| As a new type of inorganic material, Nano-MgO has been extensively studied andutilized in many fields due to its excellent optical, electrical, magnetic and mechanicalproperties. Expectedly, Nano-MgO has also been shown a significant advantage inantibacterial field. Based on the unique antibacterial property and mechanism ofNano-MgO, in this paper doped MgO and MgO composites were prepared to improvethe antibacterial activity and to broaden the application areas of MgO. In our work, threedifferent metal ions (Li+, Zn2+, Ti4+) were selected to incorporate into MgO matrix andthe effects of different ion doping on the structure and morphology were studied. Theinfluence mechanism of different doping ions on the antibacterial properties of dopedNano-MgO was also discussed. Meanwhile, Ag/MgO composites were prepared using anew in-situ synthesis method. The influences of solvents and the sizes of MgO on thepreparation of the composites were explored; furthermore, the mechanism of in-situsynthesis and the antibacterial properties of Ag/MgO composites were investigated.Doped nanopowders were prepared by a sol-gel method using magnesium nitratehexahydrate, the dopant (LiNO3, Zn(NO3)2·6H2O or Ti(OC4H9)4) as starting materials andcitric acid as complexing agent. The results of XRD indicated that the metal ion dopinghas no obvious influences on the phase structure of the precursors. After being calcinatedat600℃, all nanopowders can be indexed to a magnesia phase with periclase structure(JCPDS87-0653). However, there are obvious differences in the intensity of diffractionpeaks because different ions may cause different effects on the formation of MgO crystal.Moreover, Li-doped MgO has the biggest size (about23.6nm) and a flake-like shape, asshown in the TEM image, but Ti-doped MgO has the smallest particle size. The analysisof XPS proves that Li doping promotes the generation of oxygen vacancies whereas Tidoping inhibits the generation of oxygen vacancies. But Zn doping has almost no effect onthe generation of oxygen vacancies. Escherichia coli (E. coli, ATCC25922) were selected as the test bacterium. Theminimum inhibition concentration (MIC) and24h bactericidal rate were used to evaluatethe antibacterial activities of the as-obtained nanopowders. The results showed thatLi-doped MgO has the lowest MIC value (500ppm) showing the best antibacterial activity,followed by MgO (550ppm). However, Ti-doped and Zn-doped MgO have relatively poorantibacterial activities. In addition, the bactericidal efficacy against E. coli of Li-dopedMgO with the concentration of500ppm is99.99%. The mechanism for the effect of iondoping is as follows. From the defect reactions, Li doping promotes the generation ofoxygen vacancies, and O－2can be generated by single-electron reduction from oxygenvacancies. Furthermore, O－2is stable in alkaline environment. And the increased pH ofLi-doped MgO can provide a more stable environment for O－2. Thus the enhancedantibacterial property of Li-doped MgO is attributed to the synergies of oxygen vacancyand basicity of nanopowders; However, Ti doping inhibites the generation of oxygenvacancies and the pH of Ti-doped MgO decreases, so the antibacterial property of thissample is relative weak. As for Zn-doped MgO, the pH is also relatively lower than pureMgO, so it exhibits the poorer antibacterial property.Ag/MgO composites were successfully fabricated via in-situ synthesis method, usingAgNO3and the prepared Nano-MgO as starting materials. The components of thecomposites were analyzed and confirmed by XRD, XRF and XPS. Moreover, theinfluences of solvents and the sizes of MgO during the preparation and the mechanism ofin-situ synthesis were discussed. To investigate the antibacterial properties of thecomposites, E. coli were still used as the test bacterium. The results show that adding asmall amount of silver, the MIC of MgO can be dropped from550ppm to100ppm. It canbe clearly seen that with the addition of silver, the antibacterial properties of Nano-MgOare greatly improved. |
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