AAO-ZnO nanocomposite coatings on aluminum alloy surface with high bonding strength and long-lasting antibacterial properties

Abstract

A robust and durable antibacterial nanocomposite coating consisting of anodic aluminum oxide (AAO) and zinc oxide (ZnO) was synthesized by sol–gel deposition of ZnO onto AAO nanotubes. This unique coating features a dual-layer structure: an intermediate AAO + ZnO layer (∼3.9 μm) and a ZnO layer (∼0.8 μm). Nanosized ZnO particles, ranging from 20 to 40 nm, nucleate and grow along the walls of AAO nanotubes within this structure. AAO nanotubes, functioning as “nanocontainers”, offer appropriate sites for the deposition of ZnO particles. The mechanically interlocked AAO + ZnO interlayer enhances the adhesion between the external layer and the inner substrate. Meanwhile, this interlayer facilitates the sustained release of both Zn2+ ions and reactive oxygen species (ROS), effectively impeding bacterial proliferation. Ultraviolet antibacterial tests reveal that the AAO + ZnO interlayer maintains exceptional antibacterial efficacy, even after removing the outermost ZnO layer. The antibacterial rates of the AAO + ZnO interlayer against the above two typical bacteria (E. coli and S. aureus) after 1 h could still reach 91.4 % and 89.0 %, respectively. Specifically, AAO nanopores serve as an inert container for ZnO nanoparticles with consistently release of Zn2+ ions and reactive oxygen species (ROS), thereby ensuring the long-term antibacterial effectiveness of the AAO-ZnO coating. This research also demonstrates the significant potential of AAO-ZnO nanocomposite coating on aluminum alloys for durable antibacterial applications.