Dual-Functional Zinc Oxide Nanoparticles@polydopamine and Loaded Cellulose Nanofibers for Synergistic Photodegradation of Malachite Green and Antibacterial Performance in Water Remediation

The extensive discharge of harmful dyes such as malachite green (MG) into aquatic environments poses significant ecological and health challenges resulting from its toxic effects, durability, and resistance to traditional treatment approaches. Therefore, the current investigation presents the fabrication and evaluation of a novel dual-functional zinc oxide nanoparticles (ZnONPs) coated with polydopamine (PDA) and embedded into cellulose nanofibers (CNF) (ZnONPs@PDA-CNF), designed for synergistic photocatalytic degradation of MG dye and antibacterial performance in wastewater treatment. The prepared material was synthesized via a green, scalable approach and then characterized using SEM–EDX, XPS, BET and pore size distribution. Results of the photocatalytic tests under visible light revealed that ZnONPs@PDA-CNF achieved complete MG degradation (100%) within 90 min under optimal conditions. The improved potential activity was attributed to the extended visible-light absorption enabled by the π-conjugated structure and donor–acceptor characteristics of PDA, which facilitate enhanced electron excitation and transfer. Further, the scavenger studies identified hydroxyl radicals as the dominant reactive species, supported by the proposed photocatalytic mechanism. Moreover, the antibacterial assays of prepared material demonstrated the strong growth inhibition against some pathogenic bacteria, with ZnONPs@PDA-CNF outperforming ciprofloxacin. Furthermore, the ecotoxicity evaluation confirmed the treated effluent's safety and biocompatibility. Likewise, the prepared material exhibited excellent reusability, retaining 84.6% activity after five cycles, and demonstrated economic feasibility with low operational costs and alignment with circular economy principles. Overall, the present investigation revealed that, the ZnONPs@PDA-CNF represents a sustainable and highly efficient material for simultaneous pollutant degradation such as toxic dyes and disinfection of pathogenic bacteria, offering significant potential in eco-friendly wastewater treatment technologies.