Nanocomposites and nanomaterials
Effect of organic solvent and transition metal ions on the paramagnetic properties of actvated carbon studied by EPR. 
A.K. Melnyk 
Institute for Sorption and Problems of Endoecology, NAS of Ukraine. Naumov str.,13, Kyiv- 03164, Ukraine
E-mail: mak106@ukr.net

Activated carbons, first of all nano- and microporous ones, are the class of materials possessing outstanding physicochemical properties. They are effective adsorbents, hydrogen storage media and, besides this, widely used as an electrodes for supercapacitors. Nevertheless, their paramagnetic properties and potential for use as a specific probes and sensors are relatively poorly studied.
In our current work, we focused primarily on the peculiar features of the paramagnetic properties of activated carbon in suspensions, which are mainly determined by the formation of high concentration of dangling bonds during activation process. In “dry” condition (being exposed to air), unpaired electrons of AC dangling bonds interact with molecular oxygen, incorporated into carbon matrix, that leads to the substantual lowering of spin-spin relaxation times. In suspension diffusion of diamagnetic organic solvent into the nano- and micropores removes oxygen molecules and principally changes the surrounging of unpaired electrons and therefore spin density delocalization and relaxation properties – samples become suitable to research using electron paramagnetic resonance spectroscopy (EPR).
During our experiment, suspensions of several commercially available samples of charcoal with preferential pore diameter of 5-100 angstrom and total surface values ranging from 600 to 1700 m2/g were studied using continuos wave EPR. Spectra of all samples consist of singlet line with g factor values of 2.001÷2.005 and peak-to-peak linewidth from 0.6 (in the case of mostly graphitized carbon) to 10 mT (less polycyclic aromatic, more aliphatic fragments). It was shown that both effective values of g and ΔH depend on the particular organic solvent chosen (due to the changes in local environment of unpaired electrons), the greatest effect was observed in strongly graphitized samples. A weaker dependence of the characteristics of the spectral line was observed with a change in pH and the introduction of alkali metal ions into the solution (changes in the second case were present only for high concentrations). Extra sensitivity to some transition metal cations (Cu2+, Fe3+, Ni2+, Co2+) in solution could be explained by the spin exchange and/or dipole-dipole mechanism. In this case, such interactions led mainly to a decrease in the intensity of the EPR, which was observed up to a millimolar concentration of ions.