Preparation And Photocatalytic Activity Of Nano-ZnO,BiOX(X=Cl,Br,I) And Their Composites

In recent years,photocatalytic technology has broad application prospects in solving environmental pollution problems and energy conversion due to its low price,environmentally friendly and sustainable processing technology.Industrial use of this advanced technology can degrade the toxic pollutants in the environment into non-toxic or low-toxic substances,thereby reducing environmental pollution.In addition,photocatalytic technology can also reduce H₂O and oxidize CO₂,also Solar energy can be converted into hydrogen energy to achieve energy conversion and solve energy shortage problems.In this paper,a series of ZnO were prepared at different calcination temperatures and heating rates.A series of BiOX（X=Cl,Br,I）were synthesized by hydrothermal method,and a series of BiOX（X=Cl,Br,I）/ZnO heterojunction photocatalysts were synthesized by hydrothermal method.The synthesized products were characterized by a series of characterization methods,such as XRD and SEM and the photocatalytic activity and photostability of the samples were evaluated by photodegradation of azo dyes MO,4-NP and 1,4-DHP.The photocatalytic mechanism of the synthetic samples was investigated by active species trapping experiments.The main research contents of this thesis are as follows:A series of ZnO were prepared at different calcination temperatures and heating rates.The prepared ZnO nanostructures were characterized by XRD,SEM,XPS and DRS.The catalytic activity of ZnO was evaluated by photodegradation of azo dyes MO and 4-NP.Comparing photochemical stability and photocatalytic mechanism by photodegradation of MO,it was found that ZnO prepared at a calcination temperature of 300°C and a heating rate of 1°C/min had the highest photocatalytic activity,and the photocatalytic activity of ZnO was changed by calcination temperature and heating rate,but has little effect on photocatalytic stability and photocatalytic mechanism.Regardless of the preparation conditions of the ZnO photocatalyst,·OH^-,h⁺and·O₂^-are involved in the photodegradation process.A series of BiOX（X=Cl,Br,I）were synthesized by different hydrothermal methods and different halogen sources.The photocatalytic activity of BiOX prepared by different hydrothermal methods was evaluated by degrading the organic compound 1,4-DHP under irradiation of visible light.It was found that BiOBr prepared by hydrothermal-freeze drying method has the highest photocatalytic activity and good stability.In the process of degrading 1,4-DHP,the main active species is·O₂^-、h⁺and·OH.A series of BiOX（X=Cl,Br,I）/ZnO were synthesized by hydrothermal-freeze drying method and various amount of ZnO in the system.The photocatalytic activity of the prepared BiOX/ZnO was evaluated by degrading the organic compound1,4-DHP under irradiation of visible light.It was found that BiOBr/ZnO-1 and BiOI/ZnO-4 have better photocatalytic activity,but BiOI/ZnO-4 has the best photocatalytic performance.BiOBr/ZnO-1 and BiOI/ZnO-4 are very stable under visible light.In the process of degradation of 1,4-DHP by BiOBr/ZnO-1,the main active species is h⁺.In the process of degradation of 1,4-DHP by BiOI/ZnO-4,the main active species are h+and·O₂^-....