Ultrasonic-assisted green synthesis of β-amino carbonyl compounds by copper oxide nanoparticles decorated phosphate functionalized graphene oxide via Mannich reaction

Abstract

Highly efficient and active CuO nanoparticle decorated Phosphate functionalised graphene oxide (PGO-CuO) nanocomposite has been synthesized in a water-isopropanol system and used as an active catalyst for the synthesis of β-amino carbonyl compounds via Mannich reaction by using a greener ultrasonic method. • CuO nanoparticles were decorated on PGO via a simple wet chemical synthetic route. • PGO-CuO catalyst was thoroughly characterized by various analytical techniques. • A greener ultrasonic route was used for synthesis of β-amino carbonyl compounds. • Higher catalytic efficiency was obtained under solventless condition. • The catalyst could be recycled for six times without any effective loss in activity. A facile chemical synthetic route has been demonstrated for the synthesis of copper oxide nanoparticles decorated phosphate functionalized graphene oxide (CuO/PGO). The synthesized nanocatalyst was used as an efficient and active candidate for the synthesis of β-amino carbonyl compounds via a green synthetic ultrasonic route. The structural properties of the samples were investigated by means of a number of sophisticated techniques like X-ray diffraction (XRD), Fourier-transform Infrared (FTIR) spectroscopy, High Resolution Transmission Electron Microscope (HRTEM), N 2 adsorption-desorption measurements, X-ray photoelectron spectroscopy (XPS) analysis, Ammonia temperature programmed desorption analysis (NH 3 -TPD) and Raman spectroscopy. HRTEM analysis confirmed the presence of spherical CuO nanoparticles distributed uniformly throughout the PGO surface. XPS analysis demonstrated the presence of Cu 2+ species and minor reduction of oxygen functional groups on GO. A higher surface area of 162 m 2 /g for CuO/PGO was found from N 2 adsorption-desorption isotherms. Later on, the presence of acidic groups on CuO/PGO that play an essential role in the catalytic activity was examined by NH 3 -TPD and pyridine adsorbed IR analysis. The total acidity on the surface of synthesized nanocatalyst was found to be of 0.59 mmol g −1 which includes both Lewis as well as Brönsted acidic sites. A higher product yield of 95% in a shorter period of time of 15 min was achieved which is superior to many reported catalytic systems. A combined strategy involving greener and easier ultrasonic route and use of an efficient acidic graphene oxide-based catalyst resulted in higher catalytic activity and stability with good recyclability.