Research On Molecular Oxygen Activation By Tio_2-x@C Materials Based On Interfacial Engineering

It is of much importance for the cycle of molecular oxygen in the world of nature.Whether in the metabolism of organisms or in all kinds of oxidation process like aerospace,the activation and utilization of molecular oxygen have irreplaceable research value.Molecular oxygen is abundant in the air?21%,volume fraction?,which could be the purest and greenest oxidant potentially.However,the ground state of oxygen molecular is too stable and difficult to directly join in the reaction on account of the triple state with spin-paralleled electrons,thus the generation of ROS?Reactive Oxygen Species?from the activation of O₂ is necessary.This thesis focused on the research of molecular oxygen activation method and constructed the absorption-activation TiO_2-x@C system based on the adjustment of surface/interface status.The ability,the pathways and mechanisms of O₂ activation and the universality of the system were studied in detail.The main contents are as follows:1.Research on activation of O₂ by TiO_2-x@C materials with different amounts of oxygen vacanciesTiO_2-x@C materials with different oxygen vacancies amounts were synthesized by different calcination temperatures with TiO₂-P25 and glucose as precursors and the ability of O₂ activation by TiO_2-x@C materials was studied qualitatively and quantitatively.The H-P25-850 ^oC@C sample?the calcination temperature was 850 ^oC?had the highest oxygen vacancies concentration?17.5%?and the highest production rate of ROS?Superoxide radicals and Singlet oxygen?.Meanwhile,the ROS could be applied into the non-light pollutant degradation,electrochemical oxygen reduction,solvent-free ethylbenzene oxidation and cancer therapy.In addition,Ti³⁺and O_v ?Oxygen vacancy?were proved to exist in the TiO_2-x@C materials and the surface carbon layer and oxygen vacancy were formed simultaneously during the high-temperature reduction.And the interaction between the surface carbon layer and oxygen vacancy was so close that it could be protector of the localized electrons in the vacancies thus to activate the oxygen molecules.2.Research on the mechanism of molecular oxygen activation by TiO_2-x@C materialsTiO_2-x@C materials with various surface/interface states?stoichiometric surface,surface with oxygen vacancy and carbon-coated surface with oxygen vacancy?were constructed,with which the ability of O₂ activation was studied carefully.?1?On the stoichiometric TiO₂ surface?ie,calcined in the air?,the molecular O₂ would only have very weak physical absorption far away from the activation.?2?On the TiO₂ surface with oxygen vacancies?ie,calcined in the H₂?,the surface oxygen vacancies theoretically could be the active sites for O₂ activation while it did not happen under mild conditions.With the participation of H₂O,the O₂ and H₂O would react with proton exchange to form terminal OH groups and thus to cause the occupation of oxygen vacancies,which would make the O₂ activation ability lost.?3?On the TiO_2-x@C surface with carbon layer and oxygen vacancies,the absorption of H₂O could be effectively inhibited by the surface carbon layer as a protector and stabilizer and the localized electrons within the oxygen vacancies could be protected and serve for the molecular oxygen activation.Besides,the behaviors of O₂ and H₂O molecules separately and jointly were simulated by DFT calculation,which confirmed the protection role of the surface carbon layer.3.Research on the interface regulation of TiO_2-x@C materialsThe effect on the O₂ activation with different surface/interface status was studied by the adjustment of different kinds of precursors?TiO₂ with different crystal phases or faces and carbon-layer precursors?.The formation of the surface carbon layer was studied preliminarily.Also,the universality of the TiO_2-x@C materials was expanded into some other metal/non-metal oxides and it had shown some excellent performance of molecular oxygen activation as long as the specific requirements of these oxides.It would bring some new insights into the future design of more accurate structure for the O₂ activation.