Photocatalytic Properties of Quartz Glass with Titanium Oxide Coatings of Varying Thicknesses, Synthesized by Molecular Layer Deposition

The photocatalytic properties of titanium oxide (TiO2) coatings of various thicknesses synthesized by molecular layering (ML) method are studied on the surface of quartz glass plates, using photodegradation of Chicago Sky Blue 6B dye under UV-irradiation as a model reaction. The thickness and optical parameters of the coatings are determined by spectral ellipsometry, and the elemental composition is determined by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM/EDS); and the morphology and continuity of the coatings are analyzed by atomic force microscopy (AFM). It is found that when the thickness of the titanium oxide layer is ≥24 nm, a single-phase, continuous titanium dioxide film is formed, completely covering the surface of the quartz substrate. It is shown that the rate of photodegradation of the dye reaches a plateau after the substrate is completely covered by the titanium oxide layer and remains virtually unchanged with a further increase in thickness. The obtained thickness–activity dependences set the minimum required thickness of TiO2 to achieve maximum photocatalytic efficiency under the given conditions and demonstrate the effectiveness of the ellipsometry, SEM/EDS, and AFM for monitoring the structure and continuity of ML-grown coatings.