In this work, nanocomposite materials of barium titanate in tetragonal syngony with 1% and 10% copper(II) oxide were prepared by the sol–gel synthesis method. The influence of CuO and its amount on the photocatalytic properties during the decomposition of rhodamine B in both air and water was investigated. It was found that with an increase in the amount of copper oxide the decomposition of the water dye solution increases under UV irradiation, while the opposite trend is observed in air. Studies on the photoactivity of nanocomposite materials under the action of visible light have shown that dye removal is better in air on a solid surface than in water. The results of the physico-chemical investigation methods, in particular XRD analysis, Raman spectroscopy, scanning electron microscopy, specific surface area and calorimetry, have revealed the structural features of the samples and described the presumed mechanism of photocatalytic activity.
