Copper nanocluster-mediated degradation of toxic organic dyes: a sustainable approach to water remediation

Abstract

Organic pollutants, particularly toxic dyes discharged in large quantities by the textile and food industries, have attracted considerable scientific attention due to their environmental persistence and detrimental effects. Metal nanoclusters (NCs), owing to their redox-active metal cores and tunable surface properties, represent promising candidates for the efficient degradation of such pollutants. In this study, we report an efficient protocol for the degradation of Rhodamine B (RhB) and Methylene Blue (MB) using cysteine-capped copper nanoclusters (Cys-Cu NCs) in the presence of hydrogen peroxide (H₂O₂), without any external stimuli. The degradation, carried out under neutral pH and aqueous conditions, was monitored using UV-visible spectroscopy and showed approximately 97% degradation of both dyes (20 µM) within 90 minutes, accompanied by complete decolourization of the solutions. Characterization of the degradation products using LC-MS, ¹H NMR, and ion chromatography confirmed the complete mineralization of the dyes into non-toxic species. Control and free-radical scavenging experiments confirmed that the process proceeds through the synergistic action of Cys-Cu NCs and H₂O₂, primarily involving reactive oxygen species (ROS) such as hydroxyl (˙OH) and superoxide (˙O₂⁻) radicals, thereby elucidating the underlying degradation mechanism. Comparative studies with other metal nanoclusters highlight that the superior activity of Cys-Cu NCs arises from the intrinsic redox property of copper, which plays a pivotal role in ROS generation and dye degradation. Kinetic analyses revealed that RhB and MB follow distinct degradation pathways. Furthermore, degradation studies performed at varying dye concentrations, larger reaction volumes, and in real water samples demonstrated the robustness and practical applicability of the developed method. Overall, the Cys-Cu NC-mediated degradation offers a sustainable and efficient approach for the remediation of dye-contaminated water.