Insights into application of aqueous biphasic systems of deep eutectic solvents composed of benzyltrialkylammonium chloride in dye separation

Abstract

Deep eutectic solvents (DES) are considered the newest entry in the list of green solvents and they are analogues of ionic liquids (ILs), with excellent solvent characteristics better than commonly used organic solvents and ILs. Owing to this, We have prepared DES using benzyltrialkylammonium chloride (BTAAC) including benzyltrimethylammonium chloride (BTMAC), benzyltriethylammonium chloride (BTEAC), and benzyltributylammonium chloride (BTBAC) as hydrogen bond acceptors (HBA) and glycols, like ethylene glycol (EG), diethylene glycol (DEG) and triethylene glycol (TEG) as hydrogen bond donors (HBD). Aqueous biphasic systems (ABS) were developed using the synthesized DESs and K3PO4, K2HPO4, and K2CO3 at 298.15 K and atmospheric pressure. The phase-forming ability of DES has been evaluated based on the nature of potassium salts, HBA and HBD. In most cases, the influence of salts on ABS formation was found to follow the order: K3PO4 > K2HPO4 > K2CO3, while HBAs follow: BTBAC > BTEAC > BTMAC. The performance of the ABSs was experimentally applied for the extraction of Methyl orange (MO), Eriochrome black T (EBT), and Eosin Y (EY). In most ABS, the extraction order for the studied dyes noticed was: MO < EBT < EY, consistent with their hydrophobic nature. ABS consisting of BTBAC:TEG + K2HPO4 and BTBAC:TEG + K3PO4 was found to lead to the complete extraction of MO, EBT, and EY. The recovery of extracted EY dye was performed by adsorption method using starch-modified chitosan as an adsrobent.