Band bending caused by forming heterojunctions in Cu-Cu2O/rGO-NH2 semiconductor materials and surface coordination of N-methylimidazole, and the intrinsic nature of synergistic effect on the catalysis of selective aerobic oxidation of alcohols

Abstract

In this work, three materials of Cu-Cu2O/rGO-NH2-4.4/1, -1/1 and -1/10.4, in which the numeric suffices denote the ratio of Cu/Cu2O in the materials, were described and characterized using various analytical techniques including FTIR, XRD, SEM, HRTEM, XPS and Raman spectroscopy. To probe the band structures of these materials, UPS, cyclic voltammetry, and UV–vis reflection spectroscopy were also employed. The formation of heterojunctions in the ternary materials tune their band structures by raising the energy level of valence band maximums (VBMs), inducing an internal electric field (IEF) and an electron accumulation layer (EAL) within the materials. Augment of copper content in the materials can enhance the energy level rising. The coordination of N-methylimidazole (NMI) with Cu2O of the materials can also contribute to raising the energy level. The changes in these electronic properties bring about a synergistic effect in selective aerobic oxidation of benzylic alcohols via improving O2 activation and facilitation of electron transfer between the catalyst and the reactants due to the rising of the energy level of VBM and the formation of IEF.