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. 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.

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 Sébastien Royer obtained his PhD in Chemical Engineering from Laval University – QC – CA in 2004. Since 2015, he has been Full Professor at the University of Lille – FR. He leads the MATCAT research group from UCCS laboratory as well as the UPCAT technological platform devoted to the study of catalyst scale-up (up to 10 kg) and shaping. S. Royer has done research in the fields of catalytic materials engineering, with interest in control of porosity (mesoporous, macroporous, and hierarchical porosity), dispersion and stability of metallic elements, long term stability and regeneration procedures, characteristics of shaped catalysts. The MOF competition and its preparation are definitely in my top lifetime memories. The hours of preparation, the stress of the competition, the recognition for all the work and commitment, have alla All has changed me forever. I have pushed myself beyond what I imagined possible and it certainly contributed in making me a better professional.” continues Meilleur Ouvrier de France Chef Thomas Marie The culinary connectionFig. 9 Schematic representation of the 3D printing process via the Direct Ink Writing (DIW) method. Among other studies on ZIF-8 densification, there is a study by Bazer-Bachi et al. 39 (who also densified SIM-1). The authors applied a wide range of pressures and showed that the crystallinity of ZIF-8 was preserved upon compression up to ∼230 MPa. At the same time, the loss in BET surface area was about 11%, with the ZIF-8 pellet reaching 1278 m 2 g −1, while the pristine ZIF-8 powder exhibited 1433 m 2 g −1. Noteworthily, these results are in good agreement with the ones reported by Ribeiro et al. 37 and Chapman et al. 38 Upon compression, SIM-1 demonstrated a similar trend with a 28% drop in surface area (516 vs. 370 m 2 g −1) at a decent pressure of ∼400 MPa while preserving its framework topology according to its XRD pattern. 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. 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 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.

Tian et al. 160 showed the possibility to form ZIF-8 monoliths without using binders nor high pressures. For this, they immersed a newly-formed ZIF-8 powder into an ethanolic solution containing dissolved precursors (Zn-nitrate and methylimidazole), and the solid product was recovered via centrifugation. The authors outlined the importance of drying the solid at room temperature so that it retained its monolithic shape. Besides, when extra amounts of precursors were added, mechanically stable monoliths were formed due to the extension of polymerization reactions. The mechanical resistance was assessed by measuring the elastic modulus (7 GPa) and hardness (0.6 GPa) by nanoindentation. The thus-formed monoliths retained the original crystal structure of ZIF-8 as well as high specific surface area, up to 1395 m 2 g −1. 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. Avci-Camur et al. 141 continued exploiting the spray-drying technique for the synthesis of MOFs, targeting the UiO-66 family and more specifically UiO-66-NH 2 by the combined continuous-flow spray-drying method under aqueous conditions. For this purpose, the authors used water-soluble ZrOCl 2·8H 2O and 2-aminoterephthalic acid as the metal-precursor and the ligand, respectively. In this work specific stress was given to the use of a modulator, the acetic acid. Generally, the application of monotopic acids such as hydrochloric, formic and acetic acids facilitates the formation/crystallization of the UiO-family of MOFs. 142 Accordingly, it was shown that an increase in the acid concentration caused significant changes in textural properties. Thus, the UiO-66-NH 2 prepared with 14% acetic acid in the feed solution yielded microbeads with a S BET of 840 m 2 g −1 when spray-dried at T coil = 90 °C, T in = 150 °C, flow rate = 336 mL min −1 and feed rate = 2.4 mL min −1. However, at elevated (56%) concentrations of the acid, the S BET significantly increased up to 1036 m 2 g −1 under the same operating conditions. It should be noted that a further increase (70%) in the acid content led to a partial loss in crystallinity viewed as a decrease in reflection intensities in the XRD pattern as well as a loss in S BET down to 655 m 2 g −1. This suggests a competition between the modulator and the ligand for coordination with the metal clusters and therefore subsequent structural collapse upon exceeding occupation of the clusters by the modulator. The optimal acid concentration was found to be 30%. At this value, the spray-dried UiO-66-NH 2 yielded microbeads with a size distribution of 4–10 μm ( Fig. 16e) and exhibiting the UiO-66 structure according to XRD results. Besides, the S BET value, 1261 m 2 g −1, lies in the range of non-functionalized UiO-66 made via the solvothermal route with DMF, and is much higher than that of the spray-dried UiO-66-NH 2 prepared by Garzon-Tovar et al. ( S BET = 752 m 2 g −1). 138 Finally, the same protocol was applied to the Zr-fumarate MOF. The corresponding information is given in Table 14. The craftsmanship exhibition has been held every three to four years and showcases different professions including florists, carpenters, butchers, jewelry makers, and of course pastry chefs, to name just a few. Along with the title, winners receive a medal and state diploma. 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.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. Moreira et al. 52 demonstrated the reverse selectivity of UiO-66 towards liquid-phase separation of xylene isomers. Indeed, the obtained results suggested o-xylene selectivities of 1.8 and 2.4 with respect to m- and p-xylene, at 40 °C with n-heptane as the eluent. Besides, the authors showed that the selectivities were retained upon compression, meaning that no major modification of the pore network took place upon compression. Interestingly, the authors stated that at low concentrations the selectivity values of UiO-66 were comparable to the ones previously reported for MIL-53. However, the latter failed to separate m- and p-isomers unlike UiO-66.

