Immobilized Cu(ii) and Co(ii) salen complexes on graphene oxide and their catalytic activity for aerobic epoxidation of styrene

Abstract

Novel graphene oxide (GO) tethered Cu(II) and Co(II) salen complexes [M–Salen–GO (M = Cu, Co)] were synthesized via a stepwise procedure and examined as catalysts in the epoxidation of styrene. Acetonitrile was used as a solvent and air as the oxidant in combination with a sacrificial co-reductant isobutyraldehyde. A comparison with homogeneous salen complexes of Co and Cu and graphene oxide (GO) tethered salen complexes was made. Heterogeneous copper(II) and cobalt(II) catalysts were confirmed by X-ray diffraction (XRD), FT-IR, diffusion reflection UV-visible spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), TEM, TG, Raman and XPS. FT-IR, diffusion reflection UV-visible and inductively coupled plasma atomic emission spectroscopy (ICP-AES), along with TG, Raman and XPS results showed that Cu(II) and Co(II) salen complexes were successfully grafted on GO; X-ray diffraction (XRD) and TEM indicated that the sample structures were well preserved. It was found that heterogeneous catalysts were active and showed good recoverability without significant loss in activity and selectivity within successive runs.