Adsorption study of dimethylaminostyryl benzazoles onto Na-montmorillonite

The adsorption of 2-(4′-dimethylaminostyryl)benzoxazole (DMASBO) and its benzothiazole analogue (DMASBT) onto Na-montmorillonite (Na+-MMT) was studied. The adsorption data have been fitted with Freundlich and Dubinin–Radushkevich (D–R) equation to find the characteristic parameters of each model. From D–R isotherm, it was concluded that the adsorption is of chemical nature. The equilibrium adsorption constant, Kc, was determined and has been used to calculate the enthalpy and entropy of the adsorption process. The mechanism of the adsorption has been investigated by fluorescence, IR, X-ray and ESR spectroscopic measurements. These measurements indicate oxidation of the styryl dyes by the Lewis acidic sites of the clay and formation of radical cations at Na+-MMT surface without intercalation into the interior.