O. M. Yaghi and H. Li, Hydrothermal Synthesis of a Metal–Organic Framework Containing Large Rectangular Channels, J. Am. Chem. Soc., 1995, 117, 10401–10402, DOI: 10.1021/ja00146a033. Mater. Adv., 2021, 2, 7139-7186 From metal–organic framework powders to shaped solids: recent developments and challenges Finally, Lawson et al. 111 studied the post-printing crystallization of HKUST-1 starting from a gel containing all precursors. In this case, a mixture of bentonite (21 wt%), methylcellulose (2 wt%) and PVA (6 wt%) was used to obtain satisfactory rheological properties. The as-printed grids presented a fair replication of the initial model, and they were further placed in a convection oven at 120 °C for 20 hours to induce crystallization of the MOF. The resulting material presented a S BET of 500 m 2 g −1, slightly higher than that of a comparative solid directly 3D-printed starting from the HKUST-1 powder (470 m 2 g −1). While the solids were extensively washed with acetone, residual DMF was observed by FTIR spectroscopy as characterized by a band at 2100 cm −1. Finally, the CO 2 capacities of both solids at 25 °C were compared. While the solid prepared from the HKUST-1 powder presented a CO 2 capacity 50% higher (2.1 mmol g −1 against 1.4 mmol g −1), which is not in line with their respective S BET, the solid obtained by growing HKUST-1 crystals on the as-printed solid displayed enhanced mass transfer kinetics (diffusivity × 10 8 (cm 2 s −1): 8.75 against 5.25). This was attributed to the presence of a larger extent of mesopores ( V meso (cm 3 g −1 STP) = 0.16 against 0.09).J. J. Purewal, D. Liu, J. Yang, A. Sudik, D. J. Siegel, S. Maurer and U. Mu, Increased volumetric hydrogen uptake of MOF-5 by powder densification, Int. J. Hydrogen Energy, 2012, 37, 2723–2727, DOI: 10.1016/j.ijhydene.2011.03.002. Moreover, spray-drying allows the direct synthesis of various materials. 128 In 2002, du Fresne von Hohenesche et al. 129 successfully prepared MCM-41 spherical microbeads with a defined arrangement of macro- and mesopores with the help of a spray-dryer. Since then, the same approach has been used for preparation of other types of porous materials, 130 allowing spray-drying to be considered as a tool for simultaneous synthesis and shaping. 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. 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.

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.A. Dailly and E. Poirier, Environmental Science Evaluation of an industrial pilot scale densified MOF-177 adsorbent as an on-board hydrogen storage medium, Energy Environ. Sci., 2011, 4, 3527–3534, 10.1039/C1EE01426A. 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 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. Y. H. Hu and L. Zhang, Amorphization of metal–organic framework MOF-5 at unusually low applied pressure, Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 81, 174103, DOI: 10.1103/PhysRevB.81.174103. L. Wang, M. Zheng and Z. Xie, Nanoscale metal–organic frameworks for drug delivery: a conventional platform with new promise, J. Mater. Chem. B, 2018, 6, 707–717, 10.1039/C7TB02970E.