Reformulating Bulk Liquid Membrane Using Deep Eutectic Solvent as Membrane Phase for Zn(II) Ions Removal From Aqueous Solution

Conventionally, bulk liquid membranes (BLM) utilize hazardous chemicals as the carrier and diluent to prepare the membrane phase. This study presents a greener alternative by formulating BLM with a deep eutectic solvent (DES) as the membrane phase, thereby eliminating the need for separate chemicals as carrier and diluent. Cetyltrimethylammonium bromide (CTAB) and oleic acid (OA) were used as the hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD), respectively. This study identified the suitable HBA:HBD ratio for DES synthesis, characterized its physicochemical properties and extraction equilibria and evaluated the DES performance as the membrane phase in BLM. In this study, the HBA:HBD ratio was varied from 1:30 to 1:80. Fourier transform infrared spectroscopy and thermogravimetric analyses confirmed the formation of DES between CTAB and OA. Meanwhile, the extraction equilibria demonstrated the extraction capability of DES and confirmed the stoichiometry of Zn(II) ions extraction. The equilibrium constant was found to be 0.7167 and the stoichiometric ratio of 1:1 between DES and Zn ion. Finally, the maximum Zn(II) ions removal efficiency (89.30%) was achieved at an HBA:HBD ratio of 1:40 DES as the membrane phase. The results were obtained under conditions where the stirring speed, temperature and operation time were 300 rpm, 60°C and 240 min, respectively.