Atomic layer deposited TiO₂ films in photodegradation of aqueous salicylic acid

Degradation of salicylic acid (SA) with thin film photocatalyst, titanium dioxide (TiO₂), combined with ultraviolet (UV) radiation was studied. Photocatalysts were prepared on glass or silica substrate by atomic layer deposition (ALD) technique. The impact of initial SA concentration (10 and 75 mg/l) and pH (3-10) was studied. Reactions were faster on higher initial SA concentrations and decomposition of SA was greatest at pH 8. Varying deposition temperature and film thickness during ALD process influenced the efficiency of TiO₂. Crystallinity of the film changed with rising deposition temperature (150-450 °C) from amorphous to anatase and further to anatase rutile mixture, where rutile was the dominating phase. SA decomposition rate was greatest with catalysts consisting of both phases whereas pure anatase showed somewhat lesser efficiency and amorphous film did not work at all. Increasing film thickness enhanced the degradation of SA until the film was thick enough. With over 46 nm thick films the results remained the same. Two substrates, glass and silicon, were compared but the material was not found to have any evident impact on the catalytic efficiency of the film.