The Preparation Of Oxygen Vacancy Doped TiO₂ And The Research In Photocatalytic Reduction Of CO₂

Titanium dioxide?TiO₂?,which is widely used as a catalyst in degradation of pollutant substance and solar energy conversion,has been identified as one of the most promising photocatalytic material,based on it is strong oxidizing property,non-toxic,long term stability,low cost,high catalytic activity etc.However,as a photocatalyst,TiO₂ suffers from low solar energy conversion efficiency and excessive electron-hole recombination,which leads to it is not greatly applied in the photocatalyst.Therefor,various strategies such as coupling with other semiconductors,noble metals loading,dye sensitization and doping have been developed recently to alleviate these limitations.Among these strategies,doping of TiO₂ including metal ion doping,nonmetal doping,and self-doped has been widely invesitigated.Self-doped TiO₂ involes Ti3+ and oxygen vacancies doping.In this paper,three different kinds of TiO₂ nanomaterials have been designed and fabricated by dehydration of nanotube titanic acid?NTA?and reduction of anatase TiO₂ by Na BH4.In addition,the ratio of the surface oxygen vacancies and bulk SETOVs was adjusted through some strategies.All the TiO₂ nanomaterisls photocatalyst were investigated by photoreduction of CO2 experiment.Details are as following:?1?We designed and fabricated three different TiO₂ nanomaterials with surface oxygen vacancies and/or bulk SETOVs successfully.TiO₂ with bulk SETOVs was obtained by dehydration of nanotube titanic acid?NTA?and the sample with surface oxygen vacancy was synthesized through reduction of anatase TiO₂ by Na BH4,while the last one with both surface and bulk oxygen vacancy was prepared by reduction of novel TiO₂ by Na BH4.The three kinds of TiO₂ nanoparticles were characterized systematically by ESR,XPS,TG,TEM and Raman techniques.The production rate of CH4 on the common anatase TiO₂ raw was 10.30 ppm?g-1h-1,we found that the highest activity of 235.24 ppm?g-1h-1 without loading anynoble metal was obtained by the one with both surface and bulk oxygen vacancy.The photocatalytic reduction results of CO2 indicated that both the bulk SETOVs and surface oxygen vacancies contributed to the enhancement of the light absorption,while the surface vacancies facilitated to the separation of the photo-generated charge carriers,and on the contrast,the bulk SETOVs acted as the recombination center.The coexistence of the surface and bulk oxygen vacancies exhibited a synergistic effect to improve the photoreduction efficiency.?2?Three samples with different ratio of surface oxygen vacancy and bulk SETOV were synthesized by calcining NTA in 400 oC,500 oC and 600 oC.In this process,we make sure the concentration of bulk oxygen vacancies changing while the surface oxygen vacancies unchanged.The three kinds of samples were characterized by Positron annihilation techniques,the ratio of I1 to I2?I1/I2?for TiO₂-SBO-400,TiO₂-SBO-500,TiO₂-SBO-600 were 2.635,4.825,and 8.347 respectively,indicating that the ratio of bulk defects to surface defects increases with the improvement of the dehydration temperature of NTA.But the highest production rate of CH4 was TiO₂-SBO-400.Combined with other characterization,we found the activity of photocatalytic reduction of CO2 on these samples were different.The conclusion is that the photocatalytic activity of TiO₂ photocatalyst will be enhanced by increasing the ratio of surface oxygen vacancies and bulk oxygen vacancies.?3?Three kinds of samples were synthesized through reduction of anatase TiO2 by Al thermal reduction.These samples contain bulk oxygen vacancies,surface oxygen vacancies,and bulk and surface oxygen vacancies coexisted respectively.We found the concentration of oxygen vacancies in TiO₂ is different by Na BH4 reduction and Al thermal reduction.With the method of Al thermal reduction,the concentration of bulk oxygen vacancy is relatively high while the surface oxygen vacancy concentration is low.The production rate of CH4 on A-TiO₂-SBO-10 h was 37.12ppm?g-1h-1,which was much lower than that of TiO₂-SBO.The photocatalytic activity of TiO₂ photocatalyst was effected by the concentration of oxygen vacancy and the ratio of surface oxygen vacancies and bulk oxygen vacancies.The photoreduction efficiency of CO2 on TiO₂ will be improved by increasing the ratio of surface oxygen vacancies to bulk oxygen vacancies.