Controllable Prepartion And Properties Of Bismuth-Based Heterojunction Photocatalyst

In recent years,the acceleration of industrialization and the rapid growth of population have led to the worldwide environmental pollution.Photocatalytic technology is green,simple operation,energy saving and not easy to produce secondary pollution.It is an ideal solution to human environmental problems,which can directly use solar energy to completely mineralize organic pollutants.Bismuth-based compounds have unique electronic structure and excellent light absorption properties.Combined with China's rich bismuth resources,research and development of high activity visible light bismuth-based photocatalyst has become a research hotspot in the field of photocatalysis.However,the bismuth-based photocatalyst still have the following challenges in practical applications:(i)Lower utilization rate of visible light;(ii)The migration and separation of photogenerated electrons and holes are inefficient.In order to solve the above problems,four bismuth-based photocatalyst were synthesized by constructing p-n,n-n heterojunctions,introduction of surface oxygen vacancies and dye sensitization.In this paper,the controllable preparation and characterization of photocatalysts,the photocatalyst properties of four bismuth-based photocatalyst,the relationship between the structure and photocatalytic activity,the effects of heterojunction,surface oxygen vacancies and dye sensitization on the migration and separation efficiency of photogenerated carriers at the interface during photocatalytic reaction were discussed in detail.The main research contents and achievements are given as follows:(1)The synthesis and characterization of hierarchical flower structure Co3O4/Bi2O2CO3 p-n heterojunction photocatalyst.Using citric acid as carbon source and directing agent,the hierarchical flower structure Bi2O2CO3 was prepared by hydrothermal method.Then,the Co3O4 nanoparticles were uniformly coated on Bi2O2CO3 by hydrothermal method to prepare Co3O4/Bi2O2CO3 composite photocatalyst.Combined with the results of photocatalysis experiments,we canconclude that Co3O4/Bi2O2CO3 shows excellent photocatalytic activity when the content of Co3O4 is 0.6 wt%.Under simulated visible light irradiation,90% MO is photodegraded after irradiated for 120 min.Photoelectric and ESR tests show that the hierarchical flower structure of the Co3O4/Bi2O2CO3 photocatalyst is beneficial to the absorption of visible light.Meanwhile,the p-n heterojunction formed between Co3O4 and Bi2O2CO3 effectively promotes the separation of the photogenerated electrons and holes.(2)The synthesis and characterization of solar light-driven Ce O2/Bi2O2CO3 type II n-n heterojunction photocatalyst.In this work,a novel Ce O2/Bi2O2CO3 heterojunction photocatalyst with hierarchical flower structure was synthesized by hydrothermal method.Combined with the results of photocatalysis experiments,we can conclude that Ce O2/Bi2O2CO3 shows excellent photocatalytic activity when the content of Ce O2 is 15 wt%.Under simulated solar light irradiation,98% MB is photodegraded after irradiated for 120 min.Combined with the results of photoelectric analysis,the photocatalytic mechanism of CB-15 composite photocatalyst was discussed.Good bandgap matching and coordination between Ce O2 and Bi2O2CO3 efficiently promote the separation of photogenerated electrons and holes.(3)In order to further improve the practical application of Bi2O2CO3 photocatalyst.Based on the Bi2O2CO3 hierarchical flower structure prepared in the first part,we synthesized core-shell structure by coating the Cd WO4 nanorods on the Bi2O2CO3 microsphere.Due to the characteristics of Cd WO4,surface oxygen vacancies were successfully introduced into the Cd WO4/Bi2O2CO3 composite.Under simulated solar light irradiation,99% Rh B,98% MB,62% MO,63% phenol are photodegraded after irradiated for 120 min.The TOC remove efficiency in each system is 92.3%,81.9%,81.2%,and 83.2%,respectively.By comparing the photocatalytic and photoelectric properties of oxygen vacancies-riched Cd WO4/Bi2O2CO3 composite with Bi2O2CO3,the superior properties of Cd WO4/Bi2O2CO3 composite are mainly attributed to the following three reasons are as follows(i)The introduction of surface oxygen vacancies leads to the formation of defect levels in the Cd WO4 band gap,which promotes the absorption of visible light.(ii)The interaction of the core-shell heterostructure interface can effectively improve separation of the photogenerated electrons and holes.(iii)The n-n heterojunction formed between Cd WO4 and Bi2O2CO3 further enhances the separation of photogenerated electrons and holes.(4)Controllable synthesis of a flower-like Cd WO4-Bi OCl-Bi2WO6 ternary hybrid photocatalyst with enhanced photocatalytic activity.Because of the structural transformation relationship between Bi OCl and Bi2WO6,we synthesized Cd WO4-Bi OCl-Bi2WO6 ternary hybrid photocatalyst via a one-pot hydrothermal method using the same raw materials with different molar ratios in the same system.Combined with the results of photocatalysis experiments,we can conclude that Cd WO4-Bi OCl-Bi2WO6 ternary hybrid photocatalyst shows excellent photocatalytic activity when the molar ratio of Cd to Bi is 0.05.Under simulated solar light irradiation,100% Rh B is photodegraded after irradiated for 120 min.Combined with the results of radical trapping experiments and photoelectric analysis,the photocatalytic mechanism of CBB-0.05 was discussed.The sensitization of rhodamine B increased the absorption of visible light and provided excited electrons.In addition,the suitable conduction band(CB)positions in the ternary hybrid can form a cascade structure,which effectively promotes the transfer and separation of photogenerated electrons and holes.