Titania and silver–titania composite films on glass—potent antimicrobial coatings

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Abstract
Titania (anatase) and Ag-doped titania (anatase) coatings were prepared on glass microscope slides by a sol–gel dip-coating method. The resultant coatings were characterised by X-ray diffraction, X-ray absorption near edge structure (XANES), Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX) analysis, X-ray photoelectron spectroscopy (XPS) and UV-vis techniques and shown to consist of anatase with ca. 0.2–1 atom% Ag2O. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid, monitored by FT-IR spectroscopy. Photocatalytically-active coatings were screened for their antibacterial efficacy against Staphylococcus aureus (NCTC 6571), Escherichia coli (NCTC 10418) and Bacillus cereus (CH70-2). Ag-doped titania coatings were found to be significantly more photocatalytically and antimicrobially active than a titania coating. No antimicrobial activity was observed in the dark—indicating that silver ion diffusion was not the mechanism for antimicrobial action. The mode of action was explained in terms of a charge separation model. The coatings also demonstrated significantly higher activity against the Gram-positive organisms than against the Gram-negative. The Ag2O–TiO2 coating is a potentially useful coating for hard surfaces in a hospital environment due to its robustness, stability to cleaning and reuse, and its excellent antimicrobial response.