Kinetic and Mechanistic Insights into the Catalytic Reduction of 4-Nitrophenol, a Priority Water Pollutant over Cu _<i>x</i> O/Cu Multi-Metallic Nanocomposite Derived from Waste Printed Circuit Boards

Recovering metals from electronic waste through urban mining is a cornerstone of sustainable environmental management. In this study, Cu x O/Cu-multimetallic nanocomposites (Cu x O/Cu-MMN) were synthesized from waste printed circuit boards (WPCBs) via extracellular synthesis using Alcaligenes aquatilis . The Cu x O/Cu-MMN particles were 12.7 nm in size and consisted of Cu, CuO, Cu 2 O, and other metals in oxides/elemental form. They were catalytically active in the reduction of 4-nitrophenol, a priority pollutant listed by the United States Environmental Protection Agency (USEPA), using NaBH 4 . The reaction followed pseudo-first-order kinetics with an activation energy of 27.9 kJ/mol. The thermodynamic parameters, such as changes in activation enthalpy (Δ H # ), entropy (Δ S # ), and Gibbs free energy (Δ G # ) were determined. The reduction process followed Langmuir–Hinshelwood mechanism, involving the competitive adsorption of both the reactants on the surface of Cu x O/Cu-MMN, followed by electron transfer. The resource recovery from WPCBs as a catalyst for wastewater treatment, supports circular economy and Sustainable Development Goals.