Abstract
This manuscript provides insights into the solubilization of two direct dyes, direct green 6 (DG-6) and direct yellow 44 (DY-44), in different surfactant systems. It reports the interaction and applicability of surfactants to elevate the solubility of direct dyes in aqueous medium. Different combinations of cationic (cetyltrimethylammonium bromide) and nonionic surfactants (Triton X-100, Tween-20) have been employed for said purpose. Inclusion of nonionic surfactants to micellar media of ionic ones enhances space within micelle to accommodate more solubilizate within it. Conductometric and spectroscopic measurements were applied for investigating the interaction of dyes in these surfactant solutions. The properties of surfactants, their behavior in aqueous systems, and thermodynamics have been evaluated in terms of critical micelle concentration (CMC), and change in Gibbs energy (ΔGm), enthalpy (ΔHm), and entropy (ΔSm) of micellization. While the solubilization capability of different surfactant systems was explored with the help of binding (ΔKb) and partition (ΔKx) parameters. Moreover, the stability of the process has been revealed by calculating the Gibbs energies of binding (ΔGb) and partition (ΔGp). The results revealed that mixed surfactants are more suitable agents for the solubilization of dyes. It was also observed that the partition of dye molecules is greatly dependent on their interaction with the surfactant molecules. This study will provide the basis for choosing the suitable surfactant system to be used in various surfactant-based dye removal techniques.
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•Cationic surfactant CTAB has a great ability to solubilize direct dyes in the aqueous system.•The addition of non-ionic surfactants in the cationic surfactant system induces synergism.•The binding and partition of dyes in different surfactant systems are greatly dependent on their structure.•The solubilization of direct dyes in single and mixed surfactant systems is spontaneous.