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Bis ( (2-ethylhexyl)oxy)benzo[1,2-b 4,5-b’]dithiophene-2,6-diyl)bis (trimethylstannane) MOF Product 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). Q. Wang and D. Astruc, State of the Art and Prospects in Metal−Organic Framework (MOF) – Based and MOF-Derived Nanocatalysis, Chem. Rev., 2020, 120, 1438–1511, DOI: 10.1021/acs.chemrev.9b00223. In 2015, Crawford et al. 92 described the mechanochemical synthesis of MOFs using a twin screw extruder (TSE) ( Fig. 7g), thus combining synthesis and shaping in one step. Indeed, the rotating screws composed of different zones (conveying, shearing, kneading) displace the starting solid MOF precursors along the heated barrel with good control over the residence time, and the mixing duration and intensity. Hence, through the combination of shearing and compression forces, solid-state reactions between the precursors can be obtained. