From zinc oxide nanoparticles to microflowers: A study of growth kinetics and biocidal activity

Zinc oxide (ZnO) particles with varying morphologies from spherical particles to flower-like structure were synthesized by a simple wet-chemical method involving reaction between metal acetate and a long chain amine by an addition–elimination process. The influence of amine as a precursor and morphology directing agent is illustrated and the possible mechanism is discussed. Structural and optical studies reveal the formation of hexagonal wurtzite structure of ZnO with sufficient defects in the form of oxygen vacancies and the concentration of defects has been found to be dependent on the shape of zinc oxide nanostructures (ZnO-NSs). As example for promising applications, the antibacterial activities of the as prepared ZnO-NSs were preliminarily studied against gram positive (Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus agalactiae and Bacillus subtilis) and gram negative (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium) bacteria and are found to be dependent on the shape of the nanostructures. Survival percentage of each of these pathogens in the presence of the nanostructures has been evaluated. Antibacterial efficacies of the nanostructures were calculated and it has been observed that spherical nanoparticles are most toxic among the nanostructures tested. The major contribution for this biocidal activity has been proposed to arise from the release of reactive ion species (ROS) from the surface of ZnO when in solution.