Ultrasonic-assisted preparation of zinc oxide for bacteria inhibition: influence of dispersants and antibacterial mechanism

It is well known that zinc oxide (ZnO) is recognized as a highly effective and stable inorganic antibacterial material. The dispersibility and microstructure of ZnO play crucial roles in determining its antibacterial activity. In this investigation, we successfully synthesized ZnO nanoparticles with exceptional dispersibility and potent antibacterial properties through ultrasonic sonication, utilizing sodium hexametaphosphate, sodium dodecyl benzene sulfonate, and sodium polyacrylate as effective dispersants. To comprehensively assess the impact of these dispersants on the structure and morphology of the ZnO nanoparticles, various characterization techniques, including X-ray diffraction analysis, transmission electron microscopy imaging, Fourier transform infrared spectroscopy, thermogravimetric analysis, UV‒Vis absorption spectroscopy, X-ray photoelectron spectroscopy, and zeta potential analysis, were employed. The average particle sizes calculated for ZnO-SHMP, ZnO-SDBS, and ZnO-PAAS are approximately 300 nm. The zeta potential of ZnO-SHMP, ZnO-SDBS, and ZnO-PAAS are − 18.67, -12.77, and − 16.77 mV, which is significantly lower than that of the pristine ZnO (-2.01 mV). Our findings demonstrate that the addition of dispersants significantly enhances the dispersibility of ZnO nanoparticles while also improving their antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by achieving an antibacterial rate exceeding 99%. It’s observed that the introduction of dispersants led to morphological changes in the ZnO particles, contributing to their enhanced antibacterial activity. Compared with dark conditions, particularly under fluorescent lamp irradiation, superior antibacterial effects were achieved. Mechanistically, our findings suggest that the synergistic effect of the ZnO-bacteria interaction, along with soluble Zn²⁺ ions and the generation of reactive oxygen species, accounts for the observed antibacterial efficacy. The average contents of ZnO-PAAS released Zn²⁺ in the liquid culture media of E. coli and S. aureus were 27.5 mg/L and 41.1 mg/L, respectively, higher than that of the pristine ZnO. The incorporation of ZnO, which is prepared with a dispersant, into waterborne paint yields a pronounced antibacterial effect, rendering it highly promising for practical applications such as antibacterial coatings.