L-arginine-based natural deep eutectic solvent for destabilization and separation of stable colloidal dispersions: COSMO-RS evaluation with experimental study

The destabilization of stable colloidal dispersions remains a critical challenge in water treatment due to high electrostatic stability and fine particle size. In this study, a natural deep eutectic solvent (NADES) was synthesized and evaluated as a green coagulant. Fourteen candidates for NADES were screened first on the United States Environmental Protection Agency's (EPA) approval for safe discharge, and then the Conductor-like Screening Model for Real Solvents (COSMO-RS) predictions of stable formation below Atlantic Ocean subsurface temperatures while maintaining NADES structure fully immersed in a body of water. This two-step process identified a single optimal formulation, L-arginine and glycerol in a 1:6 M ratio. COSMO-RS molecular modeling was employed to optimize hydrogen bonding interactions and predict favorable thermodynamic behavior. Experimentally, Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of new hydrogen-bonded networks, and rheological measurements indicated an increase in viscosity, supporting enhanced molecular interactions in the NADES. Experimental performance of NADES and stable bentonite particles was assessed through zeta potential measurements, turbidity reduction, total suspended solids (TSS) removal, and floc size distribution under acidic, neutral, and basic pH conditions across a range of NADES concentrations. Results demonstrated that the NADES effectively neutralized surface charges of bentonite, induced flocculation, and significantly reduced turbidity, with optimal performance observed at 10 g/L across the tested pH ranges. Zeta potential measurements revealed pH-dependent surface charge modulation, confirming the role of electrostatic screening and hydrogen bonding in aggregation. Virtual models for property Evaluation of chemicals within a Global Architecture-Quantitative Structure-Activity Relationship (VEGA QSAR) modeling further validated the NADES components as low-toxicity and biodegradable, underscoring their environmental compatibility. This integrated computational and experimental investigation confirms L-arginine:glycerol NADES as a biodegradable, non-toxic, and highly efficient coagulant for destabilizing bentonite suspensions in saline environments.