Magnetic Properties and Interplay between Nanographene Host and Nitric Acid Guest in Nanographene-Based Nanoporous Carbon

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Magnetic properties of nanoporous carbon consisting of a 3D disordered network of nanographite domains are investigated in relation to the host–guest interaction with guest nitric acid molecules possessing significant oxidizability. An individual nanographite domain consists of a stack of 3–4 nanographene sheets, the edges of which have the localized spins of nonbonding edge states. The adsorption of HNO3 induces a two-step reduction in the edge-state spin concentration due to the charge-transfer interaction and is accompanied with the decomposition of HNO3 into the magnetic NO molecules, which are dimerized to form nonmagnetic (NO)2 with an enthalpy of ≈35 kJ mol−1 at low temperatures. The electronic activities of the edge state play an important role in the decomposition effect, and the NO spins are coupled to the edge-state spins through exchange interaction. The NO molecules can be removed by vacuum heat-treatment above 200 °C, however the nitrogen-containing functional groups strongly incorporated on the nanographene sheets cannot be removed even at such high temperature.
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