Green-Synthesized Ag/Zn Nanocomposites from Chlorella vulgaris Polar Extract: Sustainable Photocatalytic Water Remediation and Kinetic Modeling

The growing demand for sustainable water treatment technologies requires photocatalysts that combine low environmental impact, energy efficiency, and mechanistic robustness. In this work, A g / Z n nanocomposites were green-synthesized using Chlorella vulgaris polar extract as a bio-mediated reducing and stabilizing agent, eliminating hazardous reagents and high-energy processing steps. Structural characterization (XRD, FTIR, SEM, UV–Vis) confirmed the coexistence of crystalline wurtzite Z n O with metallic A g and A g 2 O phases. Photocatalytic activity was evaluated through Congo Red degradation under a sequential dark–light protocol, enabling clear separation of adsorption and photoactivated pathways. During the 60 m i n dark stage, removal remained limited ( ~ 9 – 11 % ), consistent with adsorption–desorption equilibration. Upon UV irradiation, a distinct kinetic transition occurred, leading to final removal efficiencies of 44 – 49 % after 180 m i n . Notably, performance remained stable across the investigated photon flux range, indicating operation beyond a strictly photon-limited regime and highlighting an intrinsically energy-resilient catalytic response. A mechanistic kinetic model integrating reversible adsorption with light-dependent degradation accurately reproduced all experimental profiles ( N R M S E = 3.14 % ) and successfully predicted an independent dark-control experiment without additional fitting. By coupling green synthesis with quantitative kinetic validation, this study proposes a sustainability-oriented framework for designing photocatalysts that align low-impact fabrication with energy-conscious water remediation.