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

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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.