ИСТИНА

Carbon materials are widely applied in the field of filtration of gaseous and aqueous media. Nowadays nanomaterials with tunable surface properties attract a lot of research interest. The selectivity of adsorption of desirable pollutants can be improved by introducing heteroatoms in graphene layers. The aim of this work was to determine the heat of sorption of acetone, ethyl acetate, toluene and acetic acid on carbon nanomaterials surface. Two types of carbon structures were selected: carbon nanotubes (CNT) and carbon nanoflakes (CNF). Carbon nanomaterials were obtained by pyrolysis of benzene (pristine CNT and CNF) and acetonitrile (N- CNT and N- CNF). Pristine CNT and CNF were oxidized by concentrated nitric acid for 4 hours. Structure and homogeneity of obtained materials were confirmed by SEM, TEM and thermal analysis methods. Chemical state of N and O atoms was identified by XPS method. Adsorption properties of carbon were studied by DVS Advantage instrument (SMS, UK). Dry nitrogen carrier gas with vapours of compound under investigation passed over the carbon sample at well-defined flow rate and temperature. The sample mass readings from the microbalances revealed the vapour adsorption/desorption behaviour of the material. Experimental heats of sorption of all the solvents were calculated after measurements at 20 and 30C according to: . It was shown that in the case of CNF the heat of sorption of studied vapours increases with the increase of dipole moments from 34,6 to 39,2 kJ/mol, therefore CNF is the most suitable material for polar substances sorption. For adsorption of benzene-rings containing substance such as toluene the best sorbent is CNT. Nitrogen-doped materials behaved the best way in the sorption process of acetic acid, as their functional NH2 groups reveal basic properties. The oxidation of materials lead to the formation of carboxy, ether and other surface functional groups. It was found that the heat of sorption of studied vapours on oxidized surface is higher than on both pristine and nitrogen-doped materials. The adsorption capacity on the contrary decreases after oxidation that is caused by the reduction of porosity and elimination of structure defects. The adsorption capacity of CNT, N-CNT and N-CNF calculated from micropores volume varies from 5 to 6 mg/g at 20С, pristine CNF are found to be mesoporous sorbent and for oxidized materials the value of adsorption capacity did not exceed 2 mg/g. Acknowledgments The reported study was funded by RFBR according to the research project № 18-33-00322.