Modification Of Semiconductor Photocatalytic Materials For BiVO₄ And TiO₂ With Enhanced Photoreactivity

Photocatalytic technology has been attracted much attention due to its potential to solve the problems of energy shortage and environmental pollution caused by the rapid development of economy.TiO₂ and BiVO₄ are considered as the representative UV-and visible-light responsive photocatalysts,respectively.However,the quantum efficiencies of TiO2 and BiVO4 photocatalysis are low due to the quick recombination rate of photo-generated electron-hole pairs.In this thesis,we tried to improve the photocatalytic activity of TiO2 and BiVO4 by improving the separating the photo-generated carriers through the strategies of surface modification and semiconductor coupling.The details of the study are as follows:?1?Fabricationofwalnut-likecore-shellstructuredBiVO₄@Bi₂S₃heterojunction.Walnut-like core-shell structured BiVO₄@Bi₂S₃ heterojunction was prepared by depositing a layer of Bi₂S₃ on the surface of BiVO₄ by in-situ transformation of BiVO₄ into Bi₂S₃ via hydrothermal reaction in the presenc of Na₂S·9H₂O.We systematically studied the effect of Na₂S·9H₂O amount on the structure and photocatalytic activity of BiVO₄@Bi₂S₃ heterojunction.It was found that S3 sample,prepared at the weight ratio of Na₂S·9H₂O:BiVO₄=3:1,shows the highest activity in photoreduction of Cr?VI?in solution,which is 57.2 times higher than pristine BiVO₄.The enhanced photocatalytic activity of BiVO₄@Bi₂S₃ was attributed to the increased light-harvesting ability due to the photosensitization of Bi2S3 layer and efficient seperation of photo-generated carriers due to the semiconductor-coupling effect between BiVO₄ and Bi₂S_3.?2?Surface fluorination of TiO₂ nanocrystals.Anatase TiO₂ nanocrystals were prepared by calcination of TiOF₂ precursor,a kind of fluorine-containing materials.T3 sample that was calcined at 300 ^oC mainly shows TiOF₂ phase.However,T4sample that was calcined at 400 ^oC is the mixture of anatase TiO₂ and TiOF₂ due to the heat-induced phase transformation.Pure anatase TiO₂ was obtained for T5 sample that was calcined at 500 ^oC,reflecting the completion of TiOF₂-to-TiO₂ phase transformation.T4 sample shows the highest photoreactivity in oxidation of acetone,a typical VOCs.Because TiOF₂ was reported to exihibit very poor photoreactivity,the enhanced photocatalytic activity of T4 sample is attributed to the surface fluorination effect,which facilitates the oxidation of acetone by holes due to the fact that photo-generated electons are trapped by surface bound fluoride ions.