Fig. 6 Schematic representation of the extrusion process on a piston-type extruder (a) and on a single screw-type extruder (b).

R. Zacharia, D. Cossement, L. Lafi and R. Chahine, Volumetric hydrogen sorption capacity of monoliths prepared by mechanical densification of MOF-177, J. Mater. Chem., 2010, 20, 2145–2151, 10.1039/B922991D. C. Perego and P. Villa, Catalyst preparation methods, Catal. Today, 1997, 34, 281–305, DOI: 10.1016/S0920-5861(96)00055-7. 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. Z. R. Herm, R. Krishna and J. R. Long, CO 2/CH 4, CH 4/H 2 and CO 2/CH 4/H 2 separations at high pressures using Mg 2(dobdc), Microporous Mesoporous Mater., 2012, 151, 481–487, DOI: 10.1016/j.micromeso.2011.09.004.

The impact of compression on the textural and crystalline properties of MIL-53, as well as on its CO 2 sorption properties, was also studied by Ribeiro et al. 37 They compressed MIL-53 at 62 and 125 MPa with no binder added. The crystallinity was preserved even upon densification at 125 MPa as the XRD patterns were identical to their original powder counterpart. There is, however, a small shift of the reflections towards larger 2 θ values. The authors attributed this phenomenon to the structural deformations of the framework upon compression, in accordance with the results provided by Majchrzak-Kuceba and Sciubidlo. 36 In addition, it was shown that the textural properties were altered accordingly. Thus, MIL-53 lost 46 and 32% of the available surface as well as 36 and 24% of the pore volume, which can be partly attributed to the transition from a system of large pores to narrow pores, upon densification at 125 and 62 MPa, respectively. Interestingly, a broad distribution of macropores at around 230 nm was observed. Furthermore, the CO 2 adsorption capacity of MIL-53 decreased from 5.2 mol kg −1 to 3.7 and 4.0 mol kg −1 when compressed at 1.5, 62, and 125 MPa, respectively. The reduced gas uptake is thus consistent with the decrease in pore volume. Therefore, pelletization is considered as an appropriate shaping method for this MOF. ZIF-8 Ribeiro et al. 37 also extended their study to ZIF-8. As in the case of MIL-53, the ZIF-8 crystallinity was preserved even upon densification at 125 MPa as the XRD patterns matched with the original powder counterpart. In addition, it was shown that its textural properties were altered accordingly. Thus, ZIF-8 experienced only 7 and 12% loss in BET surface area as well as in pore volume when compressed at 62 and 125 MPa, respectively. Interestingly, it was demonstrated that densification led to the creation of macropores with diameters of about 300 nm and a distribution narrower than in the case of MIL-53. Furthermore, the CO 2 adsorption capacity decreased with the pore volume, from 9.0 mol kg −1 with the initial powder, to 8.7 (−3%) and 8.5 mol kg −1 (−6%) with pellets pressed at 62 and 125 MPa, respectively. The “Meilleur Ouvrier de France”competition was created in France in 1924 with the objective to revive the dwindling number of traditional craftsmen in France and recognize those who represent “high qualification in the exercise of a professional activity in the craft, commercial, service, industrial or agricultural.” Ligand codes: BTC – benzene-1,3,5-tricarboxylic acid; CA – citric acid; BDC – benzene-1,4-dicarboxylic acid; MIM – 2-methyl imidazole; TED – 1,4-biazabicyclo[2.2.2]octane; BiM – benzimidazole; PZDC – pyrazine-2,3-dicarboxylic acid; PYZ – pyrazine; and FA – fumaric acid. Binder/matrix codes: ABS – acrylonitrile-butadiene-styrene; PLA – polylactic acid; TPU – thermoplastic polyurethane; PVA – polyvinyl alcohol; HEC – 2-hydroxyethyl cellulose; SA – sodium alginate; TMPPTA – trimethylolpropane propoxylate triacrylate; PEA – 2-phenoxyethyl acrylate; PGD – polyethylene glycol diacrylate; PA12 – polyamide 12; and AAm – acrylamide + N, N′-methylenebisacrylamide (0.06 wt% acrylamide). Plasticizer codes: MC – methyl cellulose; HPC – hydroxypropylcellulose; DMSO – dimethyl sulfoxide; TOCNF – 2,2,6,6-tetramethylpiperidine-1-oxyl radical-mediated oxidized cellulose nanofibers; PVP – polyvinylpyrrolidone; and PVDF-HFP – poly(vinylidene fluoride- co-hexafluoropropylene). Photoinitiator codes: HMPP – 2-hydroxy-2-methylpropiophenone; PPO – phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; I-189 – Irgacure-819; I-184 – Irgacure-184; and I-2959 – Irgacure-2959. “—” not specified. Fig. 4 Typical wet granulation equipment: a high shear-rate mixer (Maschinenfabrik Gustav Eirich GmbH & Co KG), also referred to as a granulating pan (a) with an adjustable speed and direction of rotation; and a disc pelletizer (ERWEKA GmbH) also referred to as a rolling machine (b) with a controllable speed and inclination angle. Schematic representation of the wet granulation process: (c) mixing; (d) wetting and nucleation; (e) growth; and (f) spherization by attrition and breakage. 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.

F. Lorignon, A. Gossard and M. Carboni, Hierarchically porous monolithic MOFs: An ongoing challenge for industrial-scale effluent treatment, Chem. Eng. J., 2020, 393, 124765, DOI: 10.1016/j.cej.2020.124765. R. V. Jasra, B. Tyagi, Y. M. Badheka, V. N. Choudary and T. S. G. Bhat, Effect of Clay Binder on Sorption and Catalytic Properties of Zeolite Pellets, Ind. Eng. Chem. Res., 2003, 42, 3263–3272, DOI: 10.1021/ie010953l. S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant, A. G. Orpen and I. D. Williams, A Chemically Functionalizable Nanoporous Material [Cu 3(TMA) 2(H 2O) 3]n, Science, 1999, 283, 1148–1151, DOI: 10.1126/science.283.5405.1148. R. Bingre, B. Louis and P. Nguyen, An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations, Catalysts, 2018, 8, 163, DOI: 10.3390/catal8040163. Generally, extruders are divided into screw and piston types. The former allows continuous processing and might consist of one (single screw), two (twin screw) or multiple screws which operate in simultaneous and parallel rotations. On the other hand, piston extruders operate in batch mode; however, they enable the extrusion of pastes with high viscosity and compaction.

As in the case of extrusion, the paste formulation is a crucial step in 3D printing and should yield a final composition with appropriate rheological properties. Apart from the parent powder and a liquid, the paste is also composed of a binder and a plasticizer. The former provides adequate mechanical resistance to the final 3D objects, while the latter improves the flowability and plasticity of the paste to be printed. One of the major differences is the printing nozzle: while the die in extruders can reach sizes up to a few centimeters, in 3D printers the nozzle (or needle) is typically smaller than millimeters in diameter. Such a thin nozzle allows designing objects with complex geometries that would be challenging to obtain via a conventional method. 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. Bis ( (2-ethylhexyl)oxy)benzo[1,2-b 4,5-b’]dithiophene-2,6-diyl)bis (trimethylstannane) MOF Description 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.

A further study done by Boix et al. 143 in Maspoch's group led to the incorporation of inorganic nanoparticles into UiO-66 microbeads. The process followed the same sequence of steps, including the formation of primary nuclei in the flow reactor at 115 °C with a feed rate of 2.4 mL min −1, an inlet temperature of 180 °C, and a flow rate of 336 mL min −1. The thus-formed UiO-66 microbeads exhibited an average size of 1.5 ± 1.0 μm with a crystalline framework corresponding to the UiO-66. Additionally, the beads had a high surface area ( S BET = 945 m 2 g −1), which was slightly below than the one obtained by Garzon-Tovar et al. ( S BET = 1106 m 2 g −1) 138 following the same method. The difference might be attributed to the Zr-source used in each case: zirconium propoxide and zirconium tetrachloride, respectively. Interestingly, the UiO-66 itself was shown to be active towards the adsorption of toxic heavy metals such as Cr( VI) and As( V) with removal efficiencies of 99 and 45%, respectively. However, once functionalized with thiol (–SH) groups and doped with CeO 2 nanoparticles, it became active and efficient towards heavier metal species including Cd( II), Cu( II), Pb( II) and Hg( II) with removal efficiencies of 87, 99, 99 and 98%, respectively. Importantly, CeO 2-doped UiO-66-(SH) 2 microbeads retained their removal efficiency after 10 adsorption/desorption cycles in a continuous flow column, making them appropriate for further developments as water-purifying adsorbents. Peterson et al. 47 performed another study on HKUST-1 to examine the evolution of its physical and chemical properties. Thus, the authors applied pressures of 1000 psi (∼7 MPa) and 10 000 psi (∼69 MPa). While the crystal structure was globally preserved, compressed HKUST-1 exhibited broader reflections as well as high signal-to-noise ratios on the XRD patterns. This suggests partial framework damage. Consequently, there was a certain decrease in BET surface area, from 1698 m 2 g −1 for the powder to 892 m 2 g −1 for the pellets made at ∼69 MPa. These values are somewhat different from the ones reported by Kim et al., 48 who stated that above 10 MPa the HKUST-1 framework underwent structural degradation. At the same time, Dhainaut et al. 49 reported a low (15%) loss in BET surface area for HKUST-1, reaching 1091 m 2 g −1 upon densification at 121 MPa. Besides, they showed that addition of 2 wt% of a binder (graphite) slightly improved the mechanical stability of HKUST-1 pellets without significant loss of BET surface area. They explained this relatively small loss as due to the presence of the remaining solvent within the framework, acting as a scaffold during compression, as well as the slow compression speed applied to the powder bed. 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. A. Dhakshinamoorthy, Z. Li and H. Garcia, Catalysis and photocatalysis by metal organic frameworks, Chem. Soc. Rev., 2018, 47, 8134–8172, 10.1039/C8CS00256H.

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Fig. 1 Schematic representation of the pelletization process applied to polycrystalline MOF powder. S)-2-(2′-(bis (4-(trifluoromethyl)phenyl) phosphino)biphenyl-2-yl)-4-phenyl-4,5-dihydrooxazole MOF Description