Liquification of 2,2,4-trimethyl-1,3-pentanediol into hydrophobic eutectic mixtures: A multi-criteria design for eco-efficient boron recovery

[Display omitted] •Novel hydrophobic DES were developed by liquifying 2,2,4-trimethyl-1,3-pentanediol.•Comprehensive bottom-up approach was used to develop, characterize and optimize DES.•The DES properties vis-à-vis performance trade-off was thoroughly studied.•Exceptional selectivity and extraction efficiency (~98%) for boric acid was observed. New genres of ionic liquids and deep eutectic solvents (DES) have recently emerged as eco-efficient “designer’s solvents”. Herein, we report the liquification of the water soluble diol 2,2,4-trimehtyl-1,3-pentanediol (TMPD) into a novel hydrophobic DES with thymol or menthol, where the intrinsic supercooling properties of the constituents yielded eutectic mixtures with a wide liquid window and superior capabilities for boron extraction. The design framework of the TMPD-based DESs considered multiple criteria in which the trade-offs between the solvents’ properties, its boron extraction efficiency and leachability to the aqueous phase were thoroughly mapped. Formation of stable TMPD-boric acid complexes provided exceptional selectivity towards boron extraction from a synthetic brine solution. The performance of TMPD-based DESs was verified over various extraction parameters, with a single-stage extraction efficiency of ~ 98%, sustained stability over a wide pH range (2 – 8) and reusability over multiple regeneration cycle. This remarkable performance of the newly developed DESs associate the role of the TMPD as both a DES constituent and an active boron extractant, which disregards the use of hazardous organic diluents.