Photocatalytic Properties And Mechanism Of ZnO Composites

At present,the treatment of organic pollutants in water by semiconductor photocatalysis technology has aroused extensive research interests.This method can converts solar energy into chemical energy,and then decompose organic pollutants in water.It has also the characteristics of low production cost and no secondary pollution.Among many semiconductor photocatalysts,ZnO has attracted wide attention in the field of photocatalysis due to its non-toxic,simple preparation and good chemical stability.ZnO has a wide band gap(3.3 e V)and large binding energy(60 me V),which leads to the easy combination of photogenerated electrons and holes.Although ZnO has good photocatalytic activity under ultraviolet(UV)light,but it can hardly be excited in the visible light range,so it has very low utilization rate for sunlight.ZnO can be modified by many methods to improve its light absorption capacity under visible light,thereby increasing the commercial application value of ZnO.In this paper,the photocatalytic properties of ZnO were studied by the nonmetal doping and semiconductor composite.N-doped ZnO and MoS₂/ZnO photocatalysts were prepared by sol-gel and hydrothermal method respectively,and their morphologies,optical properties and photocatalytic properties were studied by a series of characterization methods.The main contents of the study are as follows:1.N-doped ZnO photocatalyst was prepared by sol-gel method.SEM shows that the morphology is irregular nanorods,and the band gap is 2.25 e V,which is smaller than that(3.3 e V)of traditional ZnO.XPS analysis shows that the doping of N atomic is conducive to increase the concentration of O vacancy on the surface of ZnO,and can improve its photocatalytic performance by increasing the active sites on the surface of photocatalyst.The result of photocatalytic experiments shows that N-doped ZnO photocatalyst has better photocatalytic activity than pure ZnO.That is,under the action of N-doped ZnO photocatalyst,methylene blue(MB)can be completely degraded within 60 minutes in the UV light,and the degradation rate also can reach 80%under visible light for 180 minutes.According to the first-principles calculation,the results shown that the doping of N can reduce the band gap of ZnO due to N element can insert an intermediate energy level in the energy band of ZnO,reducing the required energy for the transition of electrons from the conduction band to the valence band,and making the transition easier.Moreover,this is also conducive to the separation of photogenerated electrons and holes of ZnO,so as to improve the photocatalytic activity of ZnO.2.MoS₂/ZnO composite photocatalysts with different MoS₂contents were prepared by hydrothermal method with zinc acetate(Zn(CH₃COO)₂·2H₂O),sodium hydroxide(Na OH),sodium citrate(Na₃C₆H₅O₇·2H₂O),ammonium molybdate tetrahydrate((NH₄)₆Mo₂₄.4H₂O)and thiourea(CH₄N₂S)as raw materials.XRD results show that ZnO with MoS₂has better crystallinity.The UV-vis results show that the optical absorption range of MoS₂/ZnO composite is moved to the visible region and the band gap is reduced compared to that of pure ZnO.Through XPS analysis,we can know that O vacancy content on the surface of MoS₂/ZnO photocatalyst is higher than that of pure ZnO,which can promote the photocatalytic activity of the sample.Photocatalytic experiments show that when the mass ratio of MoS₂to ZnO is 3%,the degradation rate of MB is the highest in visible light,that is,the degradation rate reaches 88%within180 minutes,and the degradation efficiency is 2.4 times than that of pure ZnO.