A Study of the Thermodynamics of Sorption of Three Direct Dyes on Cellophane Film

Abstract

The sorption isotherms for Direct Red 2, Direct Blue 8, and Direct Yellow 12 were determined at 84° and 95° on cellophane film. The data correlated much better with the Langmuir-type sorption isotherm than with the classical Freundlich equation generally used. Saturation values for each dye are reported at different salt concentrations and temperatures. Enthalpy, standard free energy of sorption, and entropy values were calculated and are interpreted in terms of dye structure and the sorption isotherm used. The Donnan equation was used to calculate gegenion concentrations on the substrate and gave a good representation of the partition of the sodium ion between the film and the solution.