Green Synthesis of Ag/Cu–Zn Plasmonic/Non‐plasmonic Heterojunction Nanoparticles for Sunlight‐Driven Photodegradation of Methyl Orange

The rapid increase of industrialization, especially in textile and dyeing, which releases azo dye (methyl orange) contaminants into the environment, has raised a serious concern for human health. Therefore, the development of sustainable, high-efficiency wastewater treatment technologies to mitigate the environmental impact of organic pollutants is highly required. In this study, the eco-friendly, biogenic synthesis of a novel silver/copper-zinc (Ag/Cu-Zn) plasmonic/non-plasmonic heterostructure was achieved using Ocimum Lamiifolium plant extracts as reducing agents and tannic acid as a stabilizing agent. To optimize the synergistic interaction of heterostructures between plasmonic and non-plasmonic metals, Job’s Method was employed. This method provides the optimum stoichiometry of Ag/Cu to Zn, which helps to optimize surface area and energy level modulation, and maximum photocatalytic enhancement was achieved. The properties of the nanoparticles were studied using different spectroscopic and microscopy techniques. The analyses confirmed the successful synthesis of the small-sized nanoparticles with spherical and quasi-spherical structures and in the zerovalent state. The photocatalytic performance was evaluated through the degradation of methyl orange (MO) dye under natural sunlight irradiation. The optimized Ag/Cu-Zn heterostructure exhibited superior photocatalytic performance with 99.3% degradation at pH 2, 10 ppm MO concentration, and 0.01 g/L nanoparticle dosage within 30 min of sunlight irradiation. The plasmonic noble metal coupled with a non-plasmonic resulted in an efficient transfer of energetic hot electrons to the non-plasmonic conduction band; enhanced light harvesting across a broad spectral range; improved separation of electrons and holes, and increased generation of reactive species, resulting in an enhanced photocatalytic reaction. The effect of different scavengers was examined, and the results indicate that O₂•− radicals are the main contributors to the enhanced photocatalytic performance of the system. The degradation rate of MO using the nanoparticles followed pseudo-first-order kinetics and was greatly influenced by the studied parameters. This research demonstrates that the integration of biogenic synthesis with stoichiometric optimization via Job’s method and plasmonic-non-plasmonic heterojunction provides a robust pathway for fabricating high-performance, visible-light-active photocatalysts for environmental remediation.