2, Ecole Normale Supérieure, Paris, , France
3, UPMC, Paris, , France
4, Université Paris Diderot, Paris, , France
5, Université Montpellier, Montpellier, , France
Membrane separation has emerged as a promising alternative to cryogenic distillation or amine-based wet scrubbing for the CO2 capture, with potentially high efficiency, lower energy consumption, ease of scale-up and environmental friendliness. However, these membranes typically derived from polymers suffer from an inherent trade-off between permeability and selectivity. To enhance their performance, composite membranes (or mixed matrix membrane, MMM) which consist of filler particles dispersed into an organic polymer phase were proposed since they potentially combine the gas transport and separation properties of the incorporated particles with the good processability and mechanical properties of the polymers. Metal Organic Frameworks (MOFs) were recently proposed as fillers since they present a high separation performance owing to their size/shape exclusion or selective adsorption of gas molecules. However, MOF-based MMMs still pose limitations, which are mainly related to the low MOF loading for numerous MMMs (< 30 wt%). While the permeability of such MOF-based MMMs is usually improved in comparison to pure polymer membranes, an improvement of selectivity is only rarely observed. This mainly results from the fact that the selectivity of this system is driven by the polymer matrix which is the dominant component. In addition, a possible physico-chemical mismatch between MOFs and polymers may lead to the aggregation of MOFs fillers in the polymer matrix and interphase defects (macro or nanovoids). Such voids provide new bypasses through the MMMs that reduce the separation efficiency and compromise performance. There is thus a need to design nanoparticles of MOFs with a good control of the surface chemistry and morphology (diameter and shape) for the shaping of MMMs.
This communication deals with the synthesis of microporous and water stable MOFs nanoparticles for the processing of MMMs. We focused mainly our attention on the aluminum trimesate MIL-96(Al) and the zeolitic imidazolate ZIF-8 which are attractive for the selective capture of CO2. The synthesis of MIL-96(Al) crystals of different morphology and diameter was achieved by using water as the main solvent. Monodisperse MIL-96(Al) nanoparticles were combined to polymers for the preparation of defect-free MMMs. The microstructure of MMMs and compatibility of MOFs nanoparticles within polymers were also investigated through a complete characterization of MOFs/polymer colloidal solutions by combining complementary experimental (DLS, SAXS, TEM, HAADF-STEM) and computational tools. This study has shown the influence of the surface chemistry of MOFs and the properties of polymers on the physico-chemical matching between MOFs and polymers.
 M. Benzaqui, R. Semino, N. Menguy, F. Carn, T. Kundu, J. M. Guigner, N. B. McKeown, K. J. Msayib, M. Carta, E. Malpass-Evans, C. LeGuillouzer, G. Clet, N. A. Ramsahye, C. Serre, G. Maurin, N. Steunou, ACS Appl. Mater Interfaces, 8, (2016), 27311-27321