The Study Of Structure Regulation And Property For Bi Based Photocatalysts

With the rapid development of global industry,energy shortage and environmental pollution have been regarded as the two major challenges facing mankind.Semiconductor photocatalysis technology has attracted the attention of scientists all over the world in the fields of clean hydrogen energy synthesis,chromium（Ⅵ）reduction in industrial wastewater and atmospheric pollutant NO_x removal because of its advantages of fast reaction speed,low energy consumption and environmental friendliness.Although bismuth（Bi）based semiconductor photocatalysts have been widely used,the low separation efficiency of photoelectron-hole（e^--h⁺）pairs still results in the unsatisfactory photocatalytic performance.Based on this,the separation efficiency of photogenerated e^--h⁺pairs in Bi based semiconductor photocatalysts was improved by constructing new heterojunction,noble metal Ag loading,sulfur vacancy and oxygen vacancy（OVs）.The main research contents are as follows:（1）Construction of three-dimensional/three-dimensional（3D/3D）Bi₂S₃/Cd S heterojunctions and photocatalytic reduction properties for Cr（Ⅵ）.Bi₂S₃/Cd S heterojunction was constructed by hydrothermal method.The performance of 0.5-Bi₂S₃/Cd S photoreduction Cr（Ⅵ）prepared with 0.5 mmol of Bi₂S₃ was the best,and the efficiency of Cr（Ⅵ）reduction was close to 100%when the light was exposed for6 min.The results of electron spin resonance and free radical scavenging experiments show that e^-and·O₂^-are the main active substances in reducing Cr（Ⅵ）.The work functions of Bi₂S₃ and Cd S were obtained by ultraviolet photoelectron spectroscopy（UPS）and density functional theory（DFT）,respectively.The photocatalytic carrier migration path and the possible photocatalytic reaction mechanism in heterojunction were discussed.This work provides a new idea for the construction of a new heterojunction and the study of photocatalytic efficient reduction of Cr（Ⅵ）.（2）Construction of three-dimensional/two-dimensional（3D/2D）Bi₂S₃/Bi₅O₇Br heterojunction and the study of hydrogen and oxygen production by water splitting.2D Bi₅O₇Br+OVs（Bi₅O₇Br+oxygen vacancy）nanosheets were prepared on the surface of3D Bi₂S₃ nanorods by hydrothermal method,and 3D/2D Bi₂S₃/Bi₅O₇Br heterojunction was constructed by ion exchange at the interface.The addition amount of Bi₂S₃ has significant effects on the 3D/2D Bi₂S₃/Bi₅O₇Br heterojunction on the morphology,microstructure and photoelectrochemical properties.The 0.3-Bi₂S₃/Bi₅O₇Br photocatalyst was prepared when the amount of Bi₂S₃ was 0.3 mmol.The hydrogen evolution rate of 38mmol·g^-1·h^-1 is 13,38,9.5 and 1.9 times that of Bi₂S₃,Bi₅O₇Br,0.6-Bi₂S₃/Bi₅O₇Br and 0.2-Bi₂S₃/Bi₅O₇Br,respectively.The oxygen production rate of 0.3-Bi₂S₃/Bi₅O₇Br was 1043mmol·g^-1·h^-1,which was 2.7,3.0,1.9 and 1.4 times that of Bi₂S₃,Bi₅O₇Br,0.6-Bi₂S₃/Bi₅O₇Br and 0.2-Bi₂S₃/Bi₅O₇Br respectively.After six photocatalytic cycles,the photocatalytic hydrogen evolution and oxygen generation capacity of 0.3-Bi₂S₃/Bi₅O₇Br did not decrease significantly,indicating that the catalyst has good stability.Finally,the possible mechanism of photocatalytic hydrogen evolution and oxygen generation in 3D/2D Bi₂S₃/Bi₅O₇Br heterojunction is discussed.（3）Synthesis of oxygen-vacancy-rich Ag/Bi₅O₇Br nanosheets and their photocatalytic properties for oxygen production and NO removal.We report on one-step synthesis of Ag/Bi₅O₇Br nanosheets with rich oxygen vacancies by a facile liquid phase reduction method.Under visible light irradiation on oxygen-vacancy-rich Ag/Bi₅O₇Br for 50 min the photocatalytic NO removal ratio is up to 64.65%,which is about 1.6 times that of pure Bi₅O₇Br nanosheets.The average oxygen generation rate of oxygen-vacancy-rich Ag/Bi₅O₇Br is 823mmol·g^-1·h^-1,which is nearly 10 times higher than that of Bi₅O₇Br.DFT calculation showed that OVs incorporation and plasmonic Ag synergistic enhanced the adsorption of NO by Bi₅O₇Br,and improved the separation efficiency of photogenerated e^--h⁺pairs in Bi₅O₇Br.This work highlights the great potential of defects and plasmonic metals on synergistic enhancement in photocatalytic NO removal and oxygen evolution.