Preparation And Photocatalytic Properties Of BiOX-based Photocatalysts

Recently,along with the increasingly concern about the shortage of energy and the pollution of the environment,environment pollution treatment technology and new energy technology have become one of research hotspot.The semiconductor photocatalytic technology exhibits considerable potential applications in the conversion of solar energy and environment problems,and has attracted much attention.In the past forty years,conventional photocatalysts,such as Titania?TiO2?and Zinc Oxide?ZnO?,have attracted great interest and been widely studied,due to easy availability,low-cost,nontoxicity and high photostability.However,these conventional photocatalysts can only responde to ultraviolet light because of their wide band gaps,which lead to the low utilization of solar energy.Moreover,the quantum efficiency is low,because of a low efficiency of photoinduced charges separation,which limit the improvement of photocatalytic performance.To solve above-mentioned problems,world-wide researchers have to work hard to develope visible-light-driven photocatalyst.Bismuth oxyhalides?Bi OX?,as a p-type semiconductor with special energy band structure,show unique electronic and optical properties.In the BiOX structure,internal electronic field induced by the unique layered structure favors the separation of photogenerated carriers.All those indicate that BiOX has a good potential application in photocatalysis.At present,various methods have been reported for the preparation of BiOX,such as hydrolysis,hydrothermal and solvothermal methods.But these methods are complicated and require strict conditions.Moreover,its low quantum efficiency greatly decreases its photoactivity and leads to poor utilization of solar light.To resolve the aforementioned issues and enhance its photocatalytic activities,herein,a series of BiOX/semiconductor composite photocatalysts were synthesized though combustion method and acid treating method.The main contents of the thesis are as follows:?1?Magnetic NiFe₂O₄/BiOBr composite photocatalysts were synthesized by a simple combustion method.Due to suitable band structures of NiFe₂O₄ and BiOBr,the NiFe₂O₄/BiOBr heterojunction can promote the separation of photogenerated electrons and holes,which enhances the photocatalytic performance significantly.Moreover,due to the magnetic properties of NiFe₂O₄,as-synthesized NiFe₂O₄/BiOBr composites can be collected under an external magnetic field.?2?BiVO₄/BiOCl composite photocatalysts were synthesized by a one-pot combustion method.Monoclinic BiVO₄ with small band gap can harvest visible light.With the help of sensitization of BiVO₄,BiVO₄/BiOCl photocatalysts show improved visible light harvesting than pure BiOCl,resulting in more effective utilization of solar light.Moreover,the heterojunction of BiVO₄/BiOCl results in enhanced photocatalytic performance for RhB through promoting the separation of photogenerated charges.?3?BiOBr/Bi₂Sn₂O₇ heterojunction photocatalysts were successfully synthesized through HBr treating hydrothermal Bi₂Sn₂O₇ nanoparticles.During the HBr treatment,partial Bi₂Sn₂O₇ nanoparticles reacted with HBr acid to form the sheet-like BiOBr,the BiOBr/Bi₂Sn₂O₇ heterojunction was obtained.Through changing the HBr concentration,BiOBr/Bi₂Sn₂O₇ photocatalysts with various weight ratios of BiOBr to Bi₂Sn₂O₇ were prepared.In the composites,the interface between BiOBr and Bi₂Sn₂O₇ is close.The close interface facilitates the transfer of photoinduced charges and hampers the recombination of electrons and holes,which results in the enhanced photocatalytic activities.?4?BiOCl/Bi₂Sn₂O₇ composite photocatalysts were synthesized through the treatment of Bi₂Sn₂O₇ with HCl solution.Due to the sensitization effects of Bi₂Sn₂O₇,BiOCl/Bi₂Sn₂O₇ composites can respond to visible light.Through the synergetic effects of heterojunction and the special microstructure,the utilization of sunlight and photoactivity are enhanced.