In this study, pure ZnO and Ho-doped ZnO powders (1 and 2 mol % Ho) were synthesized via hydrothermal and sol–gel methods and evaluated for their tribocatalytic activity toward the degradation of paracetamol, an emerging pharmaceutical contaminant in aquatic environments. Structural, morphological, and optical properties of the obtained materials were investigated by X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. SEM observations revealed pronounced morphology differences between the synthesis routes, with hydrothermally prepared samples exhibiting well-defined rod-like structures. XPS and EPR analyses provided evidence for successful Ho modification of ZnO and the presence of defect-related electronic states associated with Ho doping. The tribocatalytic performance was examined in distilled, tap, and mineral water using friction rods with different geometries in order to assess the influence of synthesis route, Ho concentration, and water composition. Among all the investigated materials, hydrothermally synthesized ZnO doped with 2 mol % Ho exhibited the highest tribocatalytic activity, achieving 96.91% degradation of paracetamol at an initial concentration of 15 mg/L within 24 h. The enhanced performance was attributed to improved charge separation induced by Ho modification, combined with the favorable rod-like morphology of the particles. Higher degradation efficiencies were observed in distilled water compared to tap and mineral water, indicating the important role of dissolved ions during the tribocatalytic process. These findings demonstrate that the synthesis route, Ho doping, and water composition collectively govern the tribocatalytic performance of ZnO-based materials, highlighting their potential for water purification.

Tribocatalysis is an emerging approach for the oxidation of organic pollutants using frictional energy. ZnO nanorods were prepared by thermal decomposition of zinc acetate dihydrate and wet-chemically modified with Gd₂O₃, Dy₂O₃, or Er₂O₃. SEM, nitrogen sorption, XRD, ATR-FTIR, Raman spectroscopy, and XPS confirmed the formation of predominantly rod-like ZnO, preservation of its morphology and wurtzite structure after modification, and introduction of nanocrystalline RE₂O₃ phases. Tribocatalytic activity was evaluated under mechanical stirring using the anionic dye Reactive Black 5 (RB5) and the cationic dye Brilliant Green (BG), examining the effects of RE modification, stirring rate, friction pair, scavengers, and catalyst reuse. Removal increased with stirring rate and was consistently higher for RB5. At 800 rpm, Er:ZnO exhibited the highest activity toward both dyes, reaching approximately 81% RB5 removal (k_app ≈ 0.074 h⁻¹) and 56% BG removal (k_app ≈ 0.040 h⁻¹) after 24 h. COD removal reached 53–60% for RB5 and 27–43% for BG, indicating a reduction in the oxidizable organic load consistent with partial mineralization. ATR-FTIR revealed carbonate formation and PTFE transfer to recovered catalysts, highlighting surface changes and secondary contamination. The results demonstrate measurable tribocatalytic activity and show that the benefits of RE modification depend on the target dye.