Hydrophobic deep eutectic solvents for highly efficient n-hexane capture

A green HDES based on Bet and C 10 was synthesized for n -hexane capture. • Increasing C 10 ratio lowed viscosity and density, and increased free volume and hydrophobicity of Bet:C 10 HDES. • The optimized Bet:C 10 (1:16) HDES exhibits a partition coefficient ( K ) of 0.0046, outperforming silicone oil by 18%. • n -Hexane absorption is a spontaneous and enthalpy-driven physical process. • Bet:C 10 HDES demonstrates excellent reusability, retaining >99% capacity over 10 absorption-desorption cycles. n -Hexane is a hazardous hydrophobic volatile organic compound (VOC) posing significant neurotoxic and environmental risks. While liquid absorption is a standard elimination strategy, traditional solvents suffer from high volatility and energy-intensive regeneration. In this work, a novel class of hydrophobic deep eutectic solvents (HDESs) composed of natural betaine (Bet) and decanoic acid (C 10 ) was developed for efficient n -hexane capture. Physicochemical characterization manifested that Bet:C 10 HDESs are highly thermal stable, along with relatively low viscosity (17.5-37.6 mPa·s) and density (0.8979-0.9213 g/cm 3 ) at 30 °C, enabling them as suitable absorbents. Increasing C 10 ratio reduced the viscosity and density, enhanced the hydrophobicity and enlarged the molar free volume of Bet:C 10 HDESs. These physicochemical changes significantly improve affinity for n -hexane. Consequently, the optimized Bet:C 10 (1:16) HDES achieved a vapor-liquid partition coefficient ( K ) of 0.0046 at 30°C, demonstrating an absorption performance 18 % superior to traditional silicone oil. Thermodynamic analysis confirmed the absorption is a spontaneous, enthalpy-driven process ( ΔH < 0, ΔG < 0). 1 H NMR and ATR-FTIR spectra and Spearman correlation coefficients analyses confirmed that the interaction is governed by physical forces. Furthermore, the HDES exhibited outstanding reusability, retaining >99 % of its absorption capacity after 10 consecutive cycles. These findings establish Bet:C 10 HDESs as promising and green alternatives for industrial n -hexane capture. Download: Download high-res image (149KB) Download: Download full-size image