Functional Ag-TiO2 Thin Films on Porcelain: Oxalate-Assisted Sol-Gel Spray Coating for Antibacterial and Photocatalytic Applications

Thin films of TiO₂ and Ag-doped TiO₂ were successfully fabricated on commercial white-glazed porcelain bowls via a low-temperature oxalate-assisted sol–gel spray coating method using a water-based titanium oxalate precursor. X-ray diffraction confirmed the formation of highly crystalline anatase TiO₂ without secondary phases, even after doping with 10 wt% Ag. The nanostructured films exhibited uniform morphology with grain sizes of 15–20 nm and an average thickness of approximately 450 nm. Under visible-light irradiation (λ > 420 nm, 38,000 lux) from a 35 W xenon lamp, the Ag–TiO₂ thin films demonstrated enhanced photocatalytic activity, achieving 93.4% methylene blue degradation within 100 minutes. Antibacterial tests showed nearly complete inactivation of both Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) within 30 minutes of illumination. In addition, the coating significantly improved the surface hardness of the porcelain substrate (from Mohs 6–7 to 8–9). The coated surfaces maintained high gloss and aesthetic compatibility. These results indicate that Ag–TiO₂ thin films are highly effective for multifunctional ceramic products with antimicrobial, self-cleaning, and mechanical enhancement capabilities.