Study On Synthesis And Modified Photocatalytic Properties Of Ultra-thin And Super-large Bi₄Ti₃O₁₂ Nanosheets

large size Bi₄Ti₃O₁₂ nanosheets were prepared by hydrothermal method,and their photocatalytic properties were improved by modification.They were treated with Ag₂S,Au?Ag and NaBH₄ respectively.The samples were characterized by XRD,SEM,TEM,XPS,UV-vis DRS,BET,PL,FTIR,EIS and transient photocurrent response.With RhB as the target pollutant,the photocatalytic properties of the samples were systematically studied.The main research contents are as follows:?1?Bi₄Ti₃O₁₂2 nanosheets with highly exposed?010?surface were synthesized by hydrothermal method.SEM shows that the transverse size of Bi₄Ti₃O₁₂ nanosheets can reach 14 microns,and the average thickness of Bi₄Ti₃O₁₂ nanosheets is only 60nanometers,which means that the nanosheets have nearly 100%exposure?010?s urface.The photocatalytic activity of Bi₄Ti₃O₁₂2 nanosheets was analyzed by simulated solar irradiation degradation of RhB.The results showed that the photocatalytic activity of Bi₄Ti₃O₁₂ nanosheets was significantly enhanced compared with that of Bi₄Ti₃O₁₂nanoparticles with the size of 70 nm.The high photocatalytic activity of?010?surface can be attributed to the separation and migration of light-generated electrons and holes along[010]direction to?010?surface under the action of internal electric field.The calculated electronic structure shows that?010?surface energy is much larger than?100?and?101?surface.?2?Ag₂S-QDs were compounded on the surface of Bi₄Ti₃O₁₂ nanosheets by ion exchange method,and a new Ag₂S?QDs?/Bi₄Ti₃O₁₂ heterojunction composite photocatalyst was prepared.TEM results show that the two Ag₂S quantum dots with sizes of 40-70 nm and 7-17 nm are uniformly composite on the surface of Bi₄Ti₃O₁₂ nanosheets.The prepared Ag₂S/Bi₄Ti₃O₁₂ heterojunction composites have strong light absorption and efficient photogenerated electron-hole pair separation.Compared with Bi₄Ti₃O₁₂monomer,the photocatalytic activity of Ag₂S/Bi₄Ti₃O₁₂ heterojunction composite was significantly enhanced.The capture experiments of active species were carried out.The results showed that photogenic holes played the main roles in the photocatalytic process.Finally,a Z-type photocatalytic mechanism was proposed to explain the enhanced photocatalytic activity of Ag₂S/Bi₄Ti₃O₁₂ heterojunction composites.?3?Au and Ag nanoparticles of different sizes were compounded onto Bi₄Ti₃O₁₂nanosheets by light reduction to enhance the photocatalytic activity synergistically.Transmission electron microscopy?TEM?observation showed that larger size of Au particles?average size 20 nanometers?and smaller size of Ag particles?average size 8nanometers?were uniformly modified on the surface of Bi₄Ti₃O₁₂ nanosheets.Compared with Bi₄Ti₃O₁₂,the photocatalytic properties of Au-Ag@Bi₄Ti₃O₁₂ composites under ultraviolet,visible and simulated sunlight were significantly improved.Under ultraviolet irradiation,photocatalytic enhancement is mainly due to the effective separation of photogenerated electron-hole pairs caused by smaller size Ag particles;under visible irradiation,photocatalytic enhancement is mainly due to the LSPR effect of larger size Au particles;under simulated solar irradiation,the synergistic enhancement of photocatalytic activity of silver nanoparticles and gold nanoparticles.?4?Surface modification of Bi₄Ti₃O₁₂ nanoparticles was carried out by NaBH₄reduction method.Through experimental analysis,disordered surface layer related to oxygen vacancy defects was formed on the surface of Bi₄Ti₃O₁₂ nanosheets,and surface defect state was introduced into the forbidden band of Bi₄Ti₃O₁₂.The Bi₄Ti₃O₁₂ samples treated with NaBH₄ showed significantly enhanced visible light absorption.The experimental results show that the photocatalytic activity of Bi₄Ti₃O₁₂ samples treated with NaBH₄ under ultraviolet irradiation is significantly higher than that before treatment,because the surface defect state formed can be used as an electron acceptor,thus contributing to the separation of photogenerated electron hole pairs.In addition,the photocatalytic performance of Bi₄Ti₃O₁₂ samples treated with NaBH4 under visible light irradiation is also slightly improved,which is due to the fact that the surface defect state formed by NaBH₄ can be used as Visible absorption enhancement caused by surface defect state.