A highly selective green supported liquid membrane by using a hydrophobic deep eutectic solvent for carrier-less transport of silver ions

Abstract

A new supported liquid membrane (SLM) was designed by using a suitable deep eutectic solvent (DES) as the hydrophobic liquid membrane phase for the selective and facilitated carrier-less transport of Ag⁺ ions. The deep eutectic solvent was composed of a 4/1 molar ratio of L-menthol/salicylic acid and was impregnated into a microporous polypropylene membrane to prepare a novel carrier-less SLM system. The highly selective facilitated transport of silver ions was accomplished by using sodium thiosulfate as a highly selective stripping agent for Ag⁺ ions in the aqueous strip phase (SP). Some important factors, including the concentration of picric acid in the feed phase (FP), pH of the two aqueous phases, stirring rate, transport time, and nature and concentration of the stripping agent were also investigated and optimized. In the presence of 2.8 × 10⁻² mol L⁻¹ picrate ions as an appropriate ion pairing agent in the FP and 0.025 mol L⁻¹ thiosulfate as a convenient metal ion acceptor in the SP, the amount of Ag⁺ ion transport found to occur almost quantitatively after 60 min is 90%. Compared with other SLM systems reported in the literature, the designed DES–SLM system exhibited suitable permeability and higher selectivity for Ag⁺ ion transport from aqueous solutions containing Fe²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Pb²⁺, and Cd²⁺ as competing metal ions.