Magnetism of HNO3-adsorbed nanoporous network of nanographene sheets

Nonbonding π-electron states (edge-state) localized at the graphene edges are the origin of electronic/chemical activities of nanographene, and the localized spin of this edge state gives unconventional magnetic features to nanographene. The magnetic properties of nanoporous carbon consisting of a 3D disordered network of nanographite domains (each consists of a stack of 3–4 nanographene sheets) are investigated in relation to the host-guest interaction with nitric acid molecules possessing significant oxidizing power. The adsorption of HNO3 molecules induces a two-step reduction in the edge-state spin concentration due to the charge transfer from nanographene to HNO3 molecules; charge transfer with the exterior nanographene sheets of the nanographite domain in the first step, and subsequent intercalation into the interior nanographene sheets in the second step. Besides the charge transfer reaction, it is found that the paramagnetic NO molecules are produced owing to the decomposition of HNO3 and they are dimerized to form nonmagnetic (NO)2 at low temperatures. This finding suggests that the chemically active nanographene having edge states plays an important role in enhancing charge transfer and the concomitant decomposition of the guest HNO3 molecules. ► Edge-state at zigzag edges gives electronic/chemical activities of nanographene. ► Charge transfer interaction happens between HNO3 and edge-state spins. ► HNO3 induces a two-step reduction in the edge-state spin concentration. ► Paramagnetic NO molecules are created and dimerized to form nonmagnetic (NO)2. ► Edge state and nanopores enhance the dimerization.