| With the rapid development of urbanization,the pollution problem of the environment in which people live is also becoming more and more serious.As a necessary environmental factor for human survival,atmospheric environmental pollution seriously affects people’s physical health,and formaldehyde（HCHO）is one of the most common indoor air pollutants,poses a serious threat to human health due to its volatility,high toxicity,and widespread existence.Seeking a method for efficiently degrading formaldehyde has become an urgent problem to be solved.Photocatalysis is increasingly favored by researchers because of its advantages of low energy consumption,low cost,high degradation efficiency,and no secondary pollution.As the core of photocatalytic technology,most photocatalytic materials have the disadvantages of low solar energy utilization efficiency and rapid recombination of electron-hole pairs.Many recent related studies have reported that the piezoelectric effect in the piezoelectric catalyst can be combined with photocatalytic technology to improve the efficiency of catalyst degradation of pollutants,therefore,the efficient degradation of organic pollutants by catalysts can be achieved by using piezoelectric photocatalytic coupling methods.In the case of two-dimensional semiconductor piezoelectric photocatalytic materials,the mechanism of piezoelectric photocatalytic coupling,the formation pathway of reactive oxygen species（ROSs）,and the mechanism of degrading organic pollutants in the atmosphere are not well understood.This thesis will take the two-dimensional（2D）semiconductor piezoelectric material Mo S2 as the piezoelectric catalyst model,CASTEP and DMol3 module were carried out to study the piezoelectric photocatalytic performance of monolayer 2H-Mo S2,which is divided into two Part for discussion:（1）The traditional MoS2 light utilization rate is poor,and the effective separation rate of the photogenerated electron-hole pairs is low,and its photocatalytic performance is suppressed.In this work,the layer 2H-Mo S2 structure was used as a piezoelectric photocatalyst to improve the photocatalytic performance of 2H-Mo S2 by applying the piezoelectric effect generated by stress.To explore piezo-photocatalytic synergies of 2H-Mo S2,four aspects could be considered in detail:i)piezoelectricity of 2H-Mo S2;ii)photocatalysis of 2H-Mo S2;iii)generation of×OH and×O2-radicals;iv)pathways of piezoelectric-photocatalytic synergy to degrade HCHO.The results show that strain can greatly control and improve the band gap and light absorption spectra of 2H-Mo S2,indicating that the piezoelectric effect plays an important role in regulating the photocatalysis of 2H-Mo S2.At the same time,the piezoelectric effect forms a built-in electric field within the material can promote the generation of free radicals on 2H-Mo S2,and it can be determined that the free radicals are stable on the surface of 2H-Mo S2 for pollutant degradation.The piezoelectric effect not only improves the utilization rate of hydroxyl radical for degradation HCHO and releases more energy.In summary,the piezoelectric effect is generated by applying strain,which forms a built-in electric field,promotes the effective transfer of the photocarrier,inhibits the recombination of photogenerated electron pairs,and thus realizes the efficient degradation of HCHO through piezoelectric-photocatalytic synergy.（2）Considering that the piezoelectric effect has limited ability to regulate the photocatalytic properties of 2H-Mo S2 materials,we use the 2H-Mo S2 and graphene material composite method to modify the materials.In this section,we study the piezoelectric properties,photocatalytic properties and adsorption energy of formaldehyde molecules under strains.The results show that compared with the single-layer 2H-Mo S2 system,the 2H-Mo S2/graphene composite system improves the absorption capacity of visible light,induces more electron hole pairs to be generated,and improves the photocatalytic efficiency of the system.In addition,the adsorption of surface molecules by 2H-Mo S2/graphene composite system is stronger,and the piezoelectric effect can well regulate the adsorption performance of surface molecules.The efficiency of photocatalytic degradation of VOCs is improved,indicating the feasibility of piezoelectric photocatalytic degradation of VOCs in 2H-MoS2/graphene composite systems. |
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