| The organic pollution in air or water harms the human’s health and affects the human’s survival, and thus the elimination of trace organic compounds in air or water is a common challenge facing the human society. Manganese dioxide has a variety of crystal phases, and manganese dioxide with different crystal phases is also diverse in thermal catalytic oxidation property and photo catalytic property, which has become an increasingly significant topic in recent years. Loading gold or silver on manganese dioxide can change the surface adsorption property and electronic property of the catalysts. The study of gold or silver catalysts supported on manganese dioxide for eliminating trace organics in air under thermal catalytic condition or eliminating trace organics in water under visible light irradiation has important theoretical and practical significances.In this study, three types of MnO2of different phases were synthesized based on different methods, and then series of Au/MnO2and Ag/MnO2catalysts were prepared via the metal colloid deposition method. The catalysts were characterized by the X-ray diffraction(XRD), the scanning electron microscopy(SEM), the transmission electron microscopy(TEM), the nitrogen adsorption-desorption, and the UV-vis DRS. In addition, the thermal catalytic performances for the oxidation of trace formaldehyde in air and the oxidation of trace dimethylbenzene in air as well as the photocatalytic performance for the degradation of trace methylene blue in water under the irradiation of visible light of the catalysts were investigated. The content and results of this study is as follows: 1. Three types of manganese dioxide of ε-MnO2, α-MnO2and δ-MnO2with different morphologies were synthesized using manganese sulfate and potassium permanganate as raw materials. And then Au/MnO2and Ag/MnO2catalysts were prepared using the three types of manganese dioxide as supports by the metal colloid deposition method. It was found that the gold nanoparticles highly dispersed on the surfeces of MnO2, and the particle sizes were distributed between5-10nm Moreover, morphologies of MnO2were preserved well enough.2. The gold or silver catalysts supported on MnO2exhibited superior catalytic performances for the oxidation of trace formaldehyde in air. The gold catalysts were better than the silver catalysts, and the catalysts loading with3(wt.)%gold exhibited the best activities. The sample of the Au/a-MnO2loading with3(wt.)%gold could completely oxidize the trace formaldehyde in air with a concentration of200ppm to CO2and H2O at a space velocity of40000mL/(g· h), and a reaction temperature of110℃.3. In the thermal catalytic oxidation of xylene, the activities of the gold or silver catalysts were better than those of the corresponding supports, and those of the gold catalysts were better than those of the silver catalysts. However, the oxidation of xylene has higher reaction temperature than that of the oxidation of formaldehyde at the same conversion for the same catalyst. The catalyst loading with3(wt.)%gold exhibited the best activity at a space velocity of40000mL/(g· h) and a concentration of xylene of400ppm, the conversion reaching25%at100℃and reaching80%at400℃.4. During the degradation of methylene blue under the visible light irradiation, it was found that the three types of manganese dioxide exhibited excellent photocatalytic performances, and the δ-MnO2had the highest photocatalytic activity. The degradation rate attained to85%within10minutes at an initial concentration of25mg/L of the methylene blue. However, the photocatalytic activities of Au/MnO2and Ag/MnO2catalysts were inferior to manganese dioxide. This was due to the rapid decomposition of hydrogen peroxide to O2on these catalysts, resulting in the termination of the reaction. |
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