The thus-shaped objects were found to exhibit XRD patterns similar to a MOF-5 degraded by humidity. This was attributed to the formulation procedure prior to printing rather than to the printing procedure itself. Nevertheless, these 3D printed objects were shown to have the ability to adsorb H 2 despite the complex polymer environment. Typically, MOFs are produced in polycrystalline powder form, with the size of individual crystals ranging from several tens of nanometers to a few microns. Continuous studies on synthesis optimization and product characterization have stimulated the production of MOFs on a larger scale. Thus, a number of them are now commercially available and provided by BASF (HKUST-1/Basolite C300, ZIF-8/Basolite Z1200, Fe-BTC/Basolite F300), Strem Chemicals (CAU-10, MIL-53(Al), MIL-101(Al), PCN-250(Fe), UiO-66), and others. Fig. 1 Schematic representation of the pelletization process applied to polycrystalline MOF powder. V. Finsy, H. Verelst, L. Alaerts, D. E. De Vos, P. A. Jacobs, G. V. Baron and J. F. M. Denayer, Pore-Filling-Dependent Selectivity Effects in the Vapor-Phase Separation of Xylene Isomers on the Metal−Organic Framework MIL-47, J. Am. Chem. Soc., 2008, 130, 7110–7118, DOI: 10.1021/ja800686c.

Under the same conditions, the UiO-66 framework proved to be more stable toward high pressures. 47 Upon compression up to 69 MPa, the BET surface area of the pellet reached 1080 m 2 g −1, which is identical to that of the parent powder. Therefore, when tested for octane adsorption, the UiO-66 pellet compressed at ∼69 MPa demonstrated a saturation loading comparable to its powder counterpart (2.1 vs. 2.5 mmol g −1, respectively).Though the hospitality industry is just one of many sectors participating in the MOF competition, the chef and pastry chef categories have become more widely publicized in recent years. MOF chefs wear have the designation emblazoned on their chef coats via a tri-colored collar and the MOF logo, serving as a very visible representation of the fact that they've achieved a fantastically high level of excellence. If you see a date below the MOF logo, that's the year he or she won the MOF title. For MOFs, the primary goal of using binders is to enhance the mechanical stability of the granules. For this purpose, compounds capable of creating decently strong bonds with the surfaces of MOFs are preferred as binders. As an example, this implies cohesion of MOF particles via hydrogen bonding, and therefore, compounds possessing multiple functional groups (mainly –OH) are beneficial. This includes alcohols (polyvinyl), sugars (sucrose, cellulose), esters (hydroxypropyl cellulose) and others. However, upon shaping they cannot be removed due to the limited thermal stability of MOFs.

