Photo-degradation enhancement on crystal violet under sunlight via synergistic effect of Cd2+ doped ZnTiO3 and its sulfide nanocomposite as ZnxCd1-xTiO3@S

This research delved into the efficacy of photocatalysis in ZnTiO₃ perovskite structures doped with Cd²⁺ ions and their corresponding sulfide nanocomposites when exposed to solar radiation. ZnTiO₃, Zn_xCd_1-xTiO₃ photocatalysts (x = 0.01, 0.03, 0.05), and Zn_xCd_1-xTiO₃@S nanocomposites with varying sulfur contents (5, 10, 20, and 30 %) were synthesized utilizing the hydrothermal method. X-ray analysis confirmed the crystal structures of the synthesized samples. A single-phase Zn_xCd_1-xTiO₃ with a cubic structure was achieved exclusively at the molar ratio x = 0.01 (Zn_0.99Cd_0.01TiO₃). Structural parameters, such as crystallite size (nm), lattice constants (Å), unit cell volume (Å)³, lattice strain (ɛ), and dislocation density (δ), were derived from XRD data. TEM micrographs revealed cubic morphology for Zn_0.99Cd_0.01TiO₃ and multishell hollow structures with hexagonal shells for the Zn_0.99Cd_0.01TiO₃@S nanocomposite. XPS spectra confirmed the oxidation states of Cd²⁺, S²⁻, and S⁶⁺ in the Zn_0.99Cd_0.01TiO₃@S nanocomposite. Band gap energies of the photocatalysts were estimated using DRS spectra and Tauc plots, showing a slight reduction, shifting from 3.27 eV down to 3.25 eV upon Cd²⁺ doping into ZnTiO₃, while sulfur addition led to a further reduction. Despite a decrease in band gap energy and a marginal increase in surface area, Cd²⁺ ion-doped ZnTiO₃ exhibited lower photocatalytic activity in degrading crystal violet compared to pure ZnTiO₃ (65.53 % vs. 75 %). Conversely, the Zn_0.99Cd_0.01TiO₃@S20 sulfide nanocomposite demonstrated superior performance, achieving 96.40 % degradation within the first 30 min. Scavenger studies identified h⁺ and e⁻ as the major reactive species, with ^•OH playing a minor role. Kinetic studies employing models of pseudo-zero order, pseudo-first order, and pseudo-second order were performed, underscoring the effectiveness of the Zn_0.99Cd_0.01TiO₃@S nanocomposites during the photodegradation activity.