Different Types of Paramagntic Complexes and Size Manifastation in Epr Measurments of Small Carbon Particles

Two kinds of microporous activated nanostructured carbons were studied by electron paramagnetic resonance (EPR) spectroscopy. They have different specific surface areas: 1500 m2/g (AC I) and 2500 m2/g (AC II). It was observed that the EPR spectra shapes and their temperature evolution between 300 K and 4 K were depending on the types of carbon sample. Roomtemperature spectra show dissimilar line-widths ΔB = 0.5 mT and 1.6 mT for AC I and AC II, respectively. The AC I carbon EPR spectra show: (a) a broadening at the beginning of the cooling process, similar to the EPR behavior of graphite and, subsequently and (b) a quick narrowing below 130 K. For the super-activated carbon (AC II), a monotonic narrowing process is observed on decreasing the temperature. These different behaviors were attributed to the size manifestation of graphenes in both activated carbons.