Two-dimensional Non-layered Metal Oxides And Chalcogenides:Electronic Structure Regulation And Their Applications In Photocatalysis

The greenhouse effect caused by the excessive use of fossil energy has seriously hindered the sustainable development of the community with a shared future for mankind.At the same time,it has also greatly prompted us to look for renewable and environmentally friendly clean energy as a substitute for fossil energy.Inspired by natural photosynthesis,researchers have found that under illumination,the semiconductor photocatalyst can gently carry out the conversion process of small molecules at room temperature and normal pressure,which was originally high-energy-consuming,such as formaldehyde(HCHO)photocatalytic oxidation and carbon dioxide(CO2)photocatalytic reduction,thus making the design and development of semiconductor catalysts are of great research significance.In this dissertation,through the design and development of various methods(doping,vacancy,heterojunction,etc.),we intend to regulate the electronic structure of two-dimensional non-layered semiconductors,and then hope to improve their photocatalytic activity.Moreover,through in-situ characterization methods and density functional theory calculations,we seek to explore the relationship between the microscopic electronic structure and the macroscopic photocatalytic performance,ultimately providing theoretical guidance for the development of high-performance semiconductor photocatalyst.The main contents of this dissertation are as follows:1.Defective Bi2WO6 ultrathin sheets realize high-rate HCHO photooxidation:photooxidation provides a promising strategy for removing the dominant indoor pollutant of HCHO,while the underlying photooxidation mechanism is still unclear,especially the exact role of H2O molecules.Herein,this work utilizes in-situ spectral techniques to unveil the H2O-mediated HCHO photooxidation mechanism.As an example,the synthetic defective Bi2WO6 ultrathin sheets realize high-rate HCHO photooxidation with the assistance of H2O at room temperature.In-situ electron paramagnetic resonance spectroscopy demonstrates the existence of ·OH radicals,possibly stemmed from H2O oxidation by the photoexcited holes.Synchrotron-radiation vacuum Uultraviolet photoionization mass spectroscopy and z218O isotope-labeling experiment directly evidence the formed ·OH radicals as the source of oxygen atoms,trigger HCHO photooxidation to produce CO2,while in-situ Fourier transform infrared spectroscopy discloses the HCOO*radical is the main photooxidation intermediate.Density-functional-theory calculations further reveal the ·OH formation process is the rate-limiting step,strongly verifying the critical role of H2O in promoting HCHO photooxidation.This work first clearly uncovers the H2O-mediated HCHO photooxidation mechanism,holding promise for high-efficiency indoor HCHO removal at ambient conditions.2.In-plane heterostructured Ag2S-In2S3 atomic layers enabling boosted CO2 photoreduction:sluggish separation and migration kinetics of the photogenerated carriers account for the low-efficiency of CO2 photoreduction into CH4.Design and construction two-dimensional(2D)in-plane heterostructures demonstrate to be an appealing approach to address above obstacles.Herein,this work fabricates 2D in-plane heterostructured Ag2S-In2S3 atomic layers via an ion-exchange strategy.Photoluminescence spectra,time-resolved photoluminescence spectra,and photoelectrochemical measurements firmly affirm the optimized carrier dynamics of the In2S3 atomic layers after the introduction of in-plane heterostructure.In-situ Fourier transform infrared spectroscopy spectra and DFT calculations disclose the in-plane heterostructure contributes to CO2 activation and modulates the adsorption strength of CO*intermediates to facilitate the formation of CHO*intermediates,which are further protonated to CH4.In consequence,the in-plane heterostructure achieves the CH4 evolution rate of 20 μmol g-1 h-1,about 16.7 times higher than that of the In2S3 atomic layers.In short,this work proves construction in-plane heterostructures as a promising method for obtaining high-efficienc y CO2-to-CH4 photoconversion properties.3.Photocatalytic CO2 reduction boosted by Metaln+-Metalδ+ pair sites:the major obstacle for selective CO2 photoreduction to C2 hydrocarbons lies in the difficulty of C-C coupling,which is usually restrained by the repulsive dipole-dipole interaction between adjacent carbonaceous intermediates.Herein,this work first constructs metal sulfide atomic layers featuring abundant Metaln+-Metalδ+pair sites(0<δ<n),aiming to tailor asymmetric charge distribution on the carbonaceous intermediates and hence trigger their C-C coupling for selectively yielding C2 hydrocarbons.As an example,this work first fabricates Co-doped NiS2 atomic layers possessing abundant Ni2+-Niδ+(0<δ<2)pairs,where Co doping strategy can ensure higher amount of Ni2+-Niδ+pair sites.In-situ Fourier-transform infrared spectroscopy,quasi in-situ Raman spectroscopy and density-functional-theory calculations disclose the Ni2+-Niδ+ pair sites endow the adjacent CO intermediates with distinct charge density,thus decreasing their dipole-dipole repulsion and hence lowering the rate-determining C-C coupling reaction barrier.As a result,in simulated flue gas(10%CO2 balance 90%N2),the ethylene selectivity for Co-doped NiS2 atomic layers reaches up to 74.3%with an activity of 70 μg g-1 h-1,outperforming previously reported photocatalysts under similar operating conditions.