Photoreactive Anatase Consolidation Characterized by FTIR Spectroscopy

Titania (anatase) thin films were consolidated and hardened via UV irradiation when acidic precursor sols were diluted with 1-, 2-, and 3-carbon aliphatic alcohols. Titania sols were adjusted to pH values of 1.4, 2.3, or 3.1 and subsequently diluted with various mole fractions (X_ROH) of alcohol prior to film deposition. Re-esterification of the titania film surface was confirmed by transmission FTIR (Fourier transform infrared) spectroscopic characterization. In the dark (absence of UV), proton-catalyzed oxidation of the alkoxide functional groups produced a unique monodentate formic acid ligand. This further oxidized to bidentate bicarbonate and carbonate complexes. Given an equivalent fluence of UV light (20 J cm^-2, 254 nm), films became harder with increased proton concentration and X_ROH. UV light promoted formic acid and carbonate/bicarbonate removal by photocatalytic oxidation. The rate of loss of formic acid/bicarbonate species following UV irradiation increased with increasing proton concentration. With respect to carbon chain length, film hardness was found to follow MeOH > EtOH > ⁿPrOH for pH 1.4 and X_ROH = 0.48.