Superior Ion Adsorption of Polyelectrolyte Threaded Metal Organic Frameworks

Abstract

The high porosity, high surface area, uniform and ordered structure of metal organic frameworks (MOFs) are explored for selective ion adsorption. We report new composites of polyelectrolytes synthesized within the MOF porous MOF by extending the concept of “in situ polymerization in MOF” developed by Kitagawa and co-workers.[1] Sodium poly(4-styrene sulfonate) threaded in MIL-101 denoted as NaPSS~MIL-101 is synthesized directly with polymerization in situ of the MOF. The polyelectrolyte threaded NaPSS~MIL-101 exhibits superior exchange kinetics, high selectivity with co-ion rejection, reversibility, and durability. The ion adsorption kinetics is compared to commercial ion-exchange resin IR-120. The NaPSS~MIL-101 polyelectrolyte threaded in MOF has high surface area of 1850 m2/g and a large specific volume 0.85 mL/g. The fixed charges of the polyelectrolyte are exposed for full interaction with solvated ions and solvent, without the need of swelling as in conventional ion-exchange materials IR-120. Excellent selectivity based on charge is demonstrated when NaPSS~MIL-101 is immersed into a solution of two organic dyes. The anionic Acid Blue 9 is excluded though it has significant van der Waals affinity to high surface porous materials. Another example of polyelectrolyte synthesized in MOF is demonstrated by anionic polyvinyl benzyl trimethylammonium hydroxide (PVBTAH) threaded in ZIF-8 (PVBTAH~ZIF-8). The new composite materials is synthesized in steps of chloro-monomer impregnation, in situ polymerization, amination, and alkaline ion exchange.[3] The synthesized non-cross-linked PVBTAH~ZIF-8 material also exhibits superior ion-exchange kinetics compared to conventional ion-exchange resins.[3] References: [1] T.Uemura, K.Kitagawa, S. Horike, T. Kawamura, S. Kitagawa, M. Mizuno, and K. Endo, Chem. Commun. 48 (2005) 5968-70. [2] Liang Gao, Chi-Ying Vanessa Li, and Kwong-Yu Chan, Chem. Mater. 27(10) (2015) 3601-3608. [3] L. Gao, C.Y. V. Li, K.Y. Chan, and Z.N. Chen, J. Am. Chem. Soc. 136 (2014) 7209-7212.