Preparation And Photocatalytic Mechanism Of ZnO Matrix Composites

ZnO is an n-type direct wide bandgap semiconductor material with a forbidden band width of 3.37eV.Due to its excellent photoelectric performance and chemical stability,ZnO is widely used in photocatalysis,air purification,antibacterial materials and other aspects.However,a single ZnO syetem can only respond to ultraviolet light with a wavelength less than 400nm,which greatly limits its effective utilization of solar energy.At the same time,the photogenerated electrons and holes can easily recombination,which leads to the decrease of quantum efficiency.These defects limit the catalytic performance of ZnO.Therefore,Cu₂O/ZnO composites,CNTs/ZnO composites andɑ-Fe₂O₃/ZnO composites were prepared in order to improve the photocatalytic performance of ZnO,and the effects of different conditions on the structures,morphologies and properties of the composites were studied in this paper.The research contents of this paper are summarized as follows:1.The Cu₂O/ZnO composites were successfully prepared by simple hydrothermal method and water bath chemical reduction method,and used CuSO₄·5H₂O as copper source and hydrazine hydrate（N₂H₄·H₂O）as reducing agent.The effects of Cu/ZnO molar ratios,reaction temperatures and reaction times on the structures,morphologies and properties of Cu₂O/ZnO composites were investigated.At the same time,the growth mechanism and photocatalytic degradation mechanism of Cu₂O/ZnO composites were briefly discussed.The results showed that when the reaction temperatures and reaction times were fixed,the degradation efficiency of MB in Cu₂O/ZnO composites increases first and then decreases with the increase of Cu/ZnO molar ratios.Cu₂O/ZnO（M3）with a Cu/ZnO molar ratio was10%has the best photocatalytic performance,and the degradation efficiency of visible light for 75min reached to 94.3%.And the forbidden band width of Cu₂O/ZnO is smaller than that of pure ZnO.The degradation efficiency of MB in a series of Cu₂O/ZnO samples increase first and decrease then,which were prepared by changing the reaction temperatures or reaction times when the Cu/ZnO molar ratio was 10%.The photocatalytic experiments showed that the best preparation conditions for the Cu₂O/ZnO were:Cu/ZnO molar ratio was10%,reaction temperature reached 70℃,reaction times maintained 60min.2.The CNTs/ZnO composites were prepared by hydrothermal method.The influences of the contents of CNTs on the crystal structures,morphologies and properties of CNTs/ZnO composites were researched.The growth mechanism and photocatalytic mechanism of CNTs/ZnO composites were also investigated.It was found that the addition of CNTs can enhance the specific surface area and visible light absorption intensity of ZnO,and reduce the recombination between photoelectron and holes under visible excitation.so that the photocatalytic performance of CNTs/ZnO composites was significantly improved compared with pure ZnO under visible light.The sample has the best catalytic performance when the content of CNTs was 20mg,the degradation efficiency under visible light for 75min reached to 91.5%.3.A series ofɑ-Fe₂O₃/ZnO composites were prepared by simple hydrothermal method with Fe（NO₃）·9H₂O as the iron source.The effects of different reactions on the structures,morphologies and properties ofɑ-Fe₂O₃/ZnO composites were researched by changing Fe/Zn molar ratios and recation pH.The growth mechanism and photocatalytic degradation mechanism ofɑ-Fe₂O₃/ZnO composites were also investigated.The results showed that the photodegradation efficiency ofɑ-Fe₂O₃/ZnO composites first increases and then decreases with the increase of Fe/Zn molar ratios when the reaction pH was 11.Theɑ-Fe₂O₃/ZnO with a Fe/Zn molar ratio was 1:4 has the strongest photocatalytic activity,and the degradation efficiency under visible light for 75min reached to 93.6%.When the Fe/Zn molar ratio was1:4,the photocatalytic activity of the sample first increases and then decreases with the increase of reaction pH.