Investigation of Reaction Dynamics and Mechanistic Pathways in the Remediation of Dye-Contaminated Wastewater Using Biogenic Nanostructured Dc-ZnO.

Abstract

Dye contamination in wastewater, exacerbated by industrial activities significantly impacts aquatic ecosystems, rendering water unsuitable for potable use and impairing agricultural productivity. This study reports the eco-friendly synthesis of zinc oxide (ZnO) nanoparticles using Dryopteris cristata (L.) leaf extract (Dc-ZnO), with the potential to degrade dye pollutants. The physicochemical properties of the synthesized nanoparticles were meticulously characterized using analytical techniques including PL, UV-vis., XRD, SEM-EDX, TEM-SAED, TGA, and FT-IR. The Dc-ZnO nanoparticles exhibited high photocatalytic activity for the degradation of cationic (methylene blue, MB) and anionic (congo red, CR) dye under visible light irradiation in the presence of H₂O₂ as a green oxidant. Optimization of experimental parameters, including pH, catalyst loading, light exposure, and H₂O₂ concentration, resulted in photodegradation efficiencies of 94.32% for MB and 96.16% for CR within 60 min. Kinetics studies indicated pseudo-first-order reaction behavior, with rate constants of 4.9 × 10^-2 min^-1 for CR and 6.3 × 10^-2 min^-1 for MB. The quantum yields for MB and CR were calculated to be 5.77 × 10^-9 and 6.27 × 10^-9 molecules photon^-1, respectively. Radical scavenging studies confirmed hydroxyl radicals (•OH) as key intermediates. The catalyst maintained high stability over five cycles, demonstrating its potential for sustainable wastewater treatment.