Low Defect Light Absorbing Mixed Metal Oxide Semiconductor Material Study On Preparation And Photocatalytic Activity

Nowadays,how to use solar energy to promote water splitting is highly concerned,and the key to use of sunlight effectively is developing a photocatalyst that can respond to visible light.The crystal defects of photocatalysts in the visible spectrum are often used as recombination centers of photogenerated electrons and holes,high crystallinity and low defect absorbing by reducing the recombination of photogenerated electrons and holes improve the photocatalytic activity.Therefore,it is deserved to develope lower defect absorption and higher crystallinity photocatalysts.Metal oxynitride LaTi O₂N and metal oxynitride SrNbO₂N prepared via themal ammonalysis of La₂TiO₅ and Sr₅Nb₄O₁₅,Sr₄Nb₂O₉ were firstly synthesied successfully,which solved the above questions effectively,after a follow-up activity optimization?annealing treatment?,making metal oxynitrides achieve photocatalytic oxidation of water.Firstly,in this experiment,it adopted two-step method to prepare metal oxynitrides LaTiO₂N,La₂Ti₂O₇ and La₂TiO₅ were prepared by NaCl-KCl flux growth method.Subsequently,these oxides were converted to metal oxynitrides LaTiO2N via thermal ammonolysis.So far,only La₂Ti₂O₇ by molten salt prepared had been reported.Though LaTiO2N prepared from La2TiO5 appeared almost no defect absorption in UV-Vis-NIR and electron paramagnetic resonance spectroscopies,its performance was significantly lower than that of the traditional LaTiO2N derived from La2Ti2O7.As was shown by Mott-Schottky analysis,comparing with La₂Ti₂O₇-derived LaTiO₂N,La₂TiO₅-derived LaTiO₂N had a significantly lower donor density,this may lead to the separation of photogenerated electrons and holes in the built electric field.The lower donor density was also consistent with the small difference between the Fermi energy and the maximum of the valence band,which indicated La₂TiO₅-derived LaTiO₂N had a lower oxidative power of the hole.Next,Sr₂Nb₂O₇,Sr₅Nb₄O₁₅,Sr₄Nb₂O₉ were prepared by NaCl-KCl flux growth method.Subsequently,these oxides are converted to metal oxynitrides SrNbO₂N via thermal ammonolysis.So far,only Sr₂Nb₂O₇ by molten salt prepared had been reported.In similar with La₂TiO₅-derived LaTiO₂N,Sr₅Nb₄O₁₅-derived SrNbO₂N exhibited lower defect absorption.As was shown by Mott-Schottky analysis,Sr₅Nb₄O₁₅-derived SrNbO₂N performed much lower donor density,this may resulted in the separation of photogenerated electrons and holes in the built electric field.The lower donor density was also consistent with the small difference between the Fermi energy and the maximum of the valence band,which showed that Sr₅Nb₄O₁₅-derived SrNbO₂N had a lower oxidative power of the hole.Increasing donor density was conducive to improve the photocatalytic activity,after Ar annealing,the donor density of Sr₅Nb₄O₁₅-derived SrNbO₂N is higher,thus improving the photocatalytic activity,which was never been reported.SrNbO2N-f.5415 had the highest photocatalytic activity after 700°C annealing treatment,which was instructive in the field of photocatalysis.In addition,photocatalytic activity of SrNbO₂N-f.5415 can be improved by loading CoOx as a co-catalyst.