Crystal Surface Defects, Oxygen Species And Bactericidal Property Of Metal Oxides

Samples of nano-MgO with varying particle sizes were prepared by four different methods using Mg(NO)·6HO, NaCO, urea and ammonia as raw materials and characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), low temperature N adsorption-desorption measurements and FT-IR spectroscopy. Bactericidal experiments with Bacillus subtilis var. niger and Staphylococcus aureus were carried out using as-synthesized nano-MgO samples and the bactericidal mechanism was also investigated. The results showed that the bactericidal efficacy of nano-MgO increases with decreasing particle size. The bactericidal efficacy of the samples was compared with that of TiO, a common photoactive bactericidal material. The nano-MgO has better bactericidal activity, both when used directly and as an additive in an interior wall paint. Furthermore, nano-MgO is active even in the absence of irradiation. The surface defects and active oxygen species produced on nano-MgO were researched by EPR. The bactericidal performances to S. aureus and B. subtilis by OH and O produced in nano-MgO solution were also reviewed respectively in order to analysis the bactericidal mechanism. The samples were characterized by such measurements as TG-MS, XPS, FT-IR and SEM, and the results showed that there is Fs colour centers on the surface of nano-MgO, the O stably absorbed on top of a four-or three-coordinated Mg ion at the defects produced on the corners and edges of nano-MgO. The mechanism of bactericidal activity of nano-MgO has been investigated. High concentrations of highly active superoxide ions were generated on the surface of the nano-MgO particles, which can react with the peptide linkages in the cell wall of bacteria or spores and thus destroy them.MgO-AlO composites with different sizes, different MgO dispersal and different crystal defects were controllably prepared by MgAl-CO-LDHs precursor. Bactericidal experiments with B. subtilis and S. aureus respectly were carried out using as-synthesized MgO-AlO composites and the bactericidal mechanism was also investigated. EPR results showed that there are Fs and Fz colour centers on the surface of MgO-Alo composites, and the O weakly adsorbed on top of a five-coordinated Mg ion at the planar face of the MgO-AlO composites. Bactericidal experiments results showed that MgO-AlO composites shows great bactericidal performance to S. aureus and the efficacy can reach 99%, and its efficiency against B. subtilis increases with decreasing particle size. The sample prepared by calcining precursor MgAl-CO-LDHs with 4 of Mg/Al mole ratio at 500℃can produce more superoxide O and show best efficacy against B. subtilis. The wall paints, HIPS and ABS, modified by MgO-AlO composites, can also show great bactericidal efficacy against bacteria and spores.MgO-ZnO-AlO and MgO-CuO-AlO composites, controllably prepared by calcining the precursors MgZnAl-CO-LDHs and MgCuAl-CO-LDHs, were used for bactericidal experiments and mechanism analysis and also characterized by measurements XRD, EDX, EPR. Results showed that the metals in composite oxides are highly dispersed and the defects on surface of crystal can lead to active superoxide O. Composite metal oxides have great bactericidal efficacy against S. aureus. The bactericidal efficiencies against B. subtilis were improved with the content increase of MgO in MgO-ZnO-AlO composites. The efficacy of MgO-CuO-AlO against B. subtilis increased greatly under the coordination effect between CuO and MgO when the molar ratio of Mg/Σ(M) is 0．25．The kinetics of the bactericidal action of nano-MgO and MgO-AlO composites against B. subtilis were investigated. The results show that the process of bacterial death followed first-order reaction kinetics. The activation energy (Ea) and frequency factor (A) can be calculated by Arrhenius formation k = Ae with changing the reaction temperatures. The Ea and A of the bactericidal action of nano-MgO against B. subtilis was 3．47×10J·mol and 2．51×10s respetcively when temperature was form 42℃to 26℃; while the Ea and A was 2．171·mor and 1．59s respetcively when temperature was form 26℃to 18℃. The Ea and A of the bactericidal action of MgO-AlO composite against B. subtilis was 2．47×10J·mol and 2．10×10s respetcively when temperature was form 42℃to 18℃.