From the fluorescent lamp-induced bactericidal performance of sputtered Ag/TiO₂ films to re-explore the photocatalytic mechanism

Ag/TiO₂ composite films with the different Ag contents of 1, 3, and 5 vol.% were deposited at 25, 200, and 400 °C on glass substrates by radio frequency sputtering with a single cermet target formed by hot pressing the Ag nanoparticle-decorated TiO₂ nanopowder at 900 °C in argon atmosphere for 30 min, followed by annealing in air and the reduction under vacuum heating or by NaBH₄. All the TiO₂ films were analyzed by X-ray diffraction technique to have an amorphous structure. High deposition and annealing temperatures all led to Ag aggregation in Ag/TiO₂. Photodegradation of acid black 1 dye was used as the screen test to evaluate the photocatalytic ability of Ag/TiO₂ films, before the antibacterial test was preceded. The antibacterial ability on Escherichia coli was also evaluated. The 25 °C-deposited 3% Ag/TiO₂ films of 80 nm in thickness had the best performance in optical transmittance above 70% and killing the E. coli. The mechanism for the fluorescent lamp-induced bactericide of the 3% Ag/TiO₂ film is proposed. The amorphous 3% Ag/TiO₂ film had larger band gap of 3.67 eV than the annealed ones and is expected not to be excited by the fluorescent lamp, but to prolong the lifetime of the thermally induced, not photo-induced, charge carriers in the Ag/TiO₂ by its electric field of the illumination light and the attraction by Ag nanoparticles <8 nm in size. The Ag⁺ release mechanism for bactericide is not the major one here after comparing with the tests in the dark.