Investigations On The Spinel-Structured Photocatalyts: Synthesis And Their Performances In Toluene Degradation

As an important class of inorganic materials, spinel-structured composite metal oxides are widely used in high temperature resistant materials, photoelectric materials, magnetic materials, sensing and catalysis, and many other fields. It is very important to control the particle size, morphology and chemical composition of the composite metal oxides and study the relationship between the microstructure and photocatalytic activity for the application of photocatalysis technology in environmental purification. The current thesis mainly focused on the fabrication of some photocatalysts with spinel structure, i.e., zinc aluminate, cobalt ferrite, nickel ferrite, and Ag-loaded composite metal oxides. The author compared and discussed the effects of their particle size, morphology and chemical composition on the photocatalytic degradation of toluene, while the photocatalytic reaction mechanisms were studied in detail by in-situ FTIR.Cubic spinel phase ZnAl2O4 nanorod materials were prepared by hydrothermal method through regulating the pH of the precursor solution. When the pH of the precursor solution is 6, the obtained ZnAl2O4 nanorod material exhibited the best performance in the photocatalytic degradation of toluene. By comparing the degradation efficiencies of toluene with different amounts of Ag dopant, it was shown that 1 wt% Ag-loaded sample had the best performance for photodegradation of toluene. Then rectangular-shaped and irregular-shaped cubic spinel ZnAl2O4 particles were prepared by an NH4·Ac precursor based hydrothermal method and urea or citric acid based method, respectively. Their structures and the photocatalytic degradation of gaseous toluene were compared. The results showed that the ZnAl2O4 particles synthesized by a NH4-Ac precursor hydrothermal method aggregated together and formed porous rectangular-shaped superstructure, which possesses a large surface area, mesoporous structure and a monomodal pore size distribution. Under UV light irradiation, the rectangular-shaped ZnAl2O4 particles had the highest photodegradation efficency for gaseous toluene. Moreover, distinct deactivation was not observed for the ZnAl2O4 catalysts.Then, the thesis developed NiFe2O4 and CoFe2O4 materials by a simple and environmentally benign wet-chemical route. The "timber-like" CoFe2O4 and "brick-like" powders successfully prepared at different calcination temperatures possess spinel-type crystalline structure. The structure, morphology and photocatalytic properties of the samples were studied. The porous rod-like CoFe2O4 and NiFe2O4 particles aggregated together and formed "brick-like" and "timber-like" superstructure. They showed excellent photocatalytic degradation activities under visible light irridiation. Finally, silver was successfully loaded into the "timber-like" CoFe2O4 and "brick-like" NiFe2O4 powders by impregnation method. Through the comparative study on the photocatalytic degradation of toluene using these catalysts, it was indicated that the Ag/CoFe2O4 composite material had a higher photodegradation efficency under visible light irradiation.