Features of nuclear magnetic relaxation of water and benzene molecules during absorption on activated carbons and estimation of pore size distribution in adsorbents

Nuclear magnetic relaxation in activated carbon-water and activated carbon-benzene adsorption systems was studied by pulse NMR methods. Activated carbons characterized by different porous structures and chemical state of the surface were used. The application of the three-pulse Goldman-Shen sequence to the adsorption system generates a dipole echo caused by the dipole-dipole coupling of "structural" protons, which is not averaged due to their mobility during experiment. The non-exponential character of relaxation attenuations of the transverse and longitudinal nuclear magnetizations of physically adsorbed molecules in activated carbon pores is a result of differencies in pore sizes. The pore sizes in activated carbon and the size distribution were determined from the data of nuclear magnetic relaxation with allowance for the contribution from the "structural" protons.