Functional group dependence of spin magnetism in graphene oxide

Abstract

We evaluated graphene oxides (GOs) synthesized by different methods in terms of magnetism and chemical structure. GO samples were synthesized by Brodie and Hummers methods, which are labeled as BGO and HGO, respectively. The temperature dependence of magnetic susceptibility indicates an order of magnitude larger localized spin concentration of HGO (Ns=2×1019) than that of BGO (Ns=2×1018). The FT-IR spectra for GO exhibits peaks for hydroxyl, carboxyl, epoxy and carbonyl groups in spite of absence of any peak for graphite. Interestingly, the peak around 1224cm−1 attributed to COH stretching for HGO is larger than that for BGO, while the peak around 1050cm−1 for COC stretching is larger for BGO. The difference of functional groups between HGO and BGO explains the larger spin magnetism for HGO. In the case of introduction of epoxy group, oxygen atom bonds to adjacent carbon atoms, remaining symmetry regarding A, B sub-lattices of graphene lattice. On the other hand, attaching hydroxyl group occurs randomly on carbon atoms of graphene and breaks symmetry of A, B-sublattices, resulting in the emergence of the localized states and the spin magnetism.