Preparation And Mechanism Of Nano-sized Catalyst For Advanced Oxidation Process

Oxidation reaction is one kind of chemical reactions and it plays an extremelyimportant role in theoretical research and industrial chemistry. But harsh conditions,such as high temperature or pressure, were required in many oxidation reactions andlead to the increase of cost and energy. So it is imperative to develop materials which couldcatalyze oxidation reactions under normal temperature and atmospheric pressure. Amongvarieties of materials, nano-sized metallic oxides were widely researched because of its easygetting, low cost and facile synthesis and used to catalyze many oxidation reaction.In this paper, MnO2, Ag/Cuox-HCHO, MnO2/CuO were synthesized and applied tocatalyze corresponding oxidation reactions. Interactions among catalysts’ structures, oxygensources and substrate were studied; active species and active site were explored; mechanismand reaction path were also studied. MnO2was applied to catalytic ozonation reaction andspecial Mn-O bonds which prior to react with ozone were obtained. This provide an insightinto the microscopic reaction mechanism of materials which contain manganese.Ag/Cuox-HCHO was also used to catalyze ozonation reaction. Coexistence of copper andsliver enhanced the chemical and reaction stability. What’s more, it solved the problem ofmetal ion leaching in the reaction process. MnO2/CuO had both peroxidase-like andoxidase-like activity and applied in the quantitative detection of human cancer cells in nearneutral environment. MnO2/CuO which was used in Fenton reaction resolved the narrow pHrange of traditional Fenton catalysts and widen the operating environment of Fenton reaction.Otherwise, MnO2/CuO did not contain iron and enriched the diversity of heterogeneouscatalysts for Fenton reaction.MnO2with different crystalline phases were prepared by simple hydrothermal method.Compared with ozonation alone, MnO2could catalyze the degradation of phenol in ozonationruns. But different crystalline phases behaved differ. Since that α-MnO2, β-MnO2andγ-MnO2had good abilities in decomposing ozone, the difference of structure was responsiblefor the ozonation activities: The existence of active oxygen on the surface of α-MnO2had anacceleration on the activity, while manganese and corresponding oxygen were also a factorwhich result in the ozonation activity for the three catalysts. What’s more, special Mn-Obonds were sensitive to ozone, and they were the active sites. The special bonds were Mn-Obonds perpendicular to the direction of the [MnO6] octahedral double chains of α-MnO2,Mn-O bonds in the [MnO6] octahedral frameworks of β-MnO2and Mn-O bonds belonging topyrolusit type structure of γ-MnO2. Otherwise, catalytic activities were positive related totheir abilities in electron transfer on the surface.Another composite Ag/Cuox-HCHO which was synthesized by the assistance of methyl aldehyde also exhibited good catalytic ozonation activity; Lewis acid site was proved as thecatalytic active site; this catalyst can promote the decomposition of ozone, and Cu, Ag, Cu2Owhich were reduced state can be oxidized by ozone thus result in the oxidation of catecholand hydroquinol; Ag/Cuox-HCHO had better activity than catalyst which were composed bycopper or sliver only that copper and sliver had synectic effect to reach better performance;otherwise, Ag/Cuox-HCHO was very stable and leached less metal ion compared withCuox-HCHO; introduction of sliver not only enhanced the catalytic activity but also improvedthe stability in reaction.MnO2/CuO which was synthesized by oxidation-deposition method exhibited bothoxidase-like and peroxidase-like activities. Using TMB as substrate, its Michaelis constantwas7.2260×10-8M/s, and its maximum rate was0.0274mM which means a rather goodenzyme-like activity. Surface bonded hydrogen radical was proved as the active specie andsurface hydrogen as well as bulk metal atoms was the active site, and oxygen in the solutionwas oxygen source when MnO2/CuO exhibited oxidase-like activity, it behaved better inacidic condition but still had activity in neutral condition. Terminals of the reaction werepositive related to catalyst doses and concentration of hydrogen peroxide when MnO2/CuObehaved as peroxidase-mimic. Using chitosan and folic acid, the biocompatibleFA-CTS-MnO2/CuO was applied to detect human cancer cells A549and the detectionlimitation was as low as2000cells per well.MnO2/CuO also had Fenton-like activity, and it can catalyze the degradation ofnitrobenzene as near neutral condition. When catalyst doses was0.20g/L and hydrogenperoxide was0.5M, it behaved better. The activity rise with increase of temperature, and itbehaved best when pH was5.0. Active species were surface bonded hydrogen radical andhydrogen radical in bulk solution also did some contribution. Surface hydrogen as well asmetal atoms on the surface was the active site. By the redox cycle of Cu(Ⅰ)/Cu(Ⅱ) andMn(Ⅲ)/Mn(Ⅳ), hydrogen radical was generated to oxidase nitrobenzene. Ramanspectroscopy also supported that copper and manganese both react with hydrogen peroxide.The activity still maintained90%after four successive usage experiment. This revealed itspotential in practical application in near neutral condition.