Study On The Antibacterial Activity Of Zinc Oxide And Its Mechanism

The antibacterial activity, the production of active species and the effect of Cu2+doping for three kinds of ZnOs were studied in this paper.Antibacterial activities of three kinds of ZnOs were evaluated by comparing the zone of inhibition and the bactericidal rate, respectively. The effects of light excitation and morphology were investigated, and the results showed that all the three kinds of ZnOs (nano-scaled n-ZnO, commercial produced p-ZnO and tetra-needle-like T-ZnO) displayed antibacterial activity that ranked as T-ZnO, n-ZnO and p-ZnO, Further investigation demonstrated that morphology of ZnO exhibited a considerable influence on the antibacterial activity. The antibacterial activity of ZnOs under simulated sunlight was better than that in darkness, and all of them displayed higher efficiency against E. coli than that against S. aureus.Iodometric method combined with spectrophotometric analysis was applied to the quantitative evaluation of H2O2 in ZnOs suspensions. Effect of excitation conditions, reaction time and morphology of ZnOs on the production of H2O2 were investigated, and the results showed that the amount of H2O2 from the related three kinds of ZnOs basically linearly increased with extending reaction time, and were ranked as T-ZnO, n-ZnO and p-ZnO. The morphology had more obvious effect on H2O2 production than those of particle size and/or specific surface area. These results of H2O2 production was in accordance with the antibacterial activity correspondingly, which approved that H2O2 was the main active species resulting in high antibacterial activity of ZnO susensions. On this basis, the generating mechanism of H2O2 has been suggested, which is based on the dangling bond resulting from the nano-structure of ZnO as well as the active-center transformation of the adsorbed intermediate.The ZnOs were doped with Cu2+to examine the effect of modification on the efficiency of antibacterial activity. The results showed that Cu2+could be loaded into the hexahedral lattice of ZnOs through a solid-solution process, and the absorption bands for the as-doped ZnOs spread to visible region. Both the antibacterial activity and the H2O2 production in the Cu2+ doped ZnOs decreased, but the antibacterial activity tended to be increase with the increasing of doping concentration of Cu2+while the H2O2 production tended to be decrease with the increasing of doping concentration of Cu2+. It is thought that, based on the suggested mechanism of H2O2 generating, the Cu2+doping leads to lessen the dangling bond and to affect the O2 adsorption on the surface of ZnO, and on the other hand, the doped Cu2+may become the recombination center for the light excited electron-hole pairs, resulting in reducing the amount of H2O2. In addition, the doped Cu2+also brought into play antibacterial activity, so it got a raising effect with the increasing of the loading amount of Cu2+.