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. S)-2-(2′-(bis (4-(trifluoromethyl)phenyl) phosphino)biphenyl-2-yl)-4-phenyl-4,5-dihydrooxazole MOF Description M. Mon, R. Bruno, J. Ferrando-Soria, D. Armentano and E. Pardo, Metal–organic framework technologies for water remediation: towards a sustainable ecosystem, J. Mater. Chem. A, 2018, 6, 4912–4947, 10.1039/C8TA00264A. Ligand codes: 1,3,5-BTC – benzene-1,3,5-tricarboxylic acid; 1,2,4-BTC – benzene-1,2,4-tricarboxylic acid; BDC – benzene-1,4-dicarboxylic acid; CA – citric acid; and MIM – 2-methyl imidazole. Binder codes: MSE – methoxy-siloxane ether; PVA – polyvinyl alcohol; PVC – polyvinyl chloride; KH570 – 3(trimethoxysilyl)propyl methacrylate; and MC – methyl cellulose. Plasticizer codes: MHPC – methyl hydroxyl propyl cellulose and DMF – N, N-dimethylformamide. “—” not specified. a Measured by Hg intrusion.

The MOF competition is a fierce one, requiring many months, sometimes years, of intense preparation. It aims to evaluate the dexterity, knowledge of modern and traditional techniques, know-how and creativity of candidates representing over 200 different professions, with artisans representing 16 industries as far-flung and diverse as hospitality, textiles, floral design, leatherworking, and ceramics. Within each category there are several smaller groups representing different specialties. Compaction itself serves as a source of reinforcement; however, sometimes the use of binders to enhance the mechanical stability of pellets is of particular interest. Binders are usually classified into organic binders such as starch, cellulose and polyvinyl alcohol (PVA) and inorganic binders such as clays, silica and graphite. 20 They facilitate bonding of individual particles by generating a link between them. As an example, it was shown that zeolites X and Y could be pelletized using bentonite as the binder, 21 and kaolinite could be employed to bind ZSM-5 zeolite crystals together. 22 In both cases there is an alteration of both the physical and chemical properties of the final materials compared to the pristine zeolites.An aqueous spray-drying synthesis of the Zn-imidazole ZIF-8 was done by Tanaka et al. 134 In a typical synthesis, an aqueous suspension containing Zn-acetate and 2-methylimidazole was spray-dried at T in = 150 °C and a feed rate of 5 mL min −1. These conditions yielded dense spherical particles with an average size of 3.9 μm as confirmed by SEM and TEM. However, the XRD results suggested the formation of an unknown phase different from that of the original ZIF-8. Moreover, the product poorly adsorbed nitrogen as revealed by N 2 sorption measurements. Notably, the authors observed the coordination of dissolved species and therefore the solution turning into a suspension right before spraying. The authors explained this phenomenon as due to the hindrance of crystallization created by acetic acid, a by-product originating from the Zn-precursor. The presence of the acid in the as-synthesized product was demonstrated by means of FTIR spectroscopy and TGA. Accordingly, during the spray-drying process, the as-released acetic acid caused a rearrangement of Zn-(2-methylimidazole) bonds, leading to the amorphization of the final product due to the incomplete coordination of the ligands around the metal. Interestingly, the presence of non-coordinated ligands was similarly evidenced by TGA. However, redispersing the spray-dried particles in an alcohol enabled the recrystallization and thus the formation of the targeted ZIF-8 framework. Interestingly, the size of the alcohol molecule influenced the size of the nanocrystals: specifically, the longer the carbon chain the larger the nanocrystals. However, the microbead size remained in the same range. Upon recrystallization, the product yielded an XRD pattern characteristic of ZIF-8 with a S BET of 1440 m 2 g −1, which is consistent with the results published elsewhere. 135 Surprisingly, once these ZIF-8 microbeads were redispersed in an alcoholic solution, they undergo a transition from dense to hollow superstructures. Hence, the recrystallization process is fed by gradually dissolving the amorphous by-product from the surface to the core of the microbeads. Linker codes: BDC – benzene-1,4-dicarboxylic acid; BTB – 1,3,5-benzenetribenzoate; MIM – 2-methyl imidazole; MIC – 4-methyl-5-imidazolecarboxaldehyde; BTC – benzene-1,3,5-tricarboxylic acid; DHBDC – 2,5-dihydroxy-1,4-benzenedicarboxylic acid; BPDC – biphenyl-4,4′-dicarboxylic acid; and FA – formic acid. Binder codes: PVA – polyvinyl alcohol; SB – pseudoboehmite; and PVB – polyvinyl butyral. “—” not specified. a Used as an additive to improve thermal conductivity. A mixture of PVA and PVB was used as a binder in the study by Chanut et al. 71 The authors first mixed 5 g of MOF powder with a 3 wt% polymer blend, followed by periodical spraying of ethanol for a total of 50 mL to cause primary particle agglomeration. Upon sieving, a fraction with sizes between 1.3 and 1.7 mm ( Fig. 5h) was rounded using a rolling device to achieve the final shape. Eventually, the spheres were dried at 110 °C for 12 h to remove the residual ethanol. 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. 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.

