Estimation of the parameters of the microporous structure of active carbons from the pulsed-field NMR data and the adsorption of nitrogen and water vapors

The adsorption of nitrogen vapors is investigated at 77 K, and that of wate r vapors at 293 K, using three samples of active carbons (AC) with differen t degrees of activation; the parameters of the microporous structure of AC are determined from these adsorption data. The same samples are used to mea sure the NMR relaxation, and to determine the self-diffusion coefficients o f the water and benzene molecules. An analysis of the NMR signals using the "solid-echo-free induction decay" and the Carr-Purcell-Meiboom-Gill sequen ces Showed that the multiexponential pattern of decay of the nuclear-magnet ization is associated with the presence of adsorbed molecules in different states-"phases". The exchange processes between the "phases" with different relaxation times are investigated using the Goldman-Shen sequence. It is s hown that a molecular exchange occurs between the pores of different sizes or between different regions of porous structure. A method is proposed to e stimate the pore size by the NMR data. When investigating the self-diffusio n of the adsorbed molecules of water and benzene using the pulsed-field gra dient NMR, the sizes of nonuniformities of the porous structure in the gran ules of active carbons are estimated. The NMR data are found to be consiste nt with the results of adsorption measurements.