An efficient CuO/rGO/TiO2 photocatalyst for the synthesis of benzopyranopyrimidine compounds under visible light irradiation

Abstract

In this study, we report on the preparation of a copper oxide/reduced graphene oxide/titanium dioxide (CuO/rGO/TiO₂) photocatalyst and its application in a coupling reaction for carbon–nitrogen bond formation under visible light irradiation. The CuO/rGO/TiO₂ nanocomposite was synthesized from graphene oxide, Cu and Ti precursors and was fully characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), cyclic voltammetry (CV), UV-vis absorption, and photoluminescence (PL) spectroscopy. The photocatalytic effectiveness of the CuO/rGO/TiO₂ nanocomposite was explored in a pseudo 4-component reaction of salicylaldehyde, malononitrile and secondary amines for the preparation of benzopyranopyrimidines in high yields (75–95%) under visible light irradiation (60–120 min) in ethanol as the solvent at room temperature. Furthermore, the photocatalytic activity of the CuO/rGO/TiO₂ nanocomposite was studied in a domino reaction for the coupling of salicylaldehyde and malononitrile in the presence of other aldehydes and secondary amines under the same reaction conditions to afford the corresponding benzopyranopyrimidine derivatives in 77–93% yields after 120–180 min. The reusability investigation of the CuO/rGO/TiO₂ photocatalyst showed that it could be recovered and recycled for 5 runs without a significant decrease in its catalytic activity.