吸附在活性炭上的二氧六环类固相和类液相性质的NMR研究

The NMR Study of the Solid and Liquid Like Phases of Dioxane Adsorbed on Charcoals

In this paper a study of the spin lattice relaxation times of dioxane(DO) adsorbed on various charcoals is presented. Results show that the magnetziation of DO decays biexponentially (Table 1) as observed in the case of adsorbed hydrocarbons~6]. The fast relaxing molecules are considered to be those adsorbed in micropores with radii less than 1.0 nm whose motion is restricted and slowed down, thus they form a solid like phase. However, the slow relaxing ones are those condensed in the micropores, they are free to move and form the liquid like phase. Molecules condensed in the interior of the micropores exchange rapidly with those situated in the vicinity of the pore wall according to Eq.(2).Comparison of data in Table 1 may lead to a conclusion that charcoal with greater density of surface acidic groups and greater percentage of pore capacity with radius<1.0 nm (V_(10)/V_(30)) has a greater percentage of solid like phase (P_f). Although V_(10)/V_(30) of density of surface acidic groups. It is apparent that surface acidic groups in micropores play an important role in the formation of solid like phase of DO on charcoals. It seems that DO form hydrogen bond with the surface acidic groups. It is this hydrogen bond and the hinderance effect of pores restrict the DO from moving freely, which results in the formation of the so called solid like phase. It can be found from small (0.10 ml/gC). This implies that DO vapour may first condense in the micropores having more acidic groups and higher activation energy, and then fill in other pores step by step as the adsorption process proceeds.