Photocatalytic and antibacterial properties of TiO2 and visible-light responsive Ag-TiO2 photocalysts embedded in polymer films

Purification of polluted water and air is a major issue nowadays and calls for urgent solutions globally. Hence, it is important to find well working, and energy efficient alternatives besides or instead of the regular air and water treatment technologies to remove harmful chemical compounds and pathogens, mold etc. from our environment by using the natural alternative energy sources such as sunlight. Visible-light responsive Ag-TiO2 was prepared by reduction of AgNO3 on the surface of TiO2 (wt%Ag = 0.5%). The formed Ag nanoparticles (NPs) had a particle size of 5-15 nm and showed strong Vis-light absorbance in the 400 – 500 nm wavelength range of the UV-Vis spectrum with a maximum at 455 nm. Light absorption of TiO2 is limited to the UV region (≤ 400 nm) because of its narrow band gap (Eg = 3.2 eV for anatase and 3.0 eV for rutile) which is not efficient considering to rely on solar energy solely to trigger the photocatalytic mechanism. Plasmonic noble metal NPs such as silver or gold, deposited in a small amount on TiO2 extends the light absorption of TiO2 into the Vis range. Moreover, they promote the electron-hole separation of the photocatalyst by acting as electron traps therefore significantly can increase the photocatalytic activity of TiO2 under UV or Vis light. Ag-TiO2 photocatalyst and TiO2 were embedded in [poly(ethyl acrylateco-methyl methacrylate; p(EA-co-MMA)] co-polymer to attain mechanically stable, photocatalytically active nanocomposite films. Ethanol was chosen as a model compound of VOCs and the degradation of ethanol vapour was followed on the composite films under UV-Vis light irradiation in a closed flat film reactor covered with quartz glass on the top to transmit the whole range of light emitted from the light source (Lighttech, Hungary, λ ≤ 254 nm, λmax=435 nm). The concentration of ethanol and intermediate products were monitored by GC-FID and -TCD. Antibacterial activity of the composite films was demonstrated by microbial tests using Methicillin resistant Staphylococcus aureus bacterium strain. Embedding of the photcatalyst into the polymer matrix necessarily decreased the photocatalytic activity by covering the surface of the NPs and blocking the active sites, but UV-treatment of the polymer films before the photocatalytic tests notably improved the photocatalytic activity by partially breaking the continuity of the polymer matrix. AFM, FTIR studies and contract angle measurements proved evidence of the chemical and structural transformation of the polymer film.