Electronic waste (e-waste) has emerged as a growing environmental concern due to inadequate recycling practices and mismanagement, leading to significant consequences. Repurposing e-waste as an efficient nanocatalyst can be a strategy to mitigate such waste with profound implications. Waste printed circuit boards (WPCBs) may be employed for the recovery of various commercial and precious metals due to the presence of rich elemental compositions. This study explores the potential of WPCBs as a source of metal precursor for the synthesis of nanoparticles (NPs) using a biological approach wherein cell-free culture supernatant (CFCS) is employed.

The main objective of this work was to biosynthesize metal NPs using WPCBs and to evaluate the catalytic activity of the NPs. The biosynthesized NPs were characterized by X-ray diffraction analysis, FESEM, FTIR, TEM, and SAED and fringe patterns, which suggested the formation of Cu_xO NPs. FESEM and TEM analyses revealed that the NPs are spherical in shape. FTIR analysis identified the presence of copper oxide and organic functional groups of biological origin, which indicated the action of metabolites present in the CFS as capping agents to stabilize the NPs. The catalytic activity of the Cu_xO NPs was evaluated using a model reaction involving the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride (NaBH₄) as a reducing agent. The synthesized NPs exhibited excellent catalytic activity, and the reduction reaction was found to follow the pseudo-first-order kinetics.