Preparation And Photocatalytic Properties Of SnO₂ And NiO/SnO₂ Nanocomposites

Photocatalytic oxidation is a green technology,which has a good application prospect in removing degradation-resistant organic pollutants in water.As an n-type semiconductor,Sn O₂has become an ideal material for eliminating organic pollutants in water because of its strong oxidation properties.In this thesis,Sn O₂nanoparticles were prepared by a facile low-temperature hydrothermal method,and their photocatalytic properties were improved by combining with Ni O.The main research contents and results are as follows:Using orthogonal experiment method,samples of Sn O₂nanoparticles with rutile structure were prepared by low-temperature hydrothermal method under different process parameters.Then,Malachite green（MG）solution was used to simulate organic pollutants,and the degradation rate constant of the samples to MG under UV irradiation was used as the key index to optimize the preparation process parameters of Sn O₂nanoparticles.The optimal process parameters obtained by range analysis are as follows:reaction temperature 95℃,reaction time 5 h,calcination temperature 550℃,and calcination time 3 h.The Sn O₂nanoparticles prepared under the optimized process parameters are also rutile structure,the particle diameter is about 10 nm,and show better degradation effect on MG under UV irradiation.Based on the Sn O₂nanoparticles prepared under optimized process parameters,Ni O/Sn O₂nanocomposites with different Ni O contents（molar ratio[Ni]/[Sn]=1:4,1:2,1:1,2:1）were further prepared by low temperature hydrothermal method.The morphology,microstructure,and composition of the composites were characterized,and the results showed that the Sn O₂nanoparticles and the Ni O nanoparticle combined well,and the Sn O₂nanoparticles deposited on the Ni O nanosheets and formed p-n heterojunction.Photocatalytic performance test showed that the photocatalytic activity of the composites was improved,and the best photocatalytic effect was obtained at the molar ratio of[Ni]/[Sn]=1:2.Taking the Ni O/Sn O₂nanocomposite with molar ratio[Ni]/[Sn]=1:2 as an example,the effects of different experimental parameters on the degradation rate of MG were explored.The results showed that the photocatalytic degradation of MG was the best when p H=7,dye concentration is 10 mg/L and the catalyst dosage is 10 mg.Free radical trapping experiments show that the activity order of several substances which play important roles in the photocatalytic process is·O₂^->·OH>h⁺.In addition,repeatability tests show that the composite has good reusability and stability.The photocatalytic degradation mechanism of MG was discussed,and it is concluded that the separation and transfer of the electron-hole pairs generated by p-n heterojunction formed between Ni O nanosheets and Sn O₂particles is the main reason for the enhancement of photocatalytic performance of the Ni O/Sn O₂nanocomposites.