Controlling ZnO Nanoparticle Morphology and Photocatalytic Degradation of Methylene Blue through Solvothermal Parameters

The pursuit of highly efficient photocatalysts necessitates precise control over nanoparticle synthesis to tailor their physicochemical properties. While zinc oxide (ZnO) is a promising photocatalyst, the quantitative relationship between its synthesis conditions, resulting morphology, and photocatalytic efficiency remains inadequately mapped. This study presents a systematic investigation into the solvothermal synthesis of ZnO nanoparticles, explicitly varying three critical parameters: precursor concentration (0.05 M, 0.1 M, 0.2 M), reaction temperature (120°C, 150°C, 180°C), and solvent composition (100% Water, 50/50 Water/Ethanol, 100% Ethanol). We demonstrate that these parameters exert a profound and predictable influence on the resulting nanoparticle morphology, transitioning from nanospheres to nanorods and complex hierarchical structures. Comprehensive characterization (XRD, SEM, TEM, BET, UV-Vis/DRS) revealed that the sample synthesized at 0.1 M, 150°C, in a 50/50 Water/Ethanol medium (denoted Z-150-WE) exhibited an optimal balance of properties: a high aspect-ratio nanorod morphology, high crystallinity, a specific surface area of 45 m²/g, and a bandgap of 3.15 eV. This sample demonstrated superior photocatalytic performance, achieving 98.5% degradation of methylene blue (MB, 10 ppm) under UV irradiation in 60 minutes, significantly outperforming commercial ZnO (68% degradation). A direct correlation was established between the nanorod morphology, enhanced charge carrier separation, and photocatalytic activity. This work provides a definitive roadmap for the rational design of ZnO photocatalysts by establishing clear synthesis-property-performance relationships, paving the way for targeted nanomaterial development for environmental remediation.