Surface-modified Metal Oxides Catalyzed Ozonation To Degrade Pollutants

As more and more organic pollutants are found in the water environment,there is a growing concern about how to remove them cost-effectively.Conventional water treatment technologies are unable to completely remove organic pollutants,but ozone oxidation has been found to be effective for their removal,mainly due to the introduction of catalysts that further promote the decomposition of ozone molecules to generate free radicals with strong oxidizing properties,such as hydroxyl radicals(^·OH)and superoxide radicals(O₂^·-).The metal oxide catalyzed ozonation process based on single-site redox has a rate limiting step,which suppresses the activity and greatly limits the practical application of multiphase catalytic ozonation technology.To address this bottleneck,catalysts with dual reaction centers were prepared in this thesis by lattice doping of metal oxides with transition metals.The morphological structure and chemical composition were characterized and analyzed by XRD,TEM and XPS techniques,and the activity and stability of the catalysts were investigated by activity evaluation using ibuprofen as a contaminant,and then the interfacial reaction mechanism was revealed by EPR and electrochemical techniques.The main research contents are as follows:(1)The catalyst FT-A-1 DRCs were prepared by using metal oxide?-Al₂O₃ as the substrate material and lattice doped with transition metal species Fe and Ti.The morphological structure and chemical composition were characterized by XRD,TEM and XPS techniques,which demonstrated that the lattice substitution of Fe and Ti for Al,forming surface electron-poor microregions(electron-rich Fe microcenters and electron-deficient Ti microcenters),which exhibited excellent activity and stability for the removal of a series of refractory organic pollutants such as ibuprofen.The interfacial reaction mechanism was revealed using EPR and electrochemical techniques.It was found that during the catalytic ozonation process,O₃/H₂O was directed to be reduced in the electron-rich microcenters to produce^·OH,while the pollutants could be oxidized in the electron-deficient microcenters as electron donors,providing electrons to the reaction system continuously.This reaction process utilizes the pollutant's own energy to achieve dual pathway degradation of the pollutant(^·OH attack and direct electron donor),breaking through the rate limiting step of the metal oxide catalytic ozonation process.(2)To further enhance the construction of dual reaction centers,the catalyst Cu-ZnO was prepared by doping its lattice with Cu elements using ZnO,a representative of the more reactive group IIB elements,as the substrate material,which leads to the formation of electron-rich Cu microcenters and electron-deficient Znmicrocenters due to the difference in electronegativity of Cu and Zn.A multiphase catalytic ozone oxidation system based on Cu-ZnO was established to improve the degradation and mineralization rates of ibuprofen(IBU)in a wide pH range.It was found that O₃/OH^-on the electron-deficient Zncenter would replace the electron donor when the pollutant was added,and this phenomenon not only promoted the electron-rich Cu microcenters to generate more^·OH to attack the pollutant,but also degraded the pollutant by oxidation due to its own electron supply.The synergistic effect of the above two pathways accelerates the degradation efficiency of pollutants.At the same time,with the addition of humic acid(HA)for directional adsorption,the combination with pollutants completely replaces O₃/OH^-as an electron donor,promoting the utilization of O₃ in electron-rich Cu microcenters and further accelerating the removal efficiency of pollutants,not only attacking the existence of a rate limiting step for the cyclic reaction between Meⁿ⁺and Me^(n+m)+on metal oxide surfaces,but also providing a model for multiphase catalytic ozone oxidation for the treatment of real water reference.And it also shows good catalytic performance for the treatment of actual printing and dyeing wastewater by ozone oxidation technology.