This study addresses the growing environmental challenge posed by dyes, which are highly persistent and toxic contaminants that require advanced and sustainable treatment technologies. Zinc oxide nanoparticles (ZnO NPs) were synthesized through a green processing route using Rosa gallica extract as a reducing and stabilizing agent. By varying the extract concentration (2–8% w / v ), the synthesis conditions were optimized, enabling the establishment of clear processing-structure-property relationships. XRD confirmed the formation of the hexagonal wurtzite phase, while FTIR, SEM, TEM, UV–Vis, and photoluminescence analyses demonstrated that increasing the extract concentration led to smaller nanoparticle sizes (from 26 to 11 nm), improved size uniformity, and noticeable modifications in optical behavior consistent with quantum confinement effects. The photocatalytic performance of the synthesized ZnO NPs was evaluated against six model dyes, including azo and cationic dyes. The results demonstrated that both extract concentration and the dye molecular structure strongly influence degradation efficiency. Among the samples, ZnO/RC8 exhibited the highest photocatalytic activity, achieving degradation efficiencies of 78–99% for azo dyes and 93–96% for cationic dyes under UV irradiation. These findings highlight the potential of green-synthesized ZnO nanomaterials as functional photocatalysts with tunable properties for environmental applications. • Green synthesis enabled tunable structure-property control in ZnO nanoparticles. • Rosa gallica extract modulated ZnO crystallite size, defects, and optical behavior. • Structure-property variations dictated degradation of azo and cationic dyes. • ZnO/RC8 from the highest extract concentration delivered the best photocatalytic performance.
Robles et al. (Sun,) studied this question.