Biosynthesis of copper(II) oxide nanoparticles using Murayya koeniggi aqueous leaf extract and its catalytic activity in 4-nitrophenol reduction

Copper(II) oxide nanoparticles (CuO NPs) have a wide range of applications as catalysts. The natural abundance of copper and its relatively low cost make it a viable alternative to catalysts that made from expensive precious metals such as platinum and palladium. In this study, a rapid, simple and green method was developed for the synthesis of CuO NPs using an aqueous extract of Murayya koenigii leaves. Several parameters were optimized, namely, the volume of leaf extract, pH, reaction temperature and reaction time. The optimum condition for the biosynthesis was obtained by using 3 mL of leaf extract; 10 mL of 5 mM CuSO4, at pH 11, at room temperature. The biosynthesis was completed within 50 minutes. The synthesized CuO NPs were characterized using Ultraviolet-visible Spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Transmission Electron Microscope (TEM) analyses. The UV-Vis absorption spectra confirmed the formation of CuO NPs with characteristic peak at 634 nm. The FTIR spectroscopic analysis of the biosynthesized CuO NPs confirmed the surface adsorption of the bioactive components in the leaf extract that acted as the reducing agent and stabilizing agent for the metal nanoparticles. XRD analysis showed a series of diffraction peaks at 2. of 32.5 degrees, 35.5 degrees, 38.6 degrees, 48.8 degrees, 53.4 degrees, 58.1 degrees, 61.5 degrees, 66.3 degrees, 68.0 degrees, 72.4 degrees and 75.0 degrees, corresponding to (110), (002), (111), (202), (020), (202), (113), (311), (220), (311) and (222), respectively. From TEM images, CuO NPs were of spherical shape with a mean diameter of 8.4 nm. The biosynthesized CuO NPs demonstrated good catalytic activities on the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of sodium borohydride, NaBH4 and could be reused three times without significant decreases in the catalytic activities.