Study On Synthesis And Photocatalytic Performance Of TiO₂ Modified With Fluorine

TiO₂ has been favored by researchers due to its unique physical and chemical properties such as cheap,non-toxic,good thermal stability and so on.However,the low light utilization efficiency and high recombination rate of photogenerated carriers limit its application in practice.Therefore,the keys to improve the photocatalytic activity of TiO₂ are narrow its band gap and prolong the charge lifetime.In view of the above two points,in this paper,the method of surface fluorination is used to adjust the band structure,electron migration and surface chemistry properties of TiO₂ to improve its photocatalytic activity.The corresponding investigations were mainly focused on the following aspects:1.When tetrabutyl titanate and pentafluoropyridine were as raw materials,C-N-F co-doped TiO₂ was successfully prepared by hydrothermal and different atmosphere heat treatment methods.Various characterization analyses were performed on the samples,and the visible light photocatalytic activity of the prepared samples was tested by degrading phenol under visible light.Carbonized C-N-F co-doped TiO₂ in a micro-oxygen atmosphere will cover the surface with carbonaceous substances with carboxyl groups.Nitrogen doping can introduce impurity levels in the forbidden band,shorten the forbidden band width,and enable TiO₂ to respond to visible light.Fluoride ions form surface modifications in the form of CF bonds.The synergistic effect of surface carboxyl groups and fluoride ions will reduce the position of the TiO₂ valence band edge,and at the same time will attract electrons to migrate to the surface,reducing the recombination rate of photogenerated carriers.When the three elements of C,N,and F are co-doped,the synergy of the three elements can shorten the band gap of TiO₂,expand the light response range,reduce the position of the valence band edge,and inhibit the recombination of electron-hole pairs,which significantly enhances the oxidation ability of holes,improves the photocatalytic activity of TiO₂ for degradation of phenol under visible light.2.The oxygen vacancy defect TiO₂ was prepared by precipitation method.Then,the oxygen vacancy defect TiO₂ was subjected to surface fluorination treatment to prepare the surface fluorinated oxygen defect TiO₂.The structure and morphology,surface chemical state,band structure and photogenerated charge carrier dynamics of the sample were analyzed in detail by a series of characterizations.The photocatalytic activity of the samples was tested by degrading phenol under ultraviolet light.The result shows that surface fluorination treatment will change the types of TiO₂ surface active adsorption species and surface chemical properties.The oxygen vacancy defects in the surface fluorinated TiO₂ can not only contribute to the TiO₂ valence band side impurity level,form a valence band tail state,shorten the band gap,but also provide electrons.The electron-withdrawing effect of surface fluoride ions will accelerate the migration of electrons to the surface and reduce the recombination rate of electrons and holes.The synergistic effect of oxygen vacancy defects and fluoride ions reduces the band gap of TiO₂,improves the separation efficiency of photogenerated carriers and the redox ability of TiO₂,which exhibits good photocatalytic activity during the degradation of phenol.