Preparation And Photocatalytic Properties Of BiOX-based Composite Photocatalysts

In recent ten years,bismuth oxyhalide(BiOX)based photocatalysts have become one of the hottest photocatalysts due to their unique layered structure and indirect transition mode.However,there is still a big gap between its photocatalytic performance and the actual application.The current research is mainly focused on the laboratory setting.Photogenerated electrons and holes are the most important active species in the photocatalytic reaction process,and their number directly determines the photocatalytic performance of BiOX.Carrier yield is mainly affected by visible light capture efficiency and carrier separation efficiency.In view of the above two important factors affecting the photocatalytic activity,this dissertation proposed a solution of combining the two modification strategies of heterojunction and solid solution.The energy band structures of BiOX were optimized by using the idea of energy band engineering,and the visible light capture efficiency and carrier separation efficiency were improved to finally achieve the purpose of improving the photocatalytic activity.Meanwhile,the synergistic effect between the two modification methods was discussed.In addition,the powder catalyst was immobilized to alleviate the problems of difficult recovery and secondary pollution.The experimental results were instructive to the design of new photocatalytic materials.The main contents of this dissertation are as follows:(1)A series of TiO2-BiOBrxI1-x heterojunctions were synthesized via combination of the two modification strategies of heterojunction and solid solution.The tightly bonded interface TiO2 nanorods(TiO2 NRs)and BiOBrxI1-x microspheres promoted the separation of carriers.At the same time,the band gaps of BiOBrxI1-x solid solutions were continuously adjusted in the range of 2.80 to 1.70 eV by adjusting the ratio of Br and I.TiO2-BiOBr0.75I0.25 exhibited the highest photocatalytic activity,which could be attributed to that the synergistic effect between the two modification strategies enabled it to have expanded light absorption range,optimized redox potential and fast carrier separation rate.(2)In order to break through the limitation of photocatalytic activity of traditional type Ⅱheterojunction,g-C3N4-BiOClxBr1-x direct Z-type heterojunctions were prepared by compounding graphitic carbon nitride(g-C3N4)and BiOClxBr1-x solid solutions by solvothermal method.At the same time,energy band structures of samples were optimized by the idea of energy band engineering.Among all g-C3N4-BiOClxBr1-x heterojunctions,the sample with x=0.5 had the highest photocatalytic activity,which was higher than that of pure g-C3N4 and BiOClxBr1-x,verifying the synergistic effect between the two modification methods.Finally,the heterojunction type and photocatalytic activity enhancement mechanism of samples were confirmed by a series of physical and chemical characterization.(3)Rutile TiO2 NRs arrays were grown on fluorine doped tin dioxide conductive glass(FTO)by hydrothermal method.The morphology of TiO2 NRs arrays was optimized by adjusting the synthesis conditions,and BiOX was immobilized by successive ionic layer absorption and reaction(SILAR).Photocatalytic degradation experiment of rhodamine B(RhB)showed that the apparent rate constant of BiOBr/TiO2/FTO with 4 cycles was 0.0104 min-1,which was 2.89 times of TiO2 NRs arrays.In addition,the photocatalytic properties of samples showed a significant correlation with the types of BiOX.BiOI/TiO2/FTO had the highest photocatalytic activity,which was mainly due to its strongest photo response.