Oxygen Vacancy,morphology Control And Antibacterial Mechanism Of Magnesium Oxide Nanomaterials

MgO nanomaterials（nano-MgO）have wide applications in the antibacterial field.The antibacterial properties of nano-MgO are strongly related to their oxygen vacancies and morphologies.Fabrication of nano-MgO with rich oxygen vacancies and special morphologies possessing the advantage of high efficiency in antibacterial activity has important theoretical and practical value.In this thesis,we focused on the development of different strategies to control oxygen vacancies and morphologies on the nano-MgO surface to improve the active oxygen antibacterial and structural bactericidal properties.The main results are summarized as follows:（1）The nano-MgO with oxygen vacancies were prepared by an acid etching process.Compared with the untreated sample,the surviving E.coli colonies of acid treated nano-MgO（in the hydrochloric acid solution under p H=2 for 1 h）decreased from 120 to 54（10² CFU/m L）.The enhanced antibacterial activity was originated from the acid-etching effect.When nano-MgO surface were exposed to acidic solution,the deformation of surface lattice was easy to occur,and this process was accompanied by the formation of oxygen vacancies.The acid etching method could directly modify the surface of nano-MgO to expose more oxygen vacancies,which would promote reactive oxygen species（ROS）generation.Especially,·O₂^-was the crucial factor in ROS damage in comparison with·OH and H₂O₂.（2）The oxygen vacancies concentration of nano-MgO was carefully adjusted by varying the calcination temperature in the hydrothermal-calcination method.Moreover,the nano-MgO samples without impurity phase still maintained nanodisks shape similar to the precursors.Calcination of the precursor at 450°C could effectively enhance the antibacterial ratio of nano-MgO to above 99.9%at the concentration of 750μg/m L.The reasonable regulation of calcination temperature could increase oxygen vacancies of nano-MgO,which was beneficial in more·O₂^-production.When the amount of nano-MgO was higher than 2.0 mg/cm²,the non-woven fabrics prepared by a surface spray technology had the excellent antibacterial ability against E.coli,with the antibacterial ratio reached above 99%.（3）Compared with air atmosphere,the oxygen-deficient calcination could increase oxygen vacancies on nano-MgO surface,and the antibacterial ratio increased correspondingly（from64.8%to 93.2%）.The nano-MgO with abundant oxygen vacancies could induce production of ROS and increase the ROS level in E.coli,thus resulting in the inactivation of bacteria.Moreover,the abundant oxygen vacancies enhanced the hydrolysis of nano-MgO and production of massive OH^-.The alkali microenvironment around the nano-MgO surface was beneficial for the stabilization of ROS.（4）The antibacterial nano-MgO with rich oxygen vacancies were successfully prepared by Li doping and oxygen-deficient calcination strategy for the first time.The antibacterial ratio of nano-MgO at a very low concentration（100μg/m L）reached 99.6%against 10⁸ CFU/m L of E.coli.The superior antibacterial activity of nano-MgO has been achieved,mainly attributed to the high number of oxygen vacancies,which was boosted by the synergistic effects of calcination in oxygen-deficient systems and Li doping.Besides,the high basicity of nano-MgO facilitated the stabilization of ROS.（5）A novel chemical precipitation method was reported for the fabrication of the multilayer-blade nano-MgO.The rapid antibacterial activity of nano-MgO was significantly improved due to their special morphologies.The nano-MgO completely inhibited E.coli growth in 2 h.Moreover,tuning of oxygen vacancies concentration of the multilayer-blade nano-MgO by suitable P doping was feasible for the improvement of antibacterial efficiency.Based on the oxygen vacancies-mediated ROS generation of P-doped nano-MgO as well as the structural antibacterial effect,P-MgO-3 at a concentration of 100μg/m L displayed the high antibacterial activity against E.coli,with the antibacterial ratio reached approximately100%.