MnO₂ Catalyzed Ozone Oxidation Combined With Ceramic Membrane Separation For Wastewater Treatment

Catalytic ozone oxidation technology can be used for the rapid degradation of various organic pollutants and the selection of inexpensive,efficient,and stable catalysts is a key aspect of this technology.However,most manganese dioxide catalysts have low ozone catalytic activity due to their small specific surface area,pore volume,and pore size,resulting in low active site exposure.The catalytic activity of manganese dioxide catalysts can be effectively improved by using mesoporous materials with large specific surface area,pore volume,and pore size as templates for the preparation of mesoporous manganese dioxide.The catalytic ozone oxidation and membrane separation technology can be combined to treat organic pollutants to achieve in situ degradation of pollutants.In this thesis,a high catalytic activity mesoporous manganese dioxide（S-Mn O₂）catalyst was prepared by the template method,and a ceramic membrane with catalytic ozone oxidation function was prepared by loading the manganese dioxide agent onto the ceramic membrane using the sol-gel method.The main contents and results are as follows:（1）The mesoporous manganese dioxide catalyst with loose porous structure was successfully prepared by the template method using mesoporous molecular sieve SBA-15 and Mn（NO₃）₂ solution as the template and precursor,respectively.As-synthesized S-Mn O₂ had a large specific surface area,pore volume,pore size,and abundant surface oxygen vacancies,allowing for more surface active sites exposure and easily reducible surface adsorbed oxygen.The catalysts were initially investigated for ozone catalytic performance using methyl orange and oxalic acid as target pollutants.The results showed that compared to manganese dioxide prepared without the template molecular sieve SBA-15,the S-Mn O₂ catalyst exhibited higher catalytic activity with the highest degradation rates of 98.37%for methyl orange and 92.96%for oxalic acid.The effects of changing the ozone flow rate,catalyst dosage,initial solution concentration,initial solution p H value,and adsorption time on the catalyst performance were investigated.The results showed that when the ozone flow rate was 1 L·min^-1,the catalyst dosage was 30 mg·L^-1,the initial concentration of oxalic acid was 1 m M,the initial solution p H value was 4.2,and the equilibrium adsorption after adding the catalyst for 60 min,the oxalic acid degradation rate and the COD mineralization rate were 98.5%and 91.6%,respectively.In addition,the performance of the mesoporous manganese dioxide catalyst was investigated in cycling experiments and under environmental conditions.The catalytic performance of mesoporous manganese dioxide is stable and maintains high activity,which is a very promising ozone catalyst.（2）To further investigate the degradation mechanism of oxalic acid using ozone oxidation catalyzed by mesoporous manganese dioxide,the free radical scavenging experiments and electron paramagnetic resonance spectroscopy was performed.It was demonstrated that the reactive radicals generated during the catalytic ozone oxidation process were hydroxyl radicals and superoxide radicals.The results of X-ray photoelectron spectroscopy and electrochemical analysis showed that mesoporous manganese dioxide had a lower average oxidation state,higher electron transfer capacity,and more surface oxygen vacancies or surface hydroxyl groups.These results indicated that the charge transfer occurred between the mesoporous Mn O₂ catalyst and the adsorbed ozone molecules.During this process,the surface oxygen vacancies not only acted as staging posts for receiving and transporting electrons but also accelerated electron transfer;besides,the ozone decomposition produced reactive radicals to degrade oxalic acid adsorbed on the catalyst surface.The Mn O₂ catalyst was loaded on the surface of the ceramic membrane using a sol-gel method,which resulted in a flatter and more homogeneous surface.The results of the contact angle test indicated that the hydrophilic properties of the Mn O₂-loaded ceramic membrane were enhanced,allowing better separation of organic matter from water in wastewater.The catalytic performance of the Mn O₂ loaded ceramic membranes showed that the catalytic performance of the Mn O₂ loaded ceramic membranes with a size of 100×100 mm was increased by 23%compared to the oxalic acid degradation rate of the ceramic membrane support layer at an ozone flow rate of 1 L·min^-1 and an initial oxalic acid concentration of 1 m M.These results indicated that the catalytic performance of the ceramic membranes was significantly enhanced blooding Mn O₂,and therefore the combination of catalytic ozone oxidation and membrane separation technology can effectively treat organic pollutants.The mesoporous Mn O₂ catalyst prepared in this work can effectively improve the removal efficiency of organic pollutants from wastewater,which provides a reference for the promotion of manganese dioxide catalyst-catalyzed ozone oxidation in wastewater treatment.