Biosynthesis of copper nanoparticles supported on manganese dioxide nanoparticles using Centella asiatica L. leaf extract for the efficient catalytic reduction of organic dyes and nitroarenes

Abstract

In this study we designed a novel, cost-efficient and green method for the synthesis of copper nanoparticles (Cu NPs) supported on manganese dioxide (MnO2) NPs, using Centella asiatica L. leaf extract as a naturally-sourced reducing agent, without stabilizers or surfactants. This synthetic process is environmentally-friendly and avoids the use of toxic reducing agents. Phenolic hydroxyl groups in the leaf extract are believed to reduce Cu2+ in solution to generate Cu NPs that are subsequently stabilized on the MnO2 NP surfaces. The resulting Cu/MnO2 nanocomposite was fully characterized using X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. This material was found to function as a highly active, efficient and recyclable heterogeneous catalyst for the reduction of Congo red, rhodamine B and methylene blue as well as nitro compounds such as 2,4-dinitrophenylhydrazine and 4-nitrophenol in the presence of NaBH4 in aqueous media at ambient temperature. The high stability of the Cu/MnO2 nanocomposite also allows the catalyst to be separated and reused several times without any significant loss of activity.