Study On The Synthesis, Characterization And Photocatalytic Properties Of Mg_1-x（Zn/Cu）_xAl₂O₄ Spinel Oxides

Photocatalytic technology provides a new, environmentally friendly and efficient method for the degradation of pollutants.As a kind of new type of photocatalytic materials, spinel type composite oxides have the advantages of high photochemical stability and high recycling efficiency. Mg Al₂O₄ as a type of spinel group minerals has the advantages of high melting point, thermal expansion coefficient, thermal conductivity, good thermal shock resistance, anti erosion ability of alkali strong advantages.Study on effects of transition metal substituted spinel structure and photocatalytic performance has important significance.In this experiment, NH₃·H₂O and Na OH were the precipitation agent, and Mg Cl2·6H₂O,Al Cl₃·6H₂O were raw materials. Mg_1-x（Zn/Cu）_xAl₂O₄ was made with different calcinations temperature and characterized by X-ray diffraction, UV-Vis diffuse reflection spectrum, and transmission electron microscopy, thermal gravimetric and differential scanning calorimeters and so on. Finally, spinel nanoparticles were evaluated by monitoring the degradation of methylene blue under UV light with mercury lamp.Mg Al₂O₄ can be formed at 700℃ with different precipitation agent like NH₃·H₂O and Na OH. With the increase of the calcinations temperature, crystallinity of the Mg Al₂O₄ was increased and degradation rate was decreased. Mg Al₂O₄ with Na OH as the precipitation agent has a smaller energy gap and methylene blue degraded above 80% within 4 hrs with Mg Al₂O₄ that calcinated at 700℃.(Mg_1-xZn_x)Al₂O₄ spinel nanoparticles with x= 0.05, 0.10, 0.15 and 0.20 were prepared. With different amounts of Zn²⁺ substitutions, Mg Al₂O₄ strcture hasn’t been destroyed. When x=0.05 and x=0.01, the degradation rate has decreased. With the increases in the amounts of Zn²⁺ substitutions,the effects of Zn²⁺ additions on the photocatalytic activities become gradually predominant, leading to the increases in the degradation rates.(Mg_1-xCu_x)Al₂O₄ spinel nanoparticles with x= 0.05, 0.10, 0.20 and 0.30 were prepared. With different amounts of Cu²⁺ substitutions, Mg Al₂O₄ strcture hasn’t been destroyed.UV-Vis diffuse reflection spectrum shows that the absorption edge has moved to infrared region. However, the photocatalytic performance of Mg_1-xCu_xAl₂O₄ decreased with the increase of the Cu²⁺ substitutions.At last, photocatalytic mechanism of Mg_1-x（Zn/Cu）_xAl₂O₄ has been studied.Results of 27 Al MAS-NMR spectroscopy analysis and the first principle total density of state calculations revealed that this was probably due to the addition of Zn²⁺ decreasing the degree of Al³⁺ ions inversionover the sites of tetrahedral and octahedral coordination. With the increases in the amounts of Zn²⁺ substitutions, the effects of Zn²⁺ additions on the photocatalytic activities become gradually predominant, leading to the increases in the degradation rates.