Morphology Control Preparation And Photocatalytic Performance Of ZnO And Its Composites

Energy and environmental issues are two major problems facing humanity in the world.In our country,more and more attention is now being paid to environmental protection,and the“elimination of poor type V water”action is also ongoing.However,wastewater containing organic pollutants is still a problem to be solved.In recent years,semiconductor photocatalysis has performed prominently in the treatment of water pollution.Semiconductor photocatalytic degradation of organic pollutants is an effective method for environmental pollution control,and it has been at the forefront of environmental governance research.It can quickly convert organic pollutants into CO₂,water and inorganic salts.Its advantages are high efficiency,low cost,low reaction temperature requirements,small energy requirements,and complete degradation of pollutants.Among the many semiconductors that can be used in photocatalysis,ZnO is one of the most promising materials.It has the advantages of simple production process,low cost,non-toxic and harmless,various shapes,good chemical and optical stability,and abundant resources.However,the ZnO photocatalyst is far from the large-scale application,and it is necessary to further increase the photocatalytic reaction activity and broaden the photoresponse range so that it has visible light catalytic activity.The hydrothermal reaction is the most commonly used methods to prepare ZnO materials.In this paper,the effect of different factors on the ZnO materials was studied,the ZnO materials with higher photocatalytic activity were sought,and the method of broadening the photoresponse range of ZnO was explored.ZnO materials and ZnO/Fe₂O₃ were prepared by hydrothermal/solvothermal reaction using zinc acetate（Zn（COOH）₂·2H₂O）and sodium hydroxide（NaOH）as raw materials and ethylene glycol（EG）as an auxiliary agent.1.The influence of the addition amount of precipitant NaOH on the preparation of ZnO by hydrothermal reaction method was studied.The molar ratio of Zn²⁺to OH^-was changed by the amount of NaOH added to the reaction materials.Different morphologies of ZnO materials were obtained.The molar ratios of Zn²⁺and OH^-were1:1,1:3,and 1:6,respectively.Under the conditions,rod-shaped ZnO,small-particle ZnO and sheet-like ZnO were prepared.ZnO materials with different morphologies can be prepared by changing the amount of precipitant added in the hydrothermal reaction.Through a series of characterizations,the correlation between the crystal structure and photocatalytic activity of ZnO materials were studied.Different morphologies of ZnO materials show different photocatalytic activities due to the difference in the polar surface exposure ratio.It was found that the sheet-like ZnO material has the highest polar surface exposure ratio and also has the highest photocatalytic activity.The morphology of ZnO has a significant effect on its photocatalytic activity.2.Solvothermal method was used to prepare ZnO with different morphology by adjusting ethylene glycol/water volume ratio in ethylene glycol/water solvent.The ZnO prepared at a higher ethylene glycol content has a spherical structure,and the ZnO prepared at higher water content tends to a sheet-like structure.The ZnO with different morphologies all have hexagonal wurtzite crystal structure,but their（002）/（100）diffraction peaks have different intensity.Spherical ZnO has a larger proportion of（002）crystal plane and the largest exposed polar surface area.Globular ZnO and cracked spherical ZnO with gully wrinkles on the surface have a smaller band gap and a wider light absorption range than sheet-like ZnO.At the wavelength of 365 nm,the efficiency to degrade of methyl orange by spherical ZnO and ruptured spherical ZnO is high,and the defects in the grooves formed on the surface of ZnO crystals generate crystal defects,and these defects promote the separation of photo-generated electron-hole pairs on ZnO,thereby enhancing the photocatalytic activity of ZnO.3.Hydrothermal reaction（solvent heat）was used to prepare different ZnO/Fe₂O₃composites by changing the hydrothermal reaction time and temperature.The increase of hydrothermal reaction temperature can increase the size of ZnO nanoparticles on the surface of ZnO/Fe₂O₃ composites,and even generate new morphologies of ZnO.At the same time,it causes the ZnO coating to become sparse.The prolongation of hydrothermal reaction time can also increase the size of ZnO nanoparticles on the surface of ZnO/Fe₂O₃ composites,but the ZnO coating layer is more close.Under visible light irradiation above 400 nm,ZnO/Fe₂O₃ composites exhibit visible light photocatalytic activity.The arrangement of ZnO coating on the surface of ZnO/Fe₂O₃composites plays an important role in the photocatalytic activity of ZnO/Fe₂O₃composites.The tightness of the coating can optimize the visible light catalytic activity of ZnO/Fe₂O₃ composites.Due to the presence of magnetism,ZnO/Fe₂O₃composites can be recovered and reused by an external magnetic field,which has a good industrial application prospect.