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.S)-2-(2′-(bis (4-(trifluoromethyl)phenyl) phosphino)biphenyl-2-yl)-4-phenyl-4,5-dihydrooxazole MOF Product Less than 10,000 people have ever won the right to call themselves one of the Best Craftsmen in France. MOF winners retain their title for life. Many choose to join the National Society of Meilleur Ouvrier de France, a sort of alumni society for winners. The title is taken so seriously that sporting such a collar fraudulently is a crime punishable by prison-time. Bakytzhan Yeskendir received his MSc in Chemistry and Spectroscopy in 2018 within the framework of the Advanced Spectroscopy in Chemistry Master Program funded by Erasmus Mundus. He is now pursuing his PhD in materials science in the fields of synthesis, characterization, upscaling and shaping of materials for application in catalysis and gas adsorption, with special interest in the design of catalysts and adsorbents based on Metal–Organic Frameworks and zeolites, as collaborating work between the MATCAT group led by Pr. Sébastien Royer at the Université de Lille and the LMCPA led by Pr. Christian Courtois at UPHF. Y. Ming, J. Purewal, J. Yang, C. Xu, R. Soltis, J. Warner, M. Veenstra, M. Gaab, U. Mu and D. J. Siegel, Kinetic Stability of MOF-5 in Humid Environments: Impact of Powder Densification, Humidity Level, and Exposure Time, Langmuir, 2015, 31, 4988–4995, DOI: 10.1021/acs.langmuir.5b00833.

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 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. Fig. 3 BET SSA as a function of applied pressure during pelletization (left): ( ) – ZIF-8 by Ribeiro et al., 37 ( ) – ZIF-8 by Bazer-Buchi et al., 39 ( ) – UiO-66-NH 2 by Peterson et al., 51 ( ) – UiO-66-NH 2 by Dhainaut et al., 49 ( ) – HKUST-1 by Bazer-Buchi et al., 39 ( ) – HKUST-1 by Dhainaut et al., 49 and ( ) – HKUST-1 by Alcañiz-Monge et al. 25 BET surface area as a function of bulk density (right): ( ) – MOF-177 by Zacharia et al., 32 ( ) – MIL-101 by Ardelean et al., 41 and ( ) – MOF-5 by Purewall et al. 28 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. a Attrition tests were performed by rotating a cylinder containing a baffle and the shaped UiO-66-COOH at 60 rpm for 30 min. The percentage corresponds to the total mass of the fine particles – less than 425 μm – after sieving.

R. R. Salunkhe, Y. V. Kaneti and Y. Yamauchi, Metal−Organic Framework-Derived Nanoporous Metal Oxides toward Supercapacitor Applications: Progress and Prospects, ACS Nano, 2017, 11, 5293–5308, DOI: 10.1021/acsnano.7b02796. On the other hand, the CPO-27 and MIL-100 frameworks proved to be more stable under the applied conditions, as the granules’ diffractograms yielded matching patterns with their powder counterparts. The MIL-100 granules presented only a slight decrease in SSA ( S BET = 1172 m 2 g −1), which is in the range of 2% loss as compared to the parent powder ( S BET = 1212 m 2 g −1), consistent with the initial amount of the binder. Surprisingly, the CPO-27 granules exhibited a considerable increase in specific surface area ( S BET = 1319 m 2 g −1) as compared to S BET = 937 m 2 g −1 of the as-synthesized CPO-27. This phenomenon was stated to be unclear by the authors. 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. G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S. Surblé and I. Margiolaki, A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area, Science, 2005, 309, 2040–2042, DOI: 10.1126/science.1116275. According to XRD results, the printed objects retained the original crystal structure of HKUST-1 upon formulation. A certain peak broadening was observed for all materials, suggesting small MOF crystals. Indeed, as confirmed by SEM, the shaped objects were composed of HKUST-1 crystals with sizes in the 20–50 nm range. However, a significant decrease of the S BET was measured, from 1850 m 2 g −1 for the parent powder to 1134 m 2 g −1 for the 3D-printed solids. As no binder was present, this decrease might be ascribed to the partial collapse of the HKUST-1 framework.