Characterization of Pd-modified TiO2-based thin films and their effect on photocatalytic activity

Thin film technology has made significant contributions to the field of photocatalysis through improvements in surface properties and a decrease in material costs. Therefore, the present study aims to evidence the properties that Pd can confer to TiO₂ thin films prepared by chemical vapor deposition technique and to verify their effectiveness as photocatalysts in the degradation reaction of the carbinol-based malachite green dye. TiO₂ films with different nominal Pd contents (2.8, 3.7, 4.6, and 6.4 at. % Pd) synthesized by CVD at 400 °C and 1 Torr pressure exhibit significant changes in their crystal structure, morphology, and electronic properties. On the one hand, at low concentrations (2.8 and 3.7 at. % Pd), substitutional doping is promoted. In contrast, the increase in concentration (4.6 and 6.4 at. % Pd) encourages the formation of PdO and PdTiO₃ phases, as indicated by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy results. The anatase phase is partially inhibited by other phases, such as Pd–O and Ti-Pd–O; consequently, the grain size that constitutes the film is considerably reduced, and microstrains are increased. On the other hand, the study of the optical properties reveals a decrease in the bandgap energy and the recombination velocity of the charge carriers, resulting in a maximum degradation of 67% of the dye, which is obtained with film 4.6 at. % Pd, attributed to a synergistic effect between the observed properties.