Synthesis,Modification And Photocatalytic Properties Of Anatase TiO₂ With High Exposed（001） Facets

TiO₂ is the most widely studied photocatalyst by far,and plays an important role in the treatment of water pollution.The separation and transfer of photo-generated electrons and holes at the interface are the bottlenecks of the photocatalytic kinetics of TiO₂.As the research focus,appropriate regulation of crystal surface and defect introduction can change the band structure of the catalyst in a self-structure modification manner,and promote the separation and transfer of electrons and holes.Based on the control of crystal facets and defect introduction,we disscus the effect of ratio of F and Ti atoms on the exposure of TiO₂（001）crystal facets and the heat treatments under different atmospheric on the catalytic performance of TiO₂.The specific content is as follows:（1）TiO₂ exposed on the（001）crystal facets are prepared by hydrothermal method using tetrabutyl titanate as the titanium source and NaF and H2SO4 as crystal facets modifiers,and the effect of the ratio of F and Ti atoms on the structure evolution and photocatalytic performance is revealed.Our results show that the catalyst is spherical TiO₂ agglomerated by irregular particles without NaF.With the increases of the ratio,the TiO₂ evolves into hollow spheres agglomerated by small particles,and then transforms into a square structure with small stacks of layers.Finally,truncated octahedron structure stacked by large layer is formed,and the expoesion of（001）crystal plane increases from 14%to 60%.When the radio of F and Ti atoms is 0.17,the catalytic efficiency is three times that of TiO₂ without NaF.Although the specific surface area is reduced,the moderate exposure of the（001）crystal facets promotes the separation and transfer of electrons and holes,which showed strong photocurrent response,moreover,the holes has a stronger oxidizability with the positive shift of valence band,which is important for the degradation of dyes dominated by hole oxidation.（2）We chose TiO₂ modified with a moderate ratio of F and Ti atoms as the model catalyst to study the effect of heat treatment in air,nitrogen,and hydrogen atmospheres on its catalytic performance.After calcination,the Ti 2p peaks shifts toward the low binding energy,and the surface hydroxyl content is increased or decreased with different degrees.After air calcination,the adsorbed fluorine on the surface of TiO₂ is basically removed,and the crystallinity is enhanced.Under the conditions of nitrogen and hydrogen calcination,there are still partial fluorine adsorbed on the surface of the catalyst,and（001）and（101）crystal facets could be observed,while under the conditions of hydrogen calcination,there is a disordered layer around 4 nm on the surface of TiO₂.In addition,the flat band potentials of the three catalysts have different degrees of negative movement compared to the samples before calcination,and the band structure is also significantly different.After three types of post-treatment,the performance of the catalyst samples decreases in varying degrees due to the sintering of the crystals,while the performance difference under different atmospheres is attributed to the difference in the electron-hole separation efficiency,crystal defects and the valence band position of the catalysts.