microspheres contains oxygen vacancy defects and Cl doping,ultraviolet-visible diffuse reflection absorption spectroscopy,time-resolved fluorescence spectroscopy,electrochemical AC impedance,et al.characteristics show that,oxygen vacancy defects and Cl doping increase the light absorption capacity of the amorphous Cl-Ta₂O₅-x microspheres,which broadens the absorption range to visible light,the transfer ability of photogenerated carriers and the separation efficiency of photogenerated carriers are increased,and the fluorescence lifetime of photogenerated carriers is increased.