Evaluation of the antibacterial activity of Co-based Zeolitic Imidazolate Frameworks and validation in a daily environment

Abstract

This study investigates the antibacterial potential of cobalt-based zeolitic imidazolate frameworks (ZIFs)—specifically, ZIF-67, ZIF-L-Co, and ZIF-9—for antimicrobial coatings on high-contact surfaces. Synthesized via solvothermal methods, ZIFs containing 2-methyl-imidazole (2MIm) and benzimidazole (PhIm) ligands exhibited varied bactericidal efficacy based on ligand structure and cobalt ion availability. Chemical analyses confirmed distinct morphologies and surface properties, with open cobalt sites in ZIF-67 and ZIF-9 and elongated structures in ZIF-L-Co. FTIR and XRD analyses verified the unique ligand compositions and sodalite-type crystalline structure of ZIF-9 and ZIF-67, with morphological differences in SEM images linked to ligand size. Among the tested materials, ZIF-67 demonstrated the highest antibacterial activity due to its extensive surface area (1128 m²/g) and enhanced generation of reactive oxygen species (ROS), achieving >70 % inhibition of E. coli at 62.5 µg/mL within 3–24 hours. Comparatively, ZIF-9 exhibited 99 % inhibition against S. aureus and E. coli at 125 µg/mL, while ZIF-L-Co required 250 µg/mL to maintain similar inhibition levels over 24 hours against E. coli. Environmental validation on ZIF-67 as a door handle coating shows no microbial growth after 5 days of continuous use, demonstrating the higher bactericidal capacity of ZIFs nanostructures under real conditions, with potential application as effective antibacterial coatings. These findings highlight the critical influence of cobalt ion availability and ligand structure on bactericidal efficiency, underscoring ZIF-67’s potential for durable antimicrobial applications in frequently used environments.