Preparation of highly dispersed MgO and its bactericidal properties

Samples of layered double hydroxides (LDHs) were prepared by a method involving separate nucleation and aging steps recently developed in our laboratory, using varying Mg²⁺] / Al³⁺] ratios and different aging conditions. The samples were characterized by X-ray diffraction (XRD), FT-IR spectroscopy and laser granulometry. The results showed that LDHs with different particle sizes could be obtained by controlling the reaction temperature and degree of supersaturation. Calcination of these materials affords mixtures of highly dispersed MgO and mixed metal oxides. Bactericidal experiments against Bacillus subtilis var. niger and Staphylococcus aureus were carried out using materials formed by calcination of the LDHs at 500 ^○C. The mechanism of bactericidal activity was also investigated. It is known that MgO is very readily hydrated and that reaction with dissolved oxygen affords superoxide anions O₂^-, which attack the secondary amide structure of proteins leading to destruction of the bacteria. The bactericidal activity of the MgO increases with specific surface area because this leads to an increased number of surface hydroxyl groups and higher concentrations of O₂^- in solution. The bactericidal ability of MgO therefore increases with decreasing particle size.