An evaluation of some commercially-available thin TiO2 films and TiO2 films grown by atomic layer deposition for potential photocatalytic applications

Abstract

Atomic Layer Deposition (ALD) was utilized to synthesize nominally undoped titanium dioxide (TiO2) and a range of doped TiO2 films (Ti1-xO2:Mx) on quartz substrates, separately accommodating aluminium, gallium, hafnium, silver, tin and vanadium as nanolaminate dopants. The synthesized TiO2 and Ti1-xO2:Mx films provided varying photocatalytic activities dependent on differing degrees of crystalline morphology, Ti3+ concentrations and dopant used. Nominally undoped TiO2 was mainly amorphous, showing only minimal evidence of polycrystalline anatase structures and contained around 20 % Ti3+, providing a time to bleach (ttb) of 11 minutes 4 seconds ±35 seconds with respect to basic blue ink. In comparison to the nominally undoped TiO2 film, only the Ti1-xO2:Agx (19:1) and Ti1- xO2:Snx (19:1) films provided any photocatalytic improvement, recording basic blue 66 ink ttb values of 6 minutes 4 seconds and 5 minutes 12 seconds ±1 minute 13 seconds, respectively. This near halving of the ttb previously observed for the nominally undoped TiO2 film, probably originated from higher bulk Ti3+ concentrations (52 and 31 %) for the Ti1-xO2:Agx and Ti1-xO2:Snx films, respectively. Additionally, a novel approach was utilized, through which the effect of Irish hospital cleaning agents (Actichlor PlusTM, ChloraPrepTM, SteriCleanTM, and Virusolve+TM) on the photocatalytic activity of both the commercially available Pilkington ActivTM and ALDgrown Ti1-xO2:Snx films was examined. On different cleaning agent treatment, the photocatalytic activity of both films was found to decrease in respect to basic blue 66 and resazurin ink photodegradation, as well as increasing water contact angle hydrophobicity under UV light irradiation. However, the permanent damage to photocatalytic activity decrease was not incremental after multiple treatments for the non-residue creating cleaning agents (SteriCleanTM and Virusolve+TM) and cleaning agent treatment was shown to not mechanically degrade film morphology. Furthermore, both the Pilkington ActivTM and Ti1-xO2:Snx films showed inconclusive results for microbiological exposure with a complex interplay between E.coli colony attachment and photocatalytic destruction detected.