Hierarchical Porosity in MOFs : processing, and structuration for improved sorption properties. – HP-MOFs

Commercial macro/mesoporous alumina membranes are used as substrates. MOF/alumina composites are easily obtained through reagent filtration through the membrane channels, following a dynamic step-by-step methodology.

- an original synthetic methodology allowing the composite preparation has been developped
- experimental parameters governing the composites formation have been explored and identified
- composites showing high MOF loadings have been obtained
-sorption properties of these composites have been studied.

The prepared microporous molecular materials are protected by the inorganic shell. Resulting composites are easy to handle objects. They show promise for potential use in devices dedicated to supported catalysis and/or sensing applications.

Crystal Growth & Design 2011, 12, 5424-5433.

Owing to their potential applications ranging from catalysis to gas storage, porous coordination polymers (or MOFs, for Metal-Organic Frameworks) have received considerable attention along the last few years. While they constitute a class of promising materials, they show several drawbacks related to their rather small pore sizes (less than 2 nm, microporous regime), mechanical fragility (obtained as crystals) and to the difficulty to structure and/or to shape them for their use in targeted applications. So far, only very few work has dealed with these different aspects.
HP-MOFs objective is threefold:
i) To elaborate MOF-tubes from inner walls of porous inorganic templates, in order to embed the MOF in a protecting inorganic shell, with improved mecanichal properties compared to crystals, and facilitate their use and handling.
ii) To remove the template to recover the corresponding free MOF-tubes;
iii) Finally, to evaluate the sorption properties of this new class of porous objects relative to the ones of bulk MOFs. Since both inner and outer MOF-tube walls will contribute to exchanges with external media, these tubes will present improved sorption properties.
HP-MOFs will be implemented in three well defined and complementary scientific tasks in agreement with its objectives. After a rapid MOF screening to determine the best candidates, the methodology envisioned to design MOFs with bimodal porosities will be validated demonstrating: first, the possibility to grow highly oriented MOFs films inside the pores of commercial porous alumina templates; and second, that the inorganic template could be removed through chemical treatment without destroying the metal organic framework. Then, highly regular meso-structured alumina membranes will be used in order to access to monodisperse tubular MOFs with control over their length and diameters (external and internal). Finally, benefits of the MOF structuration towards CO2 sorption will be investigated in detail through an accurate comparison of sorption properties between the new structured materials and their parent MOFs (i.e., as-synthesized bulk materials and/or shaped as MOF nanoparticles).
HP-MOFs is organized around two young assistant professors belonging to the Laboratoire de Chimie de Coordination du CNRS (LCC-CNRS, Toulouse). Their expertise in molecular chemistry is directed to coordination polymer-based materials. The coordinator has several-year experience in MOF type systems and their processing on surfaces. The research team is completed by a collaboration with S. Brandes (ICMUB, Dijon) who has long experience in sorption investigation of porous solid (including MOFs). An important aspect of the project relies on highly-structured alumina membranes. These membranes will be provided by L. Arurault (CIRIMAT, Toulouse) who is mastering the preparation of anodic aluminum oxide membranes with controlled and adjustable pore sizes.