Nanoparticles of low-functionalized fullerenols as stable radicals: towards dispersed nanocapacitors and nanobatteries?

In this work, we have prepared a stable organic dispersion of fullerenols with low degree of modification and without passivant agents and a metastable aqueous dispersion with the same material. Fullerenols were prepared by reacting pristine fullerene C60 with potassium hydroxide in organic medium under inert atmosphere. In this step, radicals of fullerene and fullerenols are formed. Air exposition promotes oxidation of most of those charges and induce material aggregation as nanoparticles in organic liquid, which are indefinitely stable due to electrostatic and solvation interactions. Fresh oxidized mixture was transfer to water and resulted in metastable aqueous dispersions. The prepared organic and aqueous dispersions are formed by fullerenol nanoparticles with mean hydrodynamic sizes of 74 and 86 nm (both polydispersed) and zeta potentials of -60 and -34 mV, respectively. Additional characterization provided evidences for fullerene modification with hydroxyl groups and approximately stoichiometry of K1.59[C60(OH)13.15] for those nanoparticles. Even being sensible to oxygen, some of those radicals remain stable in the fullerenol nanoparticles as probed by electron paramagnetic resonance spectroscopy (EPR). We postulate that these stable radicals are responsible for the measured zeta potential and for the electrostatic interactions in organic liquid. Fullerenol aqueous dispersion was deposited by drop casting on glassy carbon electrode and dried at room temperature. Cyclic voltammetry (CV) in KCl presents one peak in the cathodic region, which is present in similar samples and it is attributed to one-electron reduction. No correspondent oxidation peak was observed, indicating charge stabilization. CV results also suggest that the materials surface is not highly modified by hydroxyl groups corroborating with the previous analysis, and that those charges formed in KCl affects the response specially using negatively charged redox probes. Since fullerenol nanoparticles have remaining radicals, we have been carried out experiments to use this reservoir of electrical charges in chemical reactions or to perform useful work, therefore such nanoparticles could be further explored as dispersed nanocapacitors and/or nanobatteries.