Preparation Of Core-shell Structured MnO₂@SiO₂ Catalyst And Its Catalytic Properties For Atrazine Oxidation By Ozone

Heterogeneous catalytic ozonation（HCP）has been widely studied and paid attention to in the field of organic pollutant removal due to its environmental friendliness,simple technological process and high economic effect.However,the current catalytic performance of heterogeneous catalysts cannot meet the needs of actual water treatment.The research and development of highly efficient heterogeneous catalysts is a hot and difficult point at present.Different from the current research and development strategy of supported heterogeneous catalyst,the heterogeneous catalyst with core-shell structure is constructed in this thesis.With atrazine as the model organic pollutant,the catalytic performance and mechanism of the catalyst were systematically analyzed and discussed.The main contents are as follows:（1）core-shell structure manganese dioxide and silicon dioxide（MnO₂@SiO₂）catalysts were prepared by hydrothermal method and sol-gel method,and their morphology,structure and physicochemical properties were analyzed and characterized.The results shown MnO₂@SiO₂ was a uniformly dispersed nanorod-like core-shell structure.Its core wasα-Mno2 and its shell was amorphous Si O₂.Mn O₂ is connected to Si O₂ by Mn-O-Si bond.MnO₂@SiO₂ presented a mesoporous structure with a large specific surface area.（2）The oxidative degradation of ATZ by O₃ catalyzed by MnO₂@SiO₂ was systematically studied.The effects of reaction parameters（catalyst dose,O₃ concentration,ATZ concentration and p H）on ATZ degradation were studied.The correlation between MnO₂@SiO₂ catalytic activity and synergistic effect was analyzed.The stability and reusability of MnO₂@SiO₂ are tested and analyzed.The results show that under the best experimental conditions,the removal rate and mineralization rate of MnO₂@SiO₂ are96.5%and 36.1%,respectively.The synergistic effect of MnO₂@SiO₂ is the key to its high catalytic activity.MnO₂@SiO₂ has high reusability.After five consecutive cycles,the catalytic performance of MnO₂@SiO₂ only decreases by about 10%,and the surface morphology and crystal structure have no obvious changes.The results of ICP-MS test show that MnO₂@SiO₂ can effectively prevent Mn leaching.（3）The active substances produced in the system and their contributions were analyzed and determined by quenching experiment;The exposure of free radicals was calculated by chemical kinetics model.XPS was used to measure the valence state of the elements before and after the catalyst reaction to determine the active site of the catalyst.The intermediate product of ATZ degradation was determined by HPCL.The toxicity of ATZ and its intermediate products was analyzed by ECOSAR model.The results showed that·OH was the main active oxygen species degrading ATZ;MnO₂@SiO₂ can be effectively exposed and enriched·OH;Mn³⁺and oxygen vacancy（OVs）are the active sites that MnO₂@SiO₂ catalyzes the decomposition of O₃ to·OH.ATZ is degraded mainly by dealkylation,alkyl hydroxylation,alkyl oxidation and dechlorination;Compared with ATZ,the toxicity of the intermediate product was significantly reduced.