The development of stable, sunlight-mediated photocatalysts capable of simultaneously removing chemically diverse organic pollutants remains a critical challenge for sustainable wastewater remediation. This study report is an interfacial engineered and eco-friendly biogenic Ag/Cu–Zn trimetallic heterostructure stabilized by tannic acid for efficient degradation of a mixed cationic-anionic dye system (methylene blue and methyl orange). The synergistic interaction of heterostructures between plasmonic and non-plasmonic metals was optimized, which helps to optimize surface area and energy level modulation, and maximum photocatalytic enhancement was achieved. The nanoparticles were comprehensively characterized using UV–Vis diffuse reflectance (UV–Vis), powder X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), digital optical microscopy, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopic techniques. The analyses confirmed the successful synthesis of the small-sized trimetallic nanoparticles with spherical and quasi-spherical structures and a zerovalent state. This catalyst accomplishes remarkable simultaneous degradation of mixed dye, methylene blue (97.1%), and methyl orange (96.6%) under natural sunlight. The optimized Ag/Cu–Zn trimetallic heterostructure exhibited superior photocatalytic performance at a 15 mg catalyst load, pH 8, and 10 ppm mixed dye concentration within 60 min of sunlight irradiation. The integration of a plasmonic metal coupled with a non-plasmonic counterpart facilitates a strategic transfer of energetic hot electrons to the non-plasmonic band. This architecture not only enhances light harvesting across a broad spectral range but also suppresses charge carrier recombination and collectively accelerates the generation of reactive species, resulting in an enhanced photocatalytic reaction. Tannic acid also improved the stability and photocatalytic activity of Ag/Cu–Zn nanomaterials by preventing aggregation, maintaining surface accessibility and improve the photocatalytic activity. The effect of different scavengers was examined, and the results indicate that superoxide radicals (•O₂⁻) contribute substantially to the degradation of both dyes. The degradation rate of mixed dye using the nanoparticles followed pseudo-first-order kinetics and was greatly influenced by the studied parameters. This finding highlights the synergy between biogenic synthesis and surface engineering, offering a scalable, eco-friendly solution for the remediation of complex, multi-component industrial effluents.
