Study On Synthesis Of Novel Niobate And Tantalate Based Photocatalysts With Low Dimensional Heterojunction Structure And Visible Light Driven Photocatalytic Performance And Mechanism

Semiconductor photocatalytic technology is a promising techonology because of its advantages of high efficiency and greenness in environmental purification and clean energy synthesis.With excellent ferroelectric,piezoelectric and photoelectric property,niobate and tantalates has good heterogeneous catalytic activities and chemical stability,which has been the research focus in multi-functional environmental materials field.However,niobate and tantalite-based photocatalysts fabricated by conventional synthesis have the disadvantages with low photoresponse range,high photo-generated carrier recombination rate and low light utilization rate,which limit their applications.Therefore,this study focused on niobate and tantalate-based photocatalysts synthesized by low temperature wet chemical strategy,and fabricated serial novel low-dimensional semiconductor heterojunction photocatalysts based on 0D/2D,2D/2D and 2D/1D strategy.The morphology,mechanism of interfacial charge transfer and visible light responsive catalytic performance of these low-dimensional semiconductor heterojunction photocatalysts were studied.The main research contents and conclusions are listed as follows:（1）Bi nanodots decorated Bi₃Nb O₇ nanosheets as an 0D/2D heterostructured composite was synthesized by a two-step wet chemical method.Both XPS analysis and density functional theory（DFT）calculations confirm that a strong covalent interaction between Bi atom of Bi nanodots and Bi-O layer on the surface of Bi₃Nb O₇ nanosheets.Moreover,ESR analysis and trapping experiments confirmed the activation of molecular oxygen into superoxide radicals（·O₂^-）and singlet oxygen（¹O₂）by the composite under visible light illumination for degradation of ciprofloxacin（CIP）.The photocatalytic degradation rate of CIP by the Bi/Bi₃Nb O₇composites is about 4.6 times higher than that by the pristine Bi₃Nb O₇.The Bi/Bi₃Nb O₇ photocatalyst still revealed high photocatalytic activity and structure stability even after five cycles.（2）Novel 2D/2D nanojunction architectures of Ba₅Nb₄O₁₅/g-C₃N₄photocatalysts with powerful interfacial charge transfer are rationally designed by solvothermal method coupled sintering process.Advanced electron microscopy analysis elucidates the layered hexagonal nanosheets were coupled on the surface of ultrathin g-C₃N₄ forming a 2D/2D nanojunction.More importantly,XPS experiments and theoretical calculations together illustrate that a strong interfacial charge transfer existed between the g-C₃N₄ layer and Ba-O layer of the Ba₅Nb₄O₁₅nanosheets,which could accelerate the interfacial charge separation efficiency.Ba₅Nb₄O₁₅/g-C₃N₄（1:20）sample displayed a remarkable photocatalytic H₂evolution rate in oxalic acid solution,nearly 2.35 times higher than that of single g-C₃N₄ under visible light and exhibits an outstanding photostability even after four cycles.This research also explores the photocatalytic hydrogen production performance of composites under several sacrificial agent,which gives a probe into the possibility of practical application.（3）This research composited visible-light-responsive Bi₃Ta O₇ quantum dots/ultrathin g-C₃N₄ 0D/2D via facile solvothermal method coupled ultrasonic strategy.It can be observed in that Bi₃Ta O₇ quantum dots were well dispersed on the surfaces of nanosheets with uniform lateral sizes,whose average lateral size is about5 nm.Furthermore,the strong interaction between Bi₃Ta O₇ quantum dots and ultrathin g-C₃N₄disturbed the CN heterocycles by forming C=O bonds between C atoms of the N-（C）₃ group and O atoms of the Ta-O bond through the XPS analysis.The optimum composite displayed the superior photocatalytic activity for degradation of ciprofloxacin（CIP）,which were 4 and 12.2 times higher than those of bare Bi₃Ta O₇ and g-C₃N₄.The CPX degradation rate of the optimal composite is higher than those of pure Bi₃Ta O₇ and g-C₃N₄ and exhibits an outstanding photostability even after four cycles.Moreover,heterojunction photocatalysts has a preferable photocatalytic degradation performance for cephalosporin,which further explores its application in degrading broad-spectrum antibiotics.The enhanced photocatalytic activity of as-synthesized photocatalysts could be attributed to the synergistic effect of efficient Z-scheme charge separation,highly dispersed 0D Bi₃Ta O₇ nanocrystals,coordinating sites of 2D g-C₃N₄ NSs and the strong coupling between them.（4）A highly efficient,stable and visible light responsive 2D/1D Ba₅Ta₄O₁₅/Ag VO₃ heterojunction photocatalysts was synthesized by a two-step,hydrothermal method strategy.The phase composition,morphology,optical properties and photogenerated charge behavior of Ba₅Ta₄O₁₅/Ag VO₃ composite were investigated by various characterization techniques.The as-obtained photocatalysts exhibited enhanced photocatalytic activities for azo dyes and antibiotics degradation,which are almost higher than that of printine Ag VO₃ and Ba₅Ta₄O₁₅.From the results of TEM、XPS and UV-vis DRS analysis,the generated trace amounts of Ag⁰ during preparation process mainly implied the photosensitivity of Ag VO₃.The photoelectrochemical experiments and theoretical calculations altogether indicate that the enhanced photocatalytic performance could be attributed to the synergy effect of the hole dominated charge transform path and localized surface plasmon resonance（LSPR）,further enlarging the cycled application and stability of single phase photocatalyst.In summary,this work provides theoretical and practical reference for the design,synthesis and photocatalytic mechanism of visible light responsive low-dimensional heterojunction photocatalysts.