Development of mt-NADES Beads and Optimization for Efficient Extraction of Methylene Blue Using Response Surface Method.

The escalating contamination of aquatic environments by synthetic dyes, particularly methylene blue (MB), represents a pressing environmental challenge, with far-reaching implications for ecosystem health and human welfare. Technologies such as adsorbents have been shown to be promising remediation technologies. Here, we report on the development of biopolymeric adsorbent beads by functionalizing alginate-chitosan matrices with menthol-thymol-based natural deep eutectic solvents (mt-NADES), demonstrating notable MB removal capacity. The strategic incorporation of NADES simultaneously enhances hydrophobic interactions and structural integrity, yielding superior dye adsorption toward the matrix. Response surface methodology (RSM) established an optimal operational parameter (275 ppm MB, 155 mg adsorbent, pH 10, 150 min contact time), achieving a maximum MB removal of 95.21%, remarkably concordant with the predicted value of 97.41%, showcasing strong model prediction. Kinetic analysis demonstrates pseudo-second-order adsorption behavior, while isotherm modeling confirms multilayer adsorption on heterogeneous active sites (Freundlich model), with thermodynamic parameters confirming spontaneous, endothermic adsorption characteristics. Remarkably, the mt-NADES beads demonstrated outstanding reusability, retaining >95% removal efficiency across six consecutive cycles, underscoring their practical viability. These NADES-functionalized biopolymeric beads provide a sustainable treatment approach for critical industrial wastewater needs while advancing the green chemistry principles.