Study On The Performance And Mechanism Of Oxidation Degradation Of Methylene Blue In Water Based On Titanium-based Catalytic Membran

Organic pollutants such as methylene blue（MB）have the characteristics of refractory degradation and high biological toxicity.Peroxymonosulfate advanced oxidation process and electrochemical advanced oxidation process have been widely used in the treatment of organic pollutants in wastewater.However,the above-mentioned two technologies also have the disadvantages of low mass transfer efficiency and difficult recovery and separation from the system.In this study,a catalytic membrane system was constructed to study the performance and mechanism of MB degradation in response to the above problems.Aiming at the problem that the powder catalyst is difficulted to separate from the system,we constructed a Co₃O₄-Bi₂O₃-Ti catalytic membrane（CBO-Ti-M）to applied for removing MB via activating peroxymonosulfate（PMS）.Through the analysis of the characterization of the catalytic membrane shows that the main component of the CBO-Ti-M was Co₃O₄-Bi₂O₃（CBO）catalyst.The effect of PMS concentration and flow rate on the degradation of MB was investigated.Under the optimal experimental conditions,the degradation rate of MB could reach 98.7%.The reusability test showed that the pollutant removal efficiency of the CBO-Ti-M/PMS system remained stable during the four runs,and limited metal leaching was observed.The effects of inorganic ions（Cl^-,HCO₃^-）,humic acid（HA）as well as the water quality conditions（tap water and lake water）on the degradation performance of MB were studied.Based on quenching experiments,electron spin resonance（ESR）and in-situ open circuit potential（OCP）tests revealed that singlet oxygen and non-radical electron transfer pathways play a major role in the reaction.The possible degradation pathway of MB was proposed based on HPLC-MS analysis.Compared with the peroxymonosulfate advanced oxidation process,the electrocatalytic oxidation process has the advantages of not needing any chemical agent and no by-product.In this study,a Ti³⁺-doped TiO₂ porous membrane electrode（Blue TiO₂/Ti）was synthesized in situ on the base titanium membrane.The electrode was characterized and analyzed.The electrochemical analysis of the electrocatalytic performance of the Blue TiO₂/Ti electrocatalytic membrane revealed that the electrode has a higher oxygen evolution potential,a larger redox peak current,a lower resistance and a larger electrochemically active surface area.The effect of current density and flow rate on the degradation of MB was investigated,and the degradation rate of MB reached 99.5%under the optimal operating parameters of 0.5 m A/cm² and 0.8 m L/min.The stability test shows that the MB degradation efficiency can still reach 98.0%after30 hours of continuous operation.The effects of inorganic ions（Cl^-,HCO₃^-）,HA and the natural water quality conditions（tap water and lake water）on the degradation performance of MB were studied.The quenching experiment and the analysis of the salicylic acid product together proved that the·OH is mainly free radicals,which played the most important role to degradate MB present in the system.Combined with HPLC-MS,gas chromatography mass spectrometry（GC-MS）and the theoretical calculation of orbital-weighted ffunction,the possible degradation paths of MB were proposed.Both the CBO-Ti-M and Blue TiO₂/Ti catalytic membranes increased the mass transfer efficiency through the continuous flow mode and improved the degradation efficiency of MB.Compared with the CBO-Ti-M/PMS system,the Blue TiO₂/Ti electrocatalytic membrane system has the advantages of high degradation rate,without adding chemicals such as PMS to the water,and without any metal dissolution,but the CBO-Ti-M/PMS system does not require to apply voltage,reducing energy consumption.