Thermodynamics of the Adsolubilization Equilibrium of Rhodamine B by Surfactant-Modified Zeolites

The adsolubilization of the cationic dye rhodamine B (RB) into the adsorbed layers of dodecyl- (DTAB) and tetradecyltrimethylammonium bromide (TTAB) on high silica mordenites (HSZ-1, HSZ-3) and P-type zeolite (PZ) was examined quantitatively. The adsolubilization constant for the HSZ-1/TTAB system was determined at temperatures from 10 to 40 °C. As the surfactant adsorption increased, the adsolubilization of RB by the zeolite/surfactant complexes was enhanced. Adsolubilization of RB by HSZ-3/surfactant complexes required a critical quantity of adsorbed surfactant, whereas the PZ/TTAB complex needed only a very small quantity of adsorbed TTAB to adsolubilize RB. Both the adsolubilization constant and the maximum capacity were calculated using a Langmuir-type equation, and the enthalpy and entropy changes were determined for the HSZ-1/TTAB mixed system. The difference in the adsolubilization mode of the three zeolite/surfactant complexes is discussed in relation to the aggregation mode of the cationic surfactant.