In this study, ceramic CaCu₃Ti₄O₁₂ (CCTO) and CaCu_3−xMg_xTi₄O₁₂ solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg²⁺ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu_3−xMg_xTi₄O₁₂ (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell–Wagner type relaxation, which is dependent on the temperature.

The ultrasonic treatment (UST) influence on properties of the ZnO-CeO₂ system (atomic ratios Zn/Ce = 25:75, 50:50, and 75:25) is studied. A decrease of the size of particles of the oxides, the formation of Zn-Ce-O nanocompositions, and an increase in the specific surface area of the samples are established. It is shown that the sonochemical treatment of oxide zinc-cerium mixtures allows one to increase their photocatalytic activity in the safranin T degradation process. A blue shift of the edge absorption in powder-like samples and an increase in the band gap energy (Eg) are fixed by the UV-vis spectroscopy. The catalytic test of the sonochemically treated ZnO-CeO₂ = 50:50 catalyst in the reaction of ethanol selective oxidation shows a possibility of its use in two processes: i) production of acetaldehyde with high selectivity in a low-temperature reaction (235 °C) with the recycle of the raw material, ethanol, and ii) hydrogen production without CO formation at temperatures more than 300 °C.

This study explores the sustainable synthesis of zinc oxide (ZnO) from industrial waste and its application in removing water contaminants such as chloramphenicol (CAP), metronidazole (MNZ), and prometryn (PROM). ZnO synthesized from zinc production waste (ZnO(2)) exhibited competitive photocatalytic performance compared to commercial ZnO (ZnO(1)), achieving 79% CAP degradation (Kd = 0.53 × 10⁻² min⁻¹) and 72% MNZ degradation (Kd = 0.43 × 10⁻² min⁻¹) under UV light, while showing higher activity in PROM degradation (32% removal) due to its mesoporous structure. Although ZnO(2) had a slightly lower specific surface area (24.9 m²/g) and pore volume (0.26 cm³/g) than ZnO(1), it demonstrated significant environmental and economic benefits by repurposing industrial waste. Catalytic tests in ethanol oxidation revealed ZnO(2) required higher temperatures for full conversion but exhibited higher acetaldehyde selectivity (70%). These findings highlight the potential of waste-derived ZnO as a sustainable alternative for water treatment and catalytic processes, aligning with circular economy principles and reducing reliance on natural resources.