Nanotechnology and nanomaterials

The study of adsorption and desorption properties in nanostructured pyrolyzed material (coal) by EPR method
S.V. Krasnovyd1, A. A. Konchits1, B. D. Shanina1, A. N. Molchanov2, A. A. Kamchatnyj2
1Department of Optics and Spectroscopy, Institute of semiconductor Physics, Natl. Acad. of Sci. of Ukraine. Prospect Nauki, 45, Kiev-03028, Ukraine
2Institute for Physics of Mining Processes,Natl. Acad. of Sci. of Ukraine,Str. Simferopolska, 2a,Dnipro-49600, Ukraine
       The electron paramagnetic resonance (EPR) method is very informative for research of influence molecular oxygen to paramagnetic centres in porous carbonaceous materials [1]. The sensitivity of samples to oxygen can be used both to study the adsorption properties of the carbon surface, and to create of sensors to control the partial oxygen content in animal or human tissues [2].
       In this work the pyrolyzed samples of gas types coal were obtained by vacuum annealing at T= 700 0C and studied by EPR method. The strong broadening of the EPR line up to 200-300 G without the use of chemical reagents for activation the surface of coal was observed for the first time. It was found that the width of the EPR line strongly depends on the partial pressure of molecular oxygen. To study the adsorption-desorption processes on the carbon surface, we studied the EPR characteristics of pyrolyzed samples under the conditions of the replacement of pre-adsorbed oxygen with nitrogen and vice versa. The EPR line width was increased from 15 G to 250 G with replacing molecules N2 to O2 and decreased from 250 G to 15 G with replacing O2 to N2. The concentration of paramagnetic centres Ns remains stable at least in the range of oxygen partial pressures from 0 to 20%. 
        In general, the analysis of EPR data showed the high sensitivity pyrolyzed samples coal to molecular oxygen. The samples demonstrate both a high adsorption capacity with respect to oxygen and the dramatic effect of moisture on these processes.

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