Surface And Interface Regulation Of Bismuth Tungstate-based Materials For Enhanced Photocatalytic Activity

The rise of modern textile,pharmaceutical and other industries discharges a large amount of sewage,which has brought a serious threat to human life.Contaminated water seeps into the ground,further resulting in different degrees of soil and groundwater pollution.Therefore,the development of new technologies to repair the water environment is a prerequisite to ensure the sustainable development of mankind.The photocatalytic degradation technology has been favored by researchers due to its advantages of low cost and environmental protection.The key is the construction of high-efficiency photocatalyst.It has been found that bismuth tungstate（Bi₂WO₆）is a promising photocatalyst and has been widely used in the field of environmental remediation.However,bismuth tungstate still has the disadvantages of few surface active sites,low utilization rate of visible light,and rapid recombination of photo-generated charges,which makes its actual situation still limited.In this paper,the photocatalytic degradation ability of bismuth tungstate material was effectively improved by surface hydroxyl coordinated with oxygen vacancies,noble metal coupling,and heterostructure building and metal doping double modification.The main research contents of this paper are as follows:1.A series of Bi₂WO₆photocatalyst with surface rich in hydroxyl and oxygen vacancies were synthesized by adjusting the ratio of ethylene glycol（EG）to water in the hydrothermal synthesis process.The introduction of oxygen vacancies can effectively improve the separation efficiency of photogenerated charge and promote the conversion of molecular oxygen to superoxide radical（^·O₂^-）,thus improving the degradation performance of rhodamine B（Rh B）and tetracycline（TC）by photocatalyst.In addition,the hydroxyl group on the surface of Bi₂WO₆promotes the adsorption of hydroxyl-rich organic pollutant TC and further improves its degradation performance.The intermediate products during photocatalytic degradation were identified by mass spectrometry（MS）and the possible pollutant degradation pathways were speculated.The active species in the photocatalytic degradation process were investigated by combining electron spin resonance spectroscopy（ESR）and free radical trapping experiment,and the possible photocatalytic degradation mechanism was speculated.2.The Bi₂WO₆ultra-thin nanosheet composite modified by Ag nanoparticles was prepared by in-situ chemical reduction.The Ag/Bi₂WO₆-2 material with the optimized activity has remarkable photocatalytic degradation performance for Rh B and 2-mercaptobenzothiazole（MBT）,which is 1.93 and 1.53 times that of the Bi₂WO₆ultra-thin nanosheet,respectively.The experimental results show that the close interface structure between the Ag nanoparticles and Bi₂WO₆enhances the separation efficiency of photogenerated carriers and promotes the conversion of molecular oxygen to^·O₂^-.The ESR and free radical capture experiments showed that^·O₂^-and hole（h⁺）played important roles in the photocatalytic degradation of organic pollutants.In addition,the possible paths for the photocatalytic degradation of Rh B and MBT by Ag/Bi₂WO₆-2 were also explored by MS.3.Tin-doped bismuth oxychloride-supported bismuth tungstate composites（Sn-Bi OCl/Bi₂WO₆）were fabricated by tin chloride etching.the effects of heterostructure building and metal doping on the photogenerated charge separation efficiency were investigated systematically.The experimental results show that the Sn²⁺/Sn⁴⁺redox couple and the heterojunction interface promote the photo-generated charge separation and^·O₂^-generation.Compared with Bi₂WO₆and Bi OCl/Bi₂WO₆,the photocatalytic degradation rate of Rh B by the most active Sn-Bi OCl/Bi₂WO₆increased by 2.75 and 1.95 times,respectively.At the same time,bicarbonate and sulfite can activate hydrogen peroxide in the reaction system to further promote the generation of reactive oxygen species and accelerate the photocatalytic degradation of ciprofloxacin（CIP）.In addition,the possible photocatalytic degradation pathways of Rh B and CIP for Sn-Bi OCl/Bi₂WO₆were further explored by MS.The possible mechanism of photocatalytic degradation was deduced from ESR and free radical trapping experiments.