This research provides valuable insights into the application of ZnO nanoparticles in photocatalytic wastewater treatment. Process optimization was carried out by determining the ratio of the surface area to the energy band gap (S/E) in the photocatalysis rate under different sources of light (UV light, visible light, sunlight). The nanoparticles were synthesized using the precipitation technique, and the calcination process was carried out within a temperature range of 400 to 700 °C. The structural, morphological, and optical properties of materials were investigated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance (UV-Vis DRS), Raman spectroscopies, and Fourier transform infrared (FTIR) spectroscopies. The study demonstrates that calcination temperature significantly influences the photocatalytic activity of ZnO nanoparticles by altering their size, surface properties, shape, and optical behavior. Optimal decomposition efficiencies of Rhodamine B were achieved at 400 °C, with yields of 24%, 92%, and 91% under visible, UV, and sunlight irradiation, respectively. Additionally, the surface area decreased from 12.556 to 8.445 m²/g, the band gap narrowed slightly from 3.153 to 3.125 eV, and crystal growth increased from 0.223 to 0.506 µm as the calcination temperature rose. The photocatalytic properties of ZnO nanoparticles were assessed to determine their efficiency in decomposing Rhodamine B dye under operational parameters, including pollutant concentration (C0), sample amount, pH level, and reaction time. The sample exhibited the best breakdown rates with C0 = 5 mg/L, solid-to-liquid ratio (S/L) = 50 mg/L, pH = 7, and reaction time = 1 h. Additionally, we combined two oxidation processes, namely H₂O₂ and photocatalytic oxidation processes, which significantly improved the Rhodamine B removal efficiency, where 100% of RhB was degraded after 60 min and 100 µL of H₂O₂.

This work presents microstructure and mechanical properties of NiWCrBSi coatings produced onto mild steel substrate by oxyacetylene flame spraying, using two different stoichiometries. Coatings were analysed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. Microhardness tests were carried out using a micro-hardness tester operating with Vickers indenter and the load being 3N. Results showed that both coating microstructures were of lamellar/stratified type, containing several inhomogeneities such as unmelted particles and pores. Coatings consisted mainly of a solid solution (Ni, Cr and Fe), containing two different phases of hexagonal structure, namely WC and Ni₃₁Si₁₂. The presence of WC hard particles contributed to the high coating hardness. Oxidizing flame conditions showed a potential interest for tribological applications, because of a reduced porosity and an increased coating hardness.

ZnO–ZnCr₂O₄ heterojunction nanocomposites were synthesized via co-precipitation with nominal spinel loadings of 10, 20, and 30 wt.% (denoted ZnCr-10, ZnCr-20, ZnCr-30) to evaluate structure–property–performance relationships in photocatalytic dye degradation. Rietveld refinement of XRD data revealed actual crystalline phase fractions of 12.1%, 32.4%, and 39.9% ZnCr₂O₄, respectively, with systematic morphological evolution from dispersed nanoparticles (ZnCr-10) to densely agglomerated structures (ZnCr-30) observed by SEM. Optical analysis demonstrated that ZnCr-10 (apparent band gap 3.09 eV) retains ZnO-dominated absorption with moderate interfacial electronic coupling, while ZnCr-20 shows enhanced visible response (2.89 eV) through interface-mediated transitions. ZnCr-30 exhibits strong sub-bandgap absorption (1.63 eV) originating from defect states rather than intrinsic band narrowing. Photoluminescence studies under UV excitation revealed optimal radiative recombination suppression in ZnCr-10, consistent with efficient interfacial charge separation, whereas excessive loading (ZnCr-30) introduced defect-mediated recombination centers. Photocatalytic degradation of Rhodamine B (5 mg/L, 0.5 g/L catalyst, solar irradiation) followed the order: ZnCr-10 (k = 0.0307 min⁻¹) > ZnO (0.0203 min⁻¹) > ZnCr-20 (0.0230 min⁻¹) > ZnCr₂O₄ (0.0166 min⁻¹) > ZnCr-30 (0.0113 min⁻¹). The optimal ZnCr-10 performance is attributed to balanced interfacial contact between phases enabling charge separation without excessive agglomeration or defect accumulation. Operational parameters (pH 7, 50 mg/100 mL, 100 µL H₂O₂) were optimized, achieving 98% degradation in 60 min. This study demonstrates that photocatalytic enhancement in ZnO–spinel heterojunctions is governed by interfacial architecture and defect management rather than optical absorption alone, providing design principles for efficient solar-driven environmental remediation.