As with granulation, extrusion implies the addition of binders to ensure sufficient mechanical strength to extrudates by developing cross-linking forces between the individual particles. Therefore, the choice of binder and its content are governed by the same principles as in the case of granulation and pelletization. Namely, the binder should provide sufficient mechanical stability with the minimum loss of intrinsic physical and chemical properties of the parent powder. Thus, zeolites extruded with clays and boehmite as binders and cellulose-based plasticizers experienced certain alterations of textural and chemical properties as well as a clear enhancement of mechanical resistance. 77 Recently, 3D printing has been applied to a large number of structured adsorbents and catalysts. Thus, Al 2O 3 was shown to be printable into monoliths exhibiting high catalytic efficiency as well as good recyclability. 95 Zeolites 13X and 5A have also been printed into monoliths for CO 2 removal purposes, 96 while a 3D-printed zeolite (ZSM-5) has been probed for CO 2, CH 4 and N 2 separation. Among the other printed structures can be found carbons, 97 amorphous aluminosilicates 98 and other classes of adsorbents. 99 Q. Wang and D. Astruc, State of the Art and Prospects in Metal−Organic Framework (MOF) – Based and MOF-Derived Nanocatalysis, Chem. Rev., 2020, 120, 1438–1511, DOI: 10.1021/acs.chemrev.9b00223.Technically, any French citizen 23 years or older who pays the 60-euro entrance fee can compete, but few have the preparation and dedication necessary to make a serious bid for the title. A particularity of the competition is the absence of podium. Indeed, the MOF title is awarded based on the average marks obtained in the tests, so there may well be several winners or none, if no one has reached the required score to become a laureate. Fig. 6 Schematic representation of the extrusion process on a piston-type extruder (a) and on a single screw-type extruder (b). In 2014, Grande et al. 82 performed a study on the manual extrusion of Co-based UTSA-16 with emphasis on the paste composition. To form the paste, they combined polyvinyl alcohol as the binder and a water/propanol (1/1) mixture as the plasticizer. The paste was further extruded into strips using a syringe of a chosen diameter. The thus-shaped MOFs were then dried at 80 °C for 12 h. When varying the binder content, no significant loss in specific surface area with 2 wt% binder was observed. A further increase to 3 wt% PVA led to a 5% loss of SSA. Notably, the authors stated that an activation temperature lower than 120 °C was insufficient to remove the water/propanol mixture. At the same time, 2 wt% binder was found to be adequate to provide a decent crushing strength of around 20 N upon conventional compression tests, comparable to commercial zeolite 4A extrudates (12 N). For comparison, the absence of a binder resulted in a lower mechanical strength of around 7 N. Dhainaut et al. 49 reported a detailed study of the effect of compression on the textural properties of some of the most studied MOFs including UiO-66, UiO-66-NH 2 and UiO-67. They found that the impact of pressing UiO-66 and UiO-66-NH 2 was in line with the pressure applied as their textural properties decreased accordingly. Thus, they reported a 26% decrease in UiO-66-NH 2 BET surface area upon compression at 164 MPa, which is in good agreement with the results reported by Peterson et al. 51 Interestingly, it was found that the UiO-67 structure started collapsing upon compression above 63 MPa, while at 82 MPa it lost ∼80% of its initial surface area (2034 vs. 397 m 2 g −1). Based on their results, they proposed to limit the compression to a final bulk density that represents at most 80% of the crystal density of the related MOF. Lately, Grande et al. applied 3D-printed UTSA-16 solids for selective CO 2 capture. 118 For the binding system, they used a mixture of boehmite and hydroxypropyl cellulose, representing 36 wt% of the final dry solid content. Interestingly, the presence of boehmite might provide some Lewis acidity, which was not probed. The as-obtained solids with a diameter of 28 mm presented a woodpile structure with only little sagging in the middle. After activation, the S BET reached 540 m 2 g −1, which is higher than expected as UTSA-16 powder typically presents a S BET of 630 m 2 g −1. While the solids retained selectively CO 2 over N 2, the additional presence of water molecules desorbed the CO 2 molecules.

Extrusion is another classical technique which is especially used to produce extrudates and honeycombs for catalytic converters. When it is applied to MOFs, limited impact on the structural and textural properties can be observed for most MOFs, due to lower pressures and shear forces applied. Extrusion requires, however, finely controlling the formulation and related rheological properties of the extruded paste. Advantageously, extrusion can also be used for the direct preparation of MOF objects starting from precursors (reactive extrusion). The latter is of particular interest as it allows limiting or avoiding completely the toxic solvents traditionally used for the synthesis of MOF powders. At the same time, reactive extrusion implies a continuous process with high potential space time yields. While this approach might not be applicable to all MOF structures, the reactive extrusion presents several advantages over more conventional methods such as solvo/hydrothermal or microwave-assisted syntheses of MOFs. On the other hand, these conventional methods remain better in terms of obtained crystallinity and surface area for most MOF structures.Some of the most celebrated and respected chefs and hospitality professionals in the world are MOF winners. But with great recognition comes great responsibility: each MOF is expected to further their profession and guide the next generation of craftsmen in their search of not only excellence but also innovation. They're also tasked with continually expanding their own professional repertoire, learning new techniques and bettering themselves despite the accolades they've already collected. For instance, the authors used copper hydroxide and trimesic acid mixed with methanol as a feed material to produce HKUST-1. Upon extrusion at room temperature, the product was washed with ethanol and dried to yield HKUST-1 extrudates with a specific surface area of 1738 m 2 g −1 and a crystal structure expected for this MOF. Furthermore, the authors showed that ZIF-8 extrudates can be made by both single and twin screw extrusion processes. For this, they used a blend of zinc carbonate and 2-methylimidazole with no solvent added and extruded it at 200 °C. In both cases, the processes yielded a crystalline product with the ZIF-8 topology and high surface areas: 1604 m 2 g −1 (twin screw) and 1750 m 2 g −1 (single screw). Lastly, the authors produced a highly crystalline Al-fumarate with a BET surface area of 1010 m 2 g −1 by extruding a mixture of Al-sulfate, fumaric acid and sodium hydroxide at 150 °C. It is worth noting that this approach enables the production of MOFs with decent space-time yields (STY) as single and twin screw extrusions are continuous processes.