Simulation Study On Adsorption Characteristics And Catalytic Potential Of Modified Zinc Oxide For VOCs

Volatile organic pollutants（VOCs）cause more and more serious pollution to the building environment.Among many treatment technologies,adsorption technology and catalytic technology are used to treat indoor volatile organic pollutants in buildings with their advantages of green and pollution-free.As a kind of material with adsorption and catalytic effects,semiconductor materials have been widely concerned and applied in the photoelectric and catalytic industries.Computational material science has become one of the key research methods in parallel with experiment and theory.When it is difficult to screen functional materials through experimental methods,molecular simulation calculation can be used to screen some substances with adsorption and catalytic effects.Simulation technology has become an important means of material research and development.In this paper,zinc oxide is selected as the research object functional material.Based on the density functional theory and molecular simulation method,the surface physical properties of zinc oxide are explored.Through the surface modification treatment,the material properties after modification are studied.The results show that the band gap energy of modified zinc oxide is reduced,and its electronic distribution is increased compared with that of pure zinc oxide,Therefore,the modified zinc oxide is more sensitive to surface substances within the energy band.Then,based on the GGA+U correction method,taking Ce atom doping as an example,the structural changes and binding energy results of Ce atom doped at three different doping sites on the surface of modified zinc oxide were analyzed,and the optimal doping sites were selected.The results showed that when Ce atom was doped at Zn-Ce sites,the change of bond length around the doping sites was similar to that of other two sites,and the binding energy reached 2.512e V,it is much larger than Ctr-Ce point（1.552e V）and O-Ce point（1.215e V）,so when Ce atom is doped at Zn-Ce point,the modified doping system has the highest compactness and the most stable structure.Formaldehyde is further selected as the adsorption object.Based on the geometric structure,adsorption distance,adsorption energy and charge density diagram,the pure modified zinc oxide surface,the modified zinc oxide surface doped with Ce atom,the modified zinc oxide surface doped with Y atom,the modified zinc oxide surface doped with Ce atom and Y atom,and the adsorption of formaldehyde molecules are discussed respectively.The results show that the O atom in formaldehyde is more easily adsorbed on the modified zinc oxide surface,The adsorption of formaldehyde on the surface of modified zinc oxide doped with Ce and Y atoms is enhanced,and there is a trend of bonding between the Ce atom and the O atom of formaldehyde on the surface of modified zinc oxide doped with Ce and Y atoms.At the same time,the interference of common water molecules in the air on adsorption was investigated.The results showed that there was competitive adsorption between water molecules and formaldehyde,and the adsorption of formaldehyde was promoted on the surface of modified zinc oxide doped with Y atoms.For pure modified zinc oxide,modified zinc oxide after Ce doping,modified zinc oxide after Y doping and modified zinc oxide system co-doped with Ce and Y,the photoelectric effect and catalytic potential of these four systems are analyzed respectively.The results show that the energy band value of modified zinc oxide is effectively reduced and the charge transfer efficiency of modified zinc oxide is improved by doping,effectively improve the ability of bound charge of modified zinc oxide and the degree of light response in the visible light range.The most remarkable thing is that the modified zinc oxide has three new light absorption peaks in the near-visible light region with the wavelength of 400nm to 550nm,which are about35346cm^-1,39263cm^-1 and 60202cm^-1,respectively,and the doped modified zinc oxide has stronger ability to generate·O₂^-,which can effectively improve the catalytic performance of modified zinc oxide.Finally,based on the analysis of catalytic reaction mechanism,it is found that the Ce and Y atoms doped on the surface of modified zinc oxide can provide sites for electron migration in the conduction band,prolong the separation time of holes and electrons,and allow sufficient time for holes and electrons to transfer to the surface of modified zinc oxide to react with external substances,further leading to more·O₂^-produced by e^-and oxygen on the surface of modified zinc oxide,the degradation intensity and rate of VOCs by modified zinc oxide doped with Ce and Y atoms are enhanced,and VOCs are finally converted into a series of non-toxic substances.