Adsorption Equilibria of Cationic and Anionic Azo Dyes and their Ion Associates at Water/Organic Solvent Interface

Abstract

The interfacial adsorption equilibria of cationic and anionic dyes and ion associates formed between them were examined. A high-speed stirring apparatus was used for mixing of water and organic solvent. Phase separators with poly (tetrafluoroethylene) (PTFE) membrane and filter paper were used to separate an organic phase and an aqueous phase, respectively. The concentrations of species in each bulk phase were measured by absorptiometry. Four analogues of 1-alkyl-4-[4-(dialkylamino)phenylazo]pyridine, Methylene Blue and four analogues of Methyl Orange were examined. Chloroform, styrene, benzene and cyclohexane were used as organic solvents. Under vigorously stirring conditions, the interfacial adsorption of the dye ions was occurred. This resulted in a decrease in absorbance of an aqueous phase. The interfacial adsorptivity of the dye ions increased with an increase in their hydrophobicity. In the presence of both a cationic and an anionic dye, an ion associate formed was extracted into an organic phase, and when stirred vigorously, a decrease in absorbance was observed in an aqueous and an organic phase. The interfacial adsorptivity of the ion associate decreased with an increase in its hydrophobicity. Ion association constants at the interface were of the order of 10⁶ dm³ mol^-1, and decreased with an increase in carbon numbers of the dialkylamino group of the cationic and anionic azo dye.