Adsorption and kinetic studies of the intercalation of some organic compounds onto Na+-montmorillonite

The adsorption and the kinetics of the intercalation of metanil yellow dye, p-aminodiphenylamine (p-NH2-DPA), and benzidine by colloidally dispersed Na+-montmorillonte (Na+-MMT) have been studied. The adsorption isotherm parameters confirmed the occurrence of chemical adsorption that is based on the cation-exchange process. The selectivity of these compounds toward Na+-MMT follows the order metanil yellow < p-NH2-DPA < benzidine, which reflects the stability sequence of the intercalates. The attainment of sorption equilibrium and the diffusion coefficient follows the order metanil yellow > p-NH2 -DPA > benzidine. The rate of oxidation has been quantitatively measured using a stopped-flow spectrophotometer. The rate constant follows the order benzidine < p-NH2-DPA < metanil yellow. Addition of allyle acetate shows inhibiting effect on the reaction rate. The rate of cation exchange process between the radical cation of the organic molecule and the Na+-ion in the Na+-MMT has been monitored by using the stopped-low instrument with an electrical conductivity detection unit. The activation energy of the electron transfer reaction is less than that of cation exchange process and has the order metanil yellow < p-NH2-DPA < benzidine. X-ray diffraction, IR, and differential scanning colorimetry (DSC) measurements confirmed the intercalation process. (C) 2002 Elsevier Science.