Following spinodal decomposition, which is also a phase separation method, Hara et al. 155 prepared UiO-66_NH 2-based monolithic materials with a trimodal pore structure. For that, all MOF precursors were dissolved into DMF along with poly(propylene glycol) (PPG) at 60 °C, and the clear solution was sealed in a hydrophobic glass tube kept at 80 °C. After 12 hours, hydrophilic UiO-66_NH 2 MOF mismatched growth occurred, as well as phase separation with the hydrophobic PPG. After washing with solvent, PPG was evacuated from the monolithic solid, leading to the formation of macropores whose diameter, between 0.9 and 1.8 μm, can be controlled by the amount of PPG. The XRD patterns displayed a few broad reflections, with 2 θ positions comparable to those of the simulated UiO-66. The structural properties of the MOF were proven by FT-IR spectroscopy, yielding a spectrum comparable to that of standard UiO-66_NH 2 powder. All samples presented specific surface areas between 712 and 749 m 2 g −1, further underlining the presence of a microporous network, while interparticular mesoporosity could also be deduced from N 2 sorption isotherms at higher relative pressure. Indeed, the TEM images showed particles with sizes below 50 nm. Uniaxial compression tests demonstrated that these monoliths presented a maximal compressive strength of 2.5 MPa. Interestingly, the authors showed that addition of acetic acid, a known modulator accelerating the crystallization, allowed obtaining larger mesopores. Alternatively, a post-shaping solvothermal treatment also allowed controlling the final size of the mesopores following the secondary growth of the MOF crystals. J. Alcañiz-Monge, G. Trautwein, M. Pérez-Cadenas and M. C. Román-Martínez, Effects of compression on the textural properties of porous solids, Microporous Mesoporous Mater., 2009, 126, 291–301, DOI: 10.1016/j.micromeso.2009.06.020.

The XRD patterns of the monoliths were found to be comparable to those of their powder analogues, suggesting that the crystal structure was retained upon shaping. The intensities however experienced a certain decrease, which was attributed to the presence of PVA. Further analyses revealed pronounced textural properties for Ni(bdc)(ted) 0.5 as given by N 2 physisorption. Its monolithic form exhibited a S BET of 1325 m 2 g −1, while its powder form presented a S BET of 1802 m 2 g −1. The difference was 27%, a value which agrees well with the initial MOF content in the paste (80 wt%). The corresponding values for ZIF-7 were 16 and 40 m 2 g −1, respectively, for its powder and printed forms. Its porosity is inaccessible to N 2 and the slightly higher available surface area was attributed to the silica binder in the printed composition. Interestingly, conventional compression tests revealed an excellent mechanical stability of up to 1.7 MPa for Ni(bdc)(ted) 0.5 due to the high content of binder (20 wt%), which provided considerably strong bonding of particles. At the same time, ZIF-7 monoliths withstood compression up to 0.8 MPa, showing that silica might be less appropriate than PVA for strongly bonding MOF particles. When probed for ethane/ethylene adsorption, Ni(bdc)(ted) 0.5 monoliths showed total uptakes of 4.1 and 2.9 mmol g −1, respectively. These values were found to be proportional to the MOF content. Notably, ZIF-7 monoliths showed total uptakes of 1.8 and 2.5 mmol g −1, respectively. Both isotherms exhibited an S-shape, revealing the pore-opening feature of this MOF upon increasing pressure. 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. 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. 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.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.” 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. 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). 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. 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.

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 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. The MOF title is really unique. It carries an important historical legacy and recognizes work approaching perfection. It is a true honor to receive recognition for one'speers and country. Today, I proudly represent and further with my best abilities the values of professional excellence, innovation and transmission.” explains Meilleur Ouvrier de France ChefChristian Segui What is the competition about? The extrudates were further applied for CO 2 and water-vapor adsorptions. The latter revealed identical isotherm shapes for both the powder and extrudates. This suggests that the intrinsic hydrophilicity/hydrophobicity balance of HKUST-1 was not altered upon shaping. Besides, CO 2 adsorption experiments at 25 °C revealed gravimetric uptakes of 218 and 129 mg g −1 for the MOF in powder and extruded forms, respectively. The decrease of CO 2 uptake demonstrated by the latter is in agreement with the loss in specific surface area upon extrusion. Liang et al. 149 studied the shaping of a Ti-based MIL-125 MOF with chitosan as a binding biopolymer into spherical beads. They first mixed chitosan and an FeCl 3 solution, followed by the addition of the MOF. Once well mixed, a 3% Na 5P 3O 10 solution was added dropwise to initiate the cross-linking step ( Fig. 17g). The thus-formed beads were recovered, washed and dried. The authors showed that such a formulation had no impact on the crystal structure nor the framework composition as confirmed by XRD, FTIR spectroscopy and XPS analyses. Therefore, the beads exhibited a consequent capacity for the removal of Pb( II) species, with only an ∼12% decrease in efficiency (from 100 to 88 mg g −1) after five consecutive cycles.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.

Ligand codes: BTC – benzene-1,3,5-tricarboxylic acid; BDC – benzene-1,4-dicarboxylic acid; BPTC – biphenyl-3,3′,5,5′-tetracarboxylic acid; BTB – 1,3,5-tris(4-carboxyphenyl)benzene; DHBDC – 2,5-dihydroxy-1,4-benzenedicarboxylic acid; FA – fumaric acid; MIM – 2-methyl imidazole; IP – isophthalate; BPY – 4,4′-bipyridine; NDC – naphthalenedicarboxylic acid; and L – 1 H-pyrazole-4-carboxylic acid. Spray-dryer codes: B-290 – B-290 Mini Spray Dryer (Büchi Labortechnik); SD-1000 – SD-1000 Spray Dryer (Tokyo Rikakikai); and AF-88 – AF-88 Laboratory Spray Dryer (AFIND Scientific Instrument Co. Ltd). “—” not specified.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. 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. Granulation is the last industrially-mature technology reviewed herein, and allows producing millimeter-sized grains. Two types of granulation techniques are typically discussed: wet granulation, when powders are aggregated in a high-shear rate mixer in the presence of a solvent; and dry granulation, when grains are obtained from a previously shaped object either mildly crushed and sieved, or spheronized. Due to higher stresses applied, the dry granulation implies more severe losses in the initial physicochemical properties of the MOFs, while the wet granulation has a less pronounced effect and therefore might be more adequate. Especially, replacing water with another solvent with a lower surface tension is highly beneficial. 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.