Antibacterial-Enhanced Benzoxazine-Functionalized ZnO Nanoparticles for Anticorrosion Sol–Gel Coatings

In this paper, benzoxazine-functionalized silane (BzPTES) was grafted onto zinc oxide nanoparticles (ZnO NPs) to afford antibacterial-enhanced and dispersible functionalized nanoparticles (ZnO-Bz), which were subsequently incorporated into a sol–gel coating system to construct a dual-functional composite coating with excellent corrosion resistance and antibacterial properties. The structure and dispersion of ZnO-Bz were characterized by FTIR, zeta potential, TGA, and elemental analysis. Coatings’ performance was evaluated by EIS, salt spray test, water contact angle, water absorption tests, plate counting method, and minimum inhibitory concentration (MIC). Results show that Bz functional groups were successfully grafted onto ZnO with a grafting ratio of approximately 2.59 wt %. After 30 days of immersion in 3.5 wt % NaCl, the coating with 1 wt % ZnO-Bz maintained a charge transfer resistance exceeding 10 GΩ·cm2, demonstrating the best corrosion resistance. Antibacterial tests showed that the MIC of ZnO-Bz against E. coli and S. aureus was 39 μg/mL, markedly lower than that of unmodified ZnO NPs (39 μg/mL and 156 μg/mL). All coatings containing ZnO-Bz achieved a 100% antibacterial rate against both strains, while the unmodified coating showed rates of only 64.08% and 75.09%, respectively. Incorporating an appropriate amount of ZnO-Bz via a matrix-compatible modification strategy provides an effective approach for developing multifunctional coatings combining corrosion resistance and antibacterial functions.