Capped Co/ZnO nanocomposites: A comparative study of antibacterial activity with alumina, silica, and ceria

This study investigates the antibacterial activity of cobalt/zinc oxide (Co/ZnO) nanocomposite nanoparticles synthesized using the co-precipitation method. The nanoparticles were capped with alumina (Al₂O₃), silica (SiO₂), and cerium (CeO₂) at a 2 % concentration, and their antibacterial properties were evaluated against Escherichia coli and Staphylococcus aureus using the agar diffusion method. The results demonstrated that metal capping significantly enhances antibacterial efficacy, increasing inhibition zones at higher nanoparticle concentrations. Cerium-capped Co/ZnO exhibited the highest antibacterial activity among the capped nanoparticles. Structural characterization through X-ray diffraction (XRD) confirmed the nanoscale crystalline size, with crystallite sizes of 20.56 nm (Co-ZnO), 20.50 nm (Al₂O₃-capped), 22.21 nm (CeO₂-capped), and 21.62 nm (SiO₂-capped). The optical properties were analyzed by determining the energy band gaps, revealing values of 3.29 eV (Co-ZnO), 3.28 eV (CeO₂-capped), 3.26 eV (SiO₂-capped), and 3.25 eV (Al₂O₃-capped). The enhanced antibacterial properties of metal-capped Co/ZnO nanocomposites are attributed to additional surface functionalities introduced by the metal caps, which improve reactive oxygen species (ROS) production and bacterial interactions. These findings highlight the potential of metal-capped Co/ZnO nanocomposites as effective antimicrobial agents, paving the way for their applications in biomedicine and environmental safety.