A comprehensive spectral study of dye-surfactant complex formation by Xylenol Orange with selective aqueous micellar media of CPC, rhamnolipids and saponin

Abstract This study investigates the novel interaction dynamics between the biosurfactant rhamnolipids, saponin (reetha or sapindus saponin), and the conventional surfactant cetylpyridinium chloride (CPC) with the anionic organic dye, Xylenol Orange (XO), in aqueous micellar media. Absorption spectroscopy revealed the strong interactions between XO and CPC, especially in the premicellar concentration range. The formation constants for the dye-surfactant complexes were calculated, shedding light on the nature and strength of these interactions. A comprehensive analysis using DLS, SEM, zeta potential measurements and surface tension experiments further confirmed the complexation, with CPC exhibiting robust electrostatic interactions with XO, as indicated by notable changes in hydrodynamic size and surface morphology. In contrast, saponin exhibited much weaker interactions with XO, as evidenced by minimal spectral shifts and slight increases in hydrodynamic size. Rhamnolipids, which exhibited intermediate interactions, formed weaker complexes than CPC, but stronger than saponin. The study clearly demonstrates that CPC-XO interactions are the most efficient for complex formation, positioning CPC as the optimal choice for applications targeting XO removal from aqueous solutions. This research significantly contributes to the development of sustainable surfactant-based solutions for environmental management and highlights CPC as a key player in the extraction and removal of dyes from contaminated water.