Extracellular synthesis of heteroatom doped copper oxide nanoparticles from electronic waste – Transforming waste to resource for the remediation of nitrophenol contaminated water

Abstract

Industrial effluents containing hazardous phenolic compounds such as 4-nitrophenol (4-NP) can threaten aquatic ecosystems and the environment. To address the environmental issues due to nitrophenol-contaminated industrial effluents and rapidly generating electronic waste (e-waste), catalytic nanoparticles are biosynthesized utilizing the waste printed circuit boards (WPCBs) and the cell-free supernatant (CFS) of the bacteria Alcaligenes aquatilis for the catalytic reduction of 4-NP with sodium borohydride (NaBH4). The optimum synthesis parameters to maximize 4-NP reduction were an initial pH of 12.4 and a volume ratio of metal leachate to CFS of 1:3. These nanoparticles were found to be heteroatom-doped CuO/Cu2O (Bio-CuO/Cu2O-PCB) with spherical shape, average crystallite size of 19 nm and average particle size of 19.2 nm. The biosynthesized nanoparticles exhibited excellent catalytic activity in the reduction of 4-NP with a pseudo-first-order rate constant (kapp) of 0.526 min-1, induction period of 2 min, and 90% reduction of 4-NP in 6 min. This work demonstrates the recovery of metal resources from waste as nanoparticles with excellent catalytic activity using a green, eco-friendly synthesis method under ambient conditions. Bio-CuO/Cu2O-PCB showed better activity than commercial CuO, biosynthesized and chemically synthesized CuO using precursor salt. The developed synthesis method is eco-friendly and could yield a recyclable catalyst for reducing harmful aromatic pollutants such as 4-NP present in wastewater to 4-aminophenol, a pharmaceutical intermediate.