(277a) Bridging the Interfacial Gap in Mixed-Matrix Membranes for Precise Molecular Sieving in Organic Solvents

Organic solvent separations based on membrane technology offer a lower energy alternative compared to traditional thermal separations. However, it requires materials that operate reliably in chemically aggressive environments. To obtain solvent-resistant membranes, crosslinking is commonly required, usually by immersing membranes in a solution of reactive crosslinking agents. In quest to achieve highly selective membranes, we investigated the mixed matrix membranes (MMMs) containing metal–organic framework (MOF) fillers, owing to the regularity and ordered pore arrangement in the MOF structure [1]. However, the poor interfacial adhesion between the polymer matrix and the MOF filler has emerged as a bottleneck, creating defects and random voids on the membrane’s surface. In this study, we bridged the gap between their material constituents. We prepared a series of novel membranes comprising MOF nanoparticles with similar chemical and morphological properties but having various pore sizes (UiO-66–68-NH₂). The MOFs’ surfaces were covalently grafted with poly(N-isopropylacrylamide) (PNIPAM) chains, which could then become entangled with the membranes’ polymer matrix. This strategy was inspired by the natural phenomenon of strong interfacial adhesion between the calcified cementum of the tooth and the surrounding tissues provided by intermingled collagen fibers. Morphological investigations and organic solvent nanofiltration (OSN) tests revealed that membranes with PNIPAM-grafted fillers do not suffer from the formation of pinholes at the filler–matrix interface that are detrimental to the filtration performance. The experimental results showed an excellent match with a predictive model of nanofiltration built around the premise of liquid transport through the highly ordered pores of the MOF filler. The OSN test revealed the increase in the flux and molecular weight cut-off values with increasing MOF aperture size which confirm the key role that internal MOF pores play in the filtration.

[1] L. Cseri et al., J. Mater. Chem. A, 2021, 9, 23793–23801.