The Synthesis Of Bi₁₂TiO₂₀ And Bi₁₂TiO₂₀/g-C₃N₄ And Their Visible Light Photocatalytic Performance Toward Organic Pollutants

Recently,the sillenite Bi₁₂TiO₂₀,as a new-type photocatalyst,has attracted great attention owing to its unique structure and excellent visible-light response ability.However,researches related to morphology（crystal exposure）control synthesis,facet-dependent photocatalytic performance as well as theoretical calculations still need further study.Therefore,the control synthesis of special facet exposed Bi₁₂TiO₂₀（{111}crystal）was selected as a key research point to study the{111}facet-dependent photocatalytic performance.At the same time,the crystal electronic structure,surface energy,band structure and density of states were deeply investigated based on the first principles theories,which were beneficial to analyze the proposed formation and photocatalytic mechanism of Bi₁₂TiO₂₀ tetrahedrons.In addition,based on the matching principle of band structure,the study focused on the synthesis of Bi₁₂TiO₂₀/g-C₃N₄ composite and the effects of interface and band structure on its photocatalytic performance.The main researches are as follows:100%{111}crystal exposed Bi₁₂TiO₂₀ tetrahedrons with size around 3μm were prepared by hydrothermal method.Specifically,TiO₂ and Bi₂O₃ were used to be raw materials and the prepared precursor was treated by 220℃for 0.5 h.It can be found that solution alkalinity and reaction time have important effects on the formation of the tetrahedral Bi₁₂TiO₂₀.And with the increase of hydrothermal time,Bi₁₂TiO₂₀polyhedrons with the high index facets exposed can be prepared.Furthermore,the calculations based on first principles thories showed that{111}facet has the highest surface energy among three low index facets.Bi₁₂TiO₂₀ tetrahedrons have relatively good photocatalytic oxidation and reduction performance,mainly because{111}facet is the most active facet,and Bi₁₂TiO₂₀ has unique electronic structure units as well as excellent visible light response abilityBi12TiO20/g-C3N4 composite with facet-coupled structure was successfully synthesized by ultrasonic treatment under 59KHz for 6 hours.The facet coupling structure existed between Bi₁₂TiO₂₀-{111}facet and g-C₃N₄-{002}facet.And the facet coupled structure got enhanced through covalent bonds Ti-N and Ti-O-C.According to the investigation of the photocatalytic mechanism of Bi₁₂TiO₂₀/g-C₃N₄,the band structure of{111}facet exposed Bi₁₂TiO₂₀ and{002}facet exposed g-C₃N₄matched well with each other after thermodynamic equilibrium,forming a stable staggered band alignment structure,which can effectively separate the photo induced charges and boost the photocatalytic performance.The work provide the theoretical basis for the control synthesis of photocatalysts and their facet dependent photocatalytic activity.