Study of the water content on the CdO + CdTiO3 crystalline grains distribution in thin films obtained by sol-gel and their effect on the morphological, optical, and photocatalytic properties

Abstract

CdO+CdTiO3 multicomponent oxide thin films were obtained by mixing the CdO and TiO2 sol-gel precursor solutions, keeping Ti/Cd = 0.65. TiO2 solution water content was varied from 0 to 5 mol (X) for each Ti mol in steps of 1 mol to evaluate its effect on the properties of the CdO+CdTiO3 films. The films were obtained by the dip coating method under controlled temperature and relative humidity conditions. Superficial morphology images by optical and scanning electron microscopy revealed a strong effect of the water content on the CdO and CdTiO3 crystalline grains distribution, showing three different zones. This result was remarked from X-ray diffraction, EDS measurements, UV-Vis, and Raman spectroscopy. In addition, the photocatalytic activity of CdO+CdTiO3 films was evaluated from the methylene blue in water photobleaching. For the first time, a notable effect of the distribution and content of CdO and CdTiO3 crystalline grains on the photocatalytic activity of the films is reported. The best photocatalytic activity (k = 0.66 h−1) is obtained for the films deposited with X = 4 mol, corresponding to those with crystalline grains distribution most homogeneous. Also, for these films, the highest Cd excess content to Ti is found (30%), so the highest photocatalytic activity is explained by the higher amount of CdO and CdTiO3 crystalline grains coupled.