Shaping of metal-organic frameworks into mechanically stable monoliths with poly(vinyl alcohol) by phase separation technique

Abstract

Abstract The metal-organic frameworks (MOFs) Basolite™ A520 (aluminum fumarate, Alfum) and MIL-101(Cr) were shaped into monoliths for the first time using a phase separation technique with the hydrophilic polymer poly(vinyl alcohol) (PVA). These composite materials (MOF@PVA) could be loaded with up to 80 wt% of MOF under retention of crystallinity (verified by powder X-ray diffractometry), porosities (from N2 and H2O adsorption) and morphology of MOF particles (verified by scanning electron microscopy). In the MOF@PVA monoliths, the mass-weighted apparent BET surface area from nitrogen sorption studies and the water vapor uptake capacity reproducibly reached 60–100% of the neat MOF values. Alfum@PVA composites with a MOF loading of 50–80 wt% show an increased quantitative porosity. A detailed pore analysis by the t-plot method indicates, however, that only 30–70% of the Alfum-micropore volume were retained during the used phase separation technique. The increased porosity is due to additional mesopores from interfacial voids which were formed between Alfum-particles and the PVA polymer. These additional pores lead to an increase in water capacity compared to the neat/pure MOF. While the neat PVA monoliths show a primarily plastic and elastic behavior, the monoliths with 50 and 65 wt% Alfum exhibit slightly plastic properties and a high resistance against deformation. Higher stresses (up to 0.12 N/m2, i.e. up to a force of 63 N) can be exerted together with a lower strain (