Highly-Efficient adsorptive separation of Cs+ from aqueous solutions by porous polyimide membrane containing Dibenzo-18-Crown-6

Abstract

To develop recyclable adsorptive materials for high-efficient separation of cesium (Cs+) from aqueous salt lake brine is of great significance. Herein, a novel polyimide (PI-18C6) with high molecular weight (Mn = 93 kDa) and high thermal stability (Td > 380 °C) was synthesized by the condensation and polymerization of di(aminobenzo)-18-crown-6 (DAB18C6) and 4,4′- (hexafluoro-isopropylidene) diphthalic anhydride. Simultaneously, porous membranes for Cs+ selective adsorption were prepared by non-solvent induced phase separation (NIPs) method. Results suggested that the adsorption of Cs+ on PI-18C6 membrane is the monolayer chemical adsorption as confirmed by fitting its adsorption data using pseudo-second-order adsorption model and Langmuir isotherm model, respectively. PI-18C6 membranes displayed a high adsorption capacity up to 54.08 mg g−1 combined with a higher selectivity of coexisting ions such as K+, Na+, Mg2+ and Rb+. Theoretical calculation results showed that the PI-18C6 has a higher adsorption energy for Cs+ (-395.72 kJ mol−1) than K+ and Rb+. The significant higher adsorption energy at the crown-ether sites is largely attributed to the fact that the cavity diameter cavity of DB18C6 (2.6–3.2 Å) is a closer to Cs+ (3.34 Å). The membrane also exhibited excellent repeatability. In summary, our study paves a facile way to develop functional membrane materials for the selective adsorption separation of Cs+ from aqueous solution.