Study On Piezocatalytic Performance And Mechanism Of Bismuth Vanadate Materials For The Removal Of Contaminants In Water

Piezocatalysis induced by the polarization of piezoelectric materials can convert low-cost and environmentally-friendly mechanical energy,such as sound,water waves,vibration and so on,into chemical energy,and remove refractory micro-pollutants in water,which has attracted widespread attention.The current research on piezocatalysis in environmental pollution control is still in its infancy.There are urgent problems to be sovled,such as few types of piezocatalysts,low treatment efficiency,single pollution control function,and unclear reaction mechanism.In this study,two new metal-loaded bismuth vanadate pieocatalysts are developed to address the shortcomings of piezocatalysis,and the performance and mechanism of piezocatalysts for removing contaminants in water are studied.This study provides theoretical support and technical reference for the development and environmental application of high efficiency piezocatalytic materials.The main contents of this study are as follows:（1）Fe-loaded bismuth vanadate catalyst（Fe/Bi VO₄）is prepared by an impregnation method,in which Fe is uniformly distributed on the monoclinic Bi VO₄ surface in a mixed valence state of divalent and trivalent.The as-synthesized Fe/Bi VO₄ has obvious piezoelectric response according to piezo-response force microscopy test.It performs superior piezocatalytic performance for hydrogen peroxide production and organic contaminants degradation,with 86%of 4-chlorophenol（4-CP）removal and 68μmol/L hydrogen peroxide accumulation in 120 min.The presence of Fe can significantly improve the utilization efficiency of hydrogen peroxide in the reaction system.Therefore,this study can achieve the piezo-Fenton-like reaction for the degradation of organic contaminants in water.（2）Au nanoparticles modified bismuth vanadate（Au/Bi VO₄）is successfully prepared via a deposition-precipitation method in a hot urea solution.Au nanoparticles are uniformly distributed on the surface of the monoclinic Bi VO₄ in a zero-valent metal state,and the particle size is 5-15nm.The synthesized Au/Bi VO₄ performs stronger piezoelectric response than Fe/Bi VO₄ according to piezo-response force microscopy result.It also exhibits better piezocatalytic performance than Fe/Bi VO₄.As a bifunction catalyst,Au/Bi VO₄ performs synergistic effect on the simultaneous removal of 4-CP and Cr（VI）in water under ultrasonic vibration,achieving 91%of4-CP degradation and 83%of Cr（VI）reduction in 120 min.The piezocatalytic performance of Au/Bi VO₄ can be attributed to the internal electric field formed by ultrasonic vibration to promote the separation of free electron-hole pairs.Using tert-butanol（TBA）as the hydroxyl radical probe,the hydroxyl radical was determined to be the active species for 4-CP degradation through the calculation of reaction kinetics.According to the measurement of hydrogen peroxide accumulation and the reaction of hydrogen peroxide with 4-CP or Cr（VI）,it is determined that hydrogen peroxide is generated from dissolved oxygen through a multi-electron reduction pathway.And Cr（VI）is reduced mainly by a rapid chemical reaction with hydrogen peroxide.