Construction,Properties And Mechanism Analysis Of Low-Dimensional Transition Metal Compounds Photocatalytic System

Photocatalytic technology has been extensively investigated as one of the significant approaches to solve the energy crisis and environmental purification.Therefore,the development of the stable,low-cost and efficient photocatalyst is an ambitious objective of ongoing research efforts.In recent years,low-dimensional transition metal compound semiconductor materials are great of interest owing to their superior photocatalytic activity.Moreover,their d-orbital energy levels are mostly in a semi-full state,this enables low-dimensional transition metal compound semiconductor materials to achieve the ideal balance between reactants and intermediates in the catalyst surface.However,most transition metal compound catalysts have the disadvantages of a narrowed photo-absorption,high probability of photogenerated carrier recombination,which hinders their further practical applications in the field of photocatalysis.In this thesis,low-dimensional transition metal oxides?Bi3TaO7?and sulfides?CdS,CuInS2/ZnS?are selected as photocatalyst.A series of composite photocatalysts were constructed through size control,loading of noble metal,construction of the heterojunction and coupling with biocatalyst.The photocatalytic performance of these composite photocatalysts was investigated by the photocatalytic degradation of antibiotics and hydrogen production under visible light irradiation.The objective was to investigate the charge separation and reaction mechanisms in these photocatalytic processes.The main research contents were listed as follows:1.Construction of low-dimensional Bi₃TaO₇-based heterojunction photocatalysts and their photocatalytic performance for the degradation of antibiotic?1?Preparation of Bi₃TaO₇ nanoparticles by hydrothermal method and its photocatalytic degradation activity for tetracycline hydrochloride?TC?Bi3TaO7 nanoparticle photocatalyst was prepared by the hydrothermal method for the first time.The as-prepared Bi3TaO7 nanoparticle size was 30-40 nm.Compared with bulk Bi3TaO7 prepared by high-temperature solid-state reaction,hydrothermal method could effectively reduce the size of Bi3TaO7.The photocatalytic TC degradation rate of Bi3TaO7 nanoparticles was twice than that of bulk Bi3TaO7 under visible light irradiation.The enhanced photocatalytic performance could be ascribed to the presence of surface defects in Bi3TaO7 nanoparticles,which promoted the separation of photogenerated electron-hole pairs.In addition,the influencing factors on the degradation of tetracycline hydrochlorides,such as catalyst content,initial concentration of degradation products and solution pH were also investigated.?2?Fabrication of Ag/Bi₃TaO₇ plasmonic photocatalyst with enhanced photocatalytic activity for degradation of tetracyclineA novel Ag/Bi3TaO7 plasmonic photocatalytic system was successfully fabricated by photoreduction of Ag on Bi3TaO7 nanoparticles.It is found that the plasmon resonance absorption of Ag not only expanded the light absorption range but also enhanced the charge transfer.As a result,the as-prepared Ag/Bi3TaO7 plasmonic photocatalytic system exhibited an enhanced photocatalytic degradation rate of TC.The optimal degradation rate was 85.4%when the content of Ag was 1 wt%,which was 1.5-fold higher than that of the bare Bi3TaO7.Finally,the photocatalytic mechanism for degradation of tetracycline by the Ag/Bi3TaO7 photocatalytic system was proposed.?3?Highly efficient visible-light-driven photocatalytic degradation of tetracycline by a direct Z-scheme g-C₃N₄/Bi₃TaO₇ nanocomposite photocatalystA g-C3N4/Bi3TaO7 direct Z-scheme heterojunction photocatalytic system was constructed by an in-situ solid-phase reaction.Studies have shown that the formation of heterojunction between g-C3N4 and Bi3TaO7 significantly improved the electron-hole separation,which was evidenced by transient photocurrent response and electrochemical impedance spectroscopy.The prepared g-C3N4/Bi3TaO7nanocomposite photocatalyst showed enhanced photocatalytic activity for the degradation of TC under visible light illumination.The optimal performance was achieved when the content of g-C3N4 was 50 wt%?the degradation rate arrived at 89.1%?which was 3.3 and 1.8 times that of the pristine g-C3N4 and Bi3TaO7 photocatalyst,respectively.The direct Z-scheme photocatalytic mechanism of the g-C3N4/Bi3TaO7composite photocatalytic system was proposed based on free radical capture experiments and EPR experimental results.2.Construction of low-dimensional transition metal sulfide-biohybrid system and its photocatalytic performance for hydrogen production under visible light?4?Construction of CdS/SW whole-cell biohybrid system for hydrogen productionA CdS/SW whole-cell biohybrid system was constructed by using CdS nanoparticles and the Gram-negative bacterium-Shewanella oneidensis MR-1?abbreviated as SW?.SW can express the hydrogenase that serve as a catalytic active site for hydrogen production after accepting photogenerated electrons from extracellular CdS and achieved enhanced hydrogen production.Under visible light illumination,the CdS/SW whole-cell biohybrid system showed the hydrogen production of 275.01?mol,which was 3.46 times higher than that of pure CdS nanoparticles?61.72?mol?.The electron transport chain knockout experiments of SW showed that photogenerated electrons on CdS were mainly transferred to intracellular hydrogenase through the redox electron transport protein and to reduce protons at the active site of hydrogenase.?5?Construction of CIZS QDs/SW intracellular whole-cell biohybrid system for hydrogen productionA unique intracellular photosensitized whole-cell photocatalytic system was constructed using CuInS2/ZnS quantum dots?CIZS QDs?and Shewanella oneidensis MR-1?SW?that expressing hydrogenases.CIZS QDs could be translocated into SW bacterial cells by a precise regulating,therefore achieving the effective electron transfer and avoiding the use of electron mediators.The fabricated CIZS QDs/SW intracellular photosensitized photocatalytic system exhibited the hydrogen production of 491.8?mol,which was 6.5 times higher than that of pristine CIZS QDs.The effective light absorption of CIZS QDs,fast interfacial electron transfer and high catalytic efficiency of hydrogenases were responsible for the enhanced hydrogen production of CIZS QDs/SW intracellular photosensitized photocatalytic system.Genetic engineering knockout experiments revealed that hydrogenase,as an active site for hydrogen production,played an important role in hydrogen production.Finally,a possible mechanism of the intracellular transmission process was proposed for CIZS QDs/SW intracellular photosensitized photocatalytic system based on the redox transfer protein knockout experiments and reported literature.