Engineering Active Sites in Reduced Graphene Oxide: Tuning the Catalytic Activity for Aerobic Oxidation

Abstract

[EN] The influence of the graphene oxide (GO) reduction method on the activity of the resulting reduced graphene oxide (rGO) for the aerobic oxidation of benzylamine is reported. Starting from GO obtained by the Hummers method, a series of rGO samples were obtained either by chemical (hydroquinone (HQ), hydrazine (HZ) or ascorbic acid (ASC)) or by thermal reduction were prepared. Analytical and spectroscopic techniques provide evidence showing that chemical reducing agents reduce GO with different functional groups that influence the catalytic activity of the resulting rGO for the activation of molecular oxygen in benzylamine oxidation. The highest activity in the aerobic oxidation of benzylamine at 80 degrees C was found for the rGO-HQ1 sample prepared using HQ as a reducing agent. It is proposed that HQ introduces hydroquinone/p-benzoquinone-like moieties on the graphene sheet that act as active sites in the oxidation reaction. This proposal is supported by the activity of HQand/or p-benzoquinone as organocatalysts and by selective masking of oxygen-functional groups present in the most active rGO sample. The most active rGO sample exhibited good reusability and stability in five consecutive uses. Selective quenching experiments revealed that hydroperoxyl radicals are the primary reactive oxygen species generated in the system.