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In 2014 Ahmed et al. 156 proposed a different method for MOF shaping based on controlled freezing. According to it, a MOF powder in suspension can be shaped into monoliths upon controlled freezing of the solvent with its subsequent elimination via freeze-drying. The authors applied this methodology to obtain Cu-based HKUST-1 monoliths. For this, the MOF precursors were dissolved in DMSO and left for 24 h at 80 °C. After that, the solution was frozen in liquid nitrogen for 1 min and placed into a freeze-dryer to sublime the solvent. This procedure yielded highly crystalline HKUST-1 monoliths as confirmed by XRD. Moreover, the specific surface area was 870 m 2 g −1 with characteristics of both micropores and mesopores, as visible from the N 2 physisorption isotherms. Additionally, as shown by Hg intrusion, the monoliths exhibited macropores with diameters around 0.4 and 10 μm. Importantly, these macropores generated upon ice-templating were oriented in one particular direction due to the orientational growth of ice crystals during freezing. Lastly, the authors showed that the size of these macropores could be varied by altering the freezing temperature. Thus, upon freezing at 5 °C the macropores were two times bigger (∼50 μm) than the macropores generated upon freezing at −80 and −20 °C (32 and 25 μm, respectively). 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. Jérémy Dhainaut received his PhD in Chemistry of Materials from the University of Upper Alsace (Mulhouse) in 2012. He further developed an expertise in the fields of porous materials and their shaping through postdoc positions at the Ceramic Synthesis and Functionalisation Laboratory (Cavaillon), the Institute of Research on Catalysis and the Environment (Lyon), the Laboratory of Catalysis and Solid-State Chemistry (Villeneuve d’Ascq), and the Institute for Integrated Cell-Material Sciences (Kyoto). In 2019, he was appointed as a CNRS Researcher at UCCS. His work focuses on studying the effect of shaping methods on the physico-chemical properties of porous materials including MOFs.

Further reports on shaping ZIF-8 via DIW include the work by Lefevere et al., 112 who managed to formulate the MOF with a blend of inorganic and organic binders. The former was added to improve the mechanical stability of the shaped objects, and the latter to enhance the rheological properties of the paste. Typically, the parent ZIF-8 powder (66.7 wt%) was mixed with bentonite (16.7 wt%) and methylcellulose (16.7 wt%) with a subsequent addition of water and mixing to form a homogeneous printable paste. Once homogenized, it was further loaded into a 50 mL syringe and extruded through 250 and 600 μm diameter nozzles in a layer-by-layer fashion at room temperature ( Fig. 11g and h). X. Fang, B. Zong and S. Mao, Metal–Organic Framework-Based Sensors for Environmental Contaminant Sensing, Nano-Micro Lett., 2018, 10, 64, DOI: 10.1007/s40820-018-0218-0. Fig. 8 Comparison of the extruded 84 and pelletized 38 ZIF-8 (left); and the pelletized 47 and extruded 79 HKUST-1 (right). Numbers indicate the BET SSA upon shaping the pristine powder into extrudates and pellets. Ligand codes: BTC – benzene-1,3,5-tricarboxylic acid; BDC – benzene-1,4-dicarboxylic acid; FDC – 2,5-furandicarboxylic acid; TazBz – 3,3′,5,5′-azobenzenetetracarboxylate; and MIM – 2-methyl imidazole. Binder codes: PVA – polyvinyl alcohol; PVB – polyvinyl butyral; MRA – mesoporous ρ-alumina; and HPC – hydroxypropyl cellulose. “—” not specified.As is evident from Table 13, both extrusion and DIW can yield shaped objects while preserving the textural properties of pristine MOFs. The loss in surface area in the case of the 3D printed objects is somewhat higher than the binder content which is due to the presence of the plasticizer. The final printed objects have a developed network of millimeter-sized channels thanks to the layer-by-layer deposition upon printing. This can significantly improve the diffusion of gas or liquid within the shaped objects. Spray-drying The spray-drying technique has been known for over a century. As the name suggests, it is used to dry powder-like materials in a continuous fashion. Compared with ovens and conveyor belts, spray-dryers allow treating several tons per hour of wet product. Over the past few decades, the application potential of spray-drying has considerably expanded and now includes the food industry, 125 the pharmaceutical industry, 126 and many others. 127 The paste formulation is crucial and requires special attention. Indeed, mixing of the parent powder with a liquid should yield a paste with suitable rheological properties to enable extrusion. There are many aspects which define the flow behavior such as the size and shape of the powder particles, their chemical properties, etc. Overall, the paste viscosity is dictated by the liquid content and can be decreased upon increasing the total liquid/solid ratio. More viscous pastes might require higher pressures for displacement within an extruder; however, unlike pelletization, extrusion does not affect as much the compaction of the particles as they are suspended in a liquid. Besides, in some cases the flowability, plasticity, or ability of the paste to withstand deformation upon extrusion can be enhanced by adding plasticizers. These are typical organic compounds based on cellulose or polyalcohols which facilitate the formation of the overall network. Generally, they are removed from the final extrudate composition by calcination. For those outside of France, the hospitality industry, or both, the initials MOF may not ring a bell, but those three letters hold an incredible amount of significance. To be a “Meilleur Ouvrier de France” or "Best Craftsman of France" as you'll soon discover, is a very prestigious title indeed. Here's how it happens.

Y. Zhao, Z. Song, X. Li, Q. Sun, N. Cheng, S. Lawes and X. Sun, Metal organic frameworks for energy storage and conversion, Energy Storage Mater., 2016, 2, 35–62, DOI: 10.1016/j.ensm.2015.11.005.Two step, continuous flow spray-drying method, dense structures Garzon-Tovar et al. 138 also reported the spray-drying of a series of MOFs with high-nuclearity. To do so, they combined continuous flow and spray-drying methods ( Fig. 16b and c). As in the case of Mitsuka et al., 137 the former is beneficial to initiate the nucleation step, while the latter favors the crystal growth. Thus, the so-called spray-drying continuous flow-assisted synthesis was applied to produce spherical microbeads of UiO-66 and its derivatives. The process parameters entirely depend on the initial powder to be shaped. Mainly, the pressure applied on it should be carefully selected to avoid the complete destruction of the crystal structure (amorphization) and therefore loss of intrinsic properties. Additionally, the rate of pressure increase should be adequate for the same reason.