Multifunctional copper–glutathione clusters with superior <i>p</i>-nitrophenol degradation and horseradish peroxidase-like activity

Copper nanoclusters (Cu NCs) are emerging as highly promising nanomaterials due to their unique physicochemical properties, making them an ideal platform for catalysis, sensing, and environmental remediation. This study explores the development of ultrasmall, water-soluble copper-glutathione (Cu-SG) nanoclusters, focusing on their catalytic capacity for the degradation of <i>p</i>-nitrophenol (<i>p</i>-NP), horseradish peroxidase (HRP)-like activity, and hydrogen peroxide (H₂O₂) detection. During synthesis, a combination of one-pot synthesis and acid-etching strategy was employed. The acid-etching approach was specifically utilized as an essential method to precisely regulate the structural properties of the clusters. The water-soluble ultrasmall Cu-SG nanoclusters show superior catalytic efficiency, achieving 98% conversion of <i>p</i>-NP to <i>p</i>-aminophenol (<i>p</i>-AP) within six minutes. The reaction followed first-order kinetics with a rate constant of 0.44 min^-1, consistent with the Langmuir-Hinshelwood model. Notably, the Cu-SG retained catalytic efficiency across multiple reaction cycles, highlighting their recyclability and long-term stability. Additionally, Cu-SG exhibited excellent sensitivity and selectivity for rapid colorimetric H₂O₂ detection due to the strong HRP-like activity, achieving a detection limit of 6.03 μM with high resistance to interference from other ions and compounds. Thermodynamic analysis demonstrates an enthalpy driven spontaneous reduction of <i>p</i>-NP with Cu-SG, wherein the van der Waals and hydrogen bonding interactions are predominant. By contrast, the interaction of Cu-SG with H₂O₂ is an entropy-driven, spontaneous process, and the dominating hydrophobic forces drive the HRP-like catalytic mechanism. This study demonstrates the potential of the Cu-SG as an efficient, stable, and recyclable water-soluble copper nanocatalyst for pollutant degradation and as a sensitive sensor for reactive species.