Photocatalytic Activity of Silver-Enhanced Crystalline Titanium Oxide Coatings

Objectives: The objective of this study was to determine if the incorporation of silver into anodized TiO₂ coatings would enhance photocatalytic activation (PCA) and antimicrobial properties.
Methods: 12.7 mm diameter commercially pure titanium grade 4 bar stock was cut into 2 mm thick discs. Specimens were anodized in a mixed-acid electrolyte containing 3.5 M sulfuric acid, 0.19 M phosphoric acid, 0.25 M oxalic acid, and 0.75 M hydrogen peroxide that was doped with either 0.05 M silver nitrate or 0.05 M silver acetate to final forming voltages of 144 V. Controls were anodized in the same mixed-acid electrolyte without the silver compounds. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were utilized to examine the oxide crystallinity, surface morphology, and surface chemistry. PCA was determined using a methylene blue (MB) degradation assay (n=6) using 365 nm UVA illumination over a four-hour duration. Antimicrobial properties were determined by assessing S. aureus attachment (n=3) with and without a one-hour of UVA illumination.
Results: XRD confirmed anatase phase in each anodized layer. SEM showed all specimens exhibited nano- and microscale surface porosity. EDS revealed silver was incorporated into the anodized layers in both silver-doped electrolytes. The silver acetate (p = 0.005) and silver nitrate (p = 0.003) doped anodized layers showed significantly higher MB degradation compared to controls. Increased PCA for silver-doped specimens continued to four hours (p < 0.001). T-tests revealed no significant differences in S. aureus attachment between the UVA illuminated and dark surfaces for each specimen type.
Conclusions: Incorporation of silver into the anatase TiO₂ layer showed enhanced PCA via MB degradation testing. However, no significant differences were shown in S. aureus attachment between silver-doped and control specimens in the light or dark. Future studies are warranted to assess silver-enhanced oxides against other strains of commonly acquired bacteria.