MOFs meet macropores: Dynamic direct crystallization of the microporous aluminum isophthalate CAU-10 on reticulated open-cellular alumina foams

• Published in: Microporous and mesoporous materials 2018-07, Vol.265, p.43-56
• Main Authors: Betke, Ulf, Klaus, Michael, Eggebrecht, Jakob G., Scheffler, Michael, Lieb, Alexandra
• Format: Article
• Language: English
• Subjects: Adsorption driven heat pump; Ceramic foam; Composite material; Dynamic direct crystallization; Metal organic framework
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2018.01.020

The direct crystallization of the microporous aluminum isophthalate CAU-10 onto macroporous alumina foams under dynamic conditions, i. e. a rotation of the autoclave, is studied. The cell size of the cellular supports is varied at a constant level of porosity and the resulting ceramic foams are characterized with respect to their morphology by means of X-ray computed tomography. The influence of the process parameters “autoclave rotational speed” and “support cell size” is studied together with the effect of a strut silanization prior to the coating procedure. The amount of deposited CAU-10 is essentially controlled by the specific surface area of the support, which increases for a decreasing cell size; a MOF loading of up to 46 wt% (dry) can be reached. The purity of the crystallized microporous material and its water uptake capacity depend on an effective flow of the synthesis gel inside the foam pore space, which is itself a complex function of the autoclave rotational speed and the cell size of the support foam. Optimal coating parameters with respect to the water adsorption performance of the entire micro-macroporous composite are identified, which result in a water uptake of up to 0.14 g·(gcomp.)−1. This equals 0.09 g cm−3 and represents a maximum heat of evaporation of 57 kWh·m−3 which is utilizable in a cooling application performing within a humidity range of 0%–75% r. h. The actual climatization power depends on the final realistic process parameters and may be lower. For heat pumping, the adsorption energy, as released by the adhesion of the H2O molecules on the walls of the MOF micropores, can also be exploited resulting in a ∼25% benefit for the maximal heat transformation performance. [Display omitted] •Dynamic direct crystallization of CAU-10 on open-porous cellular ceramics is shown.•Influence of agitation speed, foam cell size and surface chemistry on coating is studied.•Composites are characterized w.r.t. to deposited MOF mass and water uptake behavior.•Optimal process parameters w.r.t. to composite water uptake capacity are identified.