Role of cellulose, phenolic compounds, and water-soluble proteins in ZnO nanoparticle synthesis using Mangifera indica leaf extract for photocatalytic and antioxidant investigations

The green synthesis of zinc oxide nanoparticles (ZnO NPs) using plant-derived macromolecules offers an eco-friendly and sustainable approach to nanomaterial fabrication. In this study, Mangifera indica (MI) leaf extract, rich in cellulose, phenolics (mangiferin, quercetin), and water-soluble proteins, was employed as a natural reducing, capping, and stabilizing agent for the synthesis of ZnO NPs. The resulting NPs exhibited a hexagonal prism morphology, wurtzite crystal structure, and an average crystallite size of 61.5 nm. Zeta potential measurements confirmed excellent colloidal stability with a well-defined isoelectric point at pH 9.51, ensuring robust dispersion behavior. BET surface area analysis revealed a high specific surface area (125 m²/g) and mesoporous architecture, favoring enhanced adsorption and catalytic efficiency. UV-Vis spectroscopy indicated a narrowed bandgap of 2.9 eV, attributed to defect states and biomolecule interactions, facilitating improved light-harvesting ability. The photocatalytic performance of ZnO NPs was evaluated via Rhodamine B dye degradation, achieving 94 % degradation within 120 minutes under UV irradiation, following pseudo-first-order kinetics (k = 0.0275 min⁻¹). The mechanism, assessed through reactive species scavenging, identified hydroxyl (•OH) and superoxide (•O₂⁻) radicals as dominant oxidative agents. Additionally, ZnO NPs exhibited strong antioxidant activity, with 87.5 % DPPH radical scavenging efficiency at 12 mg/L and a total antioxidant capacity (IC₅₀ = 11.7 mg/L). These results highlight the synergistic role of bioactive macromolecules in tailoring the surface chemistry, dispersion stability, and functional performance of ZnO NPs, making them promising candidates for environmental remediation and biomedical applications.