Study On The Doping, Composite And Properties Of Nano Magnesium Oxide

Nano-MgO is a new type multifunction inorganic material, which exhibits uniqueoptical, electric, magnetic, thermal and mechanical properties. Doped MgO and MgOcomposites have wide application prospect in many fields, especially in antibacterialmaterials and optical films. Doping could cause many kinds of lattice defects, whichwould modify the physical and chemical properties of matrix. Li+ion, whose ion radius isclose to Mg²⁺ion, was chose to dope with MgO and the effect of Li-doped on the structure,morphology and antibacterial properties of nano-MgO were studied. The mechanism forLi-doping to enhance the antibacterial properties of nano-MgO was preliminarilydiscussed. Meanwhile, nano-MgO/polyimide composites which have good compatibilitywere prepared without any coupling agents or surface modifiers. The structure and opticalproperties were studied and the coordination mechanism between the carbonyl group ofpolymers and Mg atom was explored. This work mainly includes the following aspects:Li-doped MgO nanopowders were prepared by a sol-gel method using magnesiumnitrate hexahydrate, lithium nitrate as starting materials and citric acid as complexingagent. The precursors are amorphous, which demonstrates lithium doping has no obviousinfluences on the phase structure of the precursors. After being calcinated at600°C for1h,a magnesia phase with periclase structure （JCPDS87-0653） was found in all nanopowders.Notably, there is an unknown diffraction peak appeared at29.3°in all Li-doped samples,which may be due to the incorporation of Li ion into the MgO matrix. The diffraction peakintensity and crystallite size of MgO phase increased with an increase of lithium content,which indicates that lithium doping has an effect of facilitating the crystal growth andcrystallization of MgO. When the lithium content increases to10%, some characteristicpeaks from Li₂CO₃phase are detected in the scanning range.Escherichia coli （E. coli, ATCC25922） were selected as a model to evaluateantibacterial properties of the as-obtained samples and the minimum inhibition concentration （MIC） and24h bactericidal rate were used to evaluate the antibacterialactivities of the as-obtained nanopowders. The results show that the sample of5%Li hasthe best antibacterial activity in these samples, which MIC value is500ppm andbactericidal efficacy against E. coli with the concentration of500μg/mL is99.99%. Thepromotion effect of lithium doping could be attributed to the change of oxygen vacancyfrom powders and the pH value of powder solutions, which are in favor of the generationand stabilization of active oxygen （O₂^-）. It is well known that the doping of a low valencyion （Li+） in the oxide （MgO） host lattice will favor the formation of oxygen vacancy,which has strong tendency to adsorb and activate oxygen to generate O₂^-. On the otherhand, the stability of O₂^-increases with increasing pH value in the medium. As for thesample of10%Li, the antibacterial activity reduced, which can be due to the fact that theLi₂CO₃phase formed and the MgO content is relatively lower in powders.Nano-MgO/polyimide composites were successfully fabricated via an in situ sol-gelpolymerization technique. The MgO nanoparticles were well dispersed in the polymermatrix due to the coordination between the carbonyl group of polymers and Mg atom, andthe as-prepared composites exhibited excellent optical transparency in the visible regionand good UV-shielding properties in the UV region. In addition, the thermal stability ofthe composites is good enough for the practical application below the temperature of300°C.