Study On Synthesis And Performance Of ZnO Based Phtotocatalysts With Coupled Semiconductors

In the past decades,a large number of available water resources have been polluted by industrial waste water.Tens of millions of people lack of available water resources,and human health is threatened by the caused water pollution.Semiconductor photocatalytic technology has the advantages of high degradation efficiency and no secondary pollution resulting in wide application prospect in the field of maintaining ecological environment.Among various semiconductors,ZnO nanomaterials have received extensive research due to their similar photocatalytic mechanism and band gap with TiO₂.However,ZnO photocatalyst still remains the following problems:First,ZnO with a wide band gap?3.37eV?can only absorb ultraviolet light from sunlight,which limits its application in practical sewage treatment.Second,the photoinduced electron hole pairs generated by the absorption of photon energy are easy to recombine,which greatly reduces the photocatalytic efficiency.Third,the use of ZnO as photocatalyst is not easy to be separated from the waste water,resulting in secondary pollution.To solve the above problems,different ZnO matrix composites were prepared by hydrothermal method and sol-gel method to improve its photocatalytic activity.The main research results are as follows:?1?ZnO/ZnS sheet-like photocatalyst was prepared by hydrothermal method,which was used to decompose methyl orange under ultraviolet light and sunlight.In this part,the effects of different sulfur time on ZnO/ZnS and different pH on ZnO degradaing methyl orange under ultraviolet irradiation were studied,respectively.The results showed that the photocatalytic efficiency of ZnO/ZnS with 6 h sulfuring time reached the highest degradation under ultraviolet light and sunlight?73.6%and 66.7%,respectively?.With the increase of the pH of the solution,the degradation rate of methyl orange increased under ultraviolet irradiation,reaching the highest 66.7%at the pH of 12.?2?Fe-ZnO/ZnS nanomaterials were prepared by sol-gel method.The experimental results show that Fe²⁺is doped in ZnO lattice,and the Fe-ZnO/ZnS nanomaterials possess strong absorption characteristics in the visible region.The order of degradation rate of methylene blue was Fe-ZnO/ZnS>Fe-ZnO>ZnO.The degradation rate of methylene blue by Fe-ZnO/ZnS was 85.7%.In addition,the photocatalytic mechanism of Fe-ZnO/ZnS nanomaterials was discussed.The enhancement of their photocatalytic activity was attributed to the doped Fe²⁺ions and the heterostructure formed between ZnS and ZnO.?3?Fe₃O₄/ZnO/ZnS composite photocatalyst was synthesized from zinc nitrate,iron nitrate and citric acid.The results showed that the photocatalytic activity of10%-Fe₃O₄/ZnO/ZnS composite photocatalyst was the highest under solar irradiation compared to other photocatalysts,and the degradation rates of methyl orange and methylene blue were 79.5%and 75.3%respectively under sunlight irradiation.The degradation rate of methyl orange and methylene blue was still above 65%after 3 cycles.The improvement of photocatalytic performance of Fe₃O₄/ZnO/ZnS is attributed to Fe³⁺ions entering ZnO lattice during the reaction and the heterostructure formed by ZnO and ZnS.However,the increasing content of Fe will decrease the photocatalytic performance of Fe₃O₄/ZnO/ZnS.