Poly(styrene-co-4-hydroxystyrene) nanofiber membrane for highly selective and efficient Rb plus capture from high salinity solution

Highly selective and efficient rubidium ion (Rb+) capture from high salinity aqueous solutions has always been an extremely challenging task. Herein, a novel Rb+ selective adsorption nanofiber membranes are fabricated via electrospun by using a linear polymer poly(styrene-co-4-hydroxylstyrene) (P(S-co-VPh)) containing phenolic hydroxyl groups, which hydrolyzed from the copolymer of styrene (St) and 4-acetoxystyrene (AS). GPC, 1H NMR and FTIR, results showing that the polymer chain structures can be effectively regulated via changing the monomers ratio. After electrospinning, the morphologies and specific surface areas of as-prepared membranes are evaluated by FESEM and BET. The adsorption experiment results show that Rb+ adsorption capacity gradually increase with phenolic hydroxyl group density of the membrane surfaces. The adsorption process agrees with the Langmuir model, and the maximum adsorption capacity (qm) is up to 53.15 mg/g, and the adsorption kinetics obeys preferentially the pseudo-second-order kinetics. Intraparticle diffusion model shows that the adsorption is a multi-step limiting process and breakthrough curve is best fitted by the Yan model. Surprising, over 80% of the maximum adsorption capacity can be achieved within 15 min, and adsorption equilibrium is reached within 1.0 h. Furthermore, the excellent selectivity coefficient K of Rb+/Mn+ in high salinity binary mixtures are 580.2, 426.4, 258.1 and 128.3 for Na+ (9.6 g/L), Mg2+ (1.28 g/L), Ca2+ (0.4 g/L), K+ (0.5 g/L) used as the interfering ions, respectively. Moreover, the recovery rate remains exceeding 85% after five adsorption-desorption cycles, indicating that nanofiber membranes prepared by P(S-co-VPh) have significant application potential for rubidium separation and purification in the future.