Development of nanostructured photocatalytic coatings for anti-bioadhesion and self-cleaning of residual bacterial cells

Abstract

In this work, nanostructured oxide coatings with photocatalytic activity were prepared by anodization, Zn acetate (ZnAc) modification and/or annealing, enabling high-performance anti-bioadhesion and self-cleaning of residual bacterial cells and biofilm upon sunlight irradiation and/or H2O2 treatment. The morphology, surface roughness, composition and semiconducting properties of the nano-coatings were characterized by atomic force microscopy, Raman spectroscopy and ultraviolet (UV)-visible diffuse reflectance spectroscopy. The anti-adhesion of the coatings to P. aeruginosa bacteria was measured by a confocal laser scanning microscope, and their electrochemical stability was evaluated by open-circuit potential and linear polarization resistance measurements in a chloride solution. The results demonstrate that, compared to the prepared anodized, annealed and 1-time ZnAc modified nano-coatings, the 2-time ZnAc modified nano-coating containing photocatalytic ZnFe2O4 achieves the best anti-bioadhesion performance and self-cleaning of residual bacterial cells and biofilm, while maintaining a high electrochemical stability. The nano-coating achieves 99.6% of anti-bioadhesion under sunlight irradiation relative to bare steel. The treatment of 1 h UV irradiation and 0.02 mM H2O2 allows 99.3% of removal of bacterial cells and biofilm plaques which are formed in the absence of sunlight. The high-performance anti-bioadhesion of the nano-coating is attributed to production of a high concentration of O2− induced by photocatalytic activity of the ZnFe2O4 component contained in the coating. Under combined UV irradiation and the addition of H2O2, the •OH is produced due to the photocatalytic reaction of H2O2 with O2− or photo-electrons on the coating. The periodic H2O2 treatment provides a promising strategy to re-store the nanostructure of the prepared coatings, and sustain their high performance for anti-bioadhesion.