Cellulose-MOF suspensions: towards self-supported polyfunctional materials designed from ultrafiltration
Résumé
Metal-organic frameworks (MOFs) are promising materials to address critical issues such as petrochemical and gas separation, filtration, catalysis, sensing and energy storage. Large-scale deployment of MOFs is however hampered by their crystalline powder state, which results in poor processability. Recently, the hybridization of MOFs with biopolymers has emerged as a greener, biocompatible strategy with improved processability into membranes, films, and porous materials. Nevertheless, the physiochemical properties of the biopolymer-MOF mixtures, and their relationship to the composite structure and functionality, need to be investigated to promote their use in real applications. The present work focuses on the preparation of thin nanocomposites from commercial ZIF-8 (a synthetic zeolite) and cellulose nanocrystals (CNCs) aqueous suspensions using membrane ultrafiltration. An investigation carried out with a rheo-optical setup show that the addition of small quantities of CNCs (1:20 CNC:ZIF-8 vol. ratio) affect significantly the flow of ZIF-8 particles, endowing the suspension with colloidal stability through the electrostatic interactions between the two materials. The CNCs removed the yield stress observed in the ZIF-8 suspensions, prevent their aggregation into a percolated network, and enabled their deposition on the membrane during filtration. The process was also investigated with in situ SAXS, which tracked the concentration of CNCs along the deposit height. Here, the deposit was formed by layers of CNCs containing ZIF-8 particles, perpendicular to the membrane. Finally, the porosity of ZIF-8 to water was tested with a custom-made porosimeter, showing that the adsorbed CNCs did not affect the intrusion/extrusion pressure, or the available pore volume in the hybrid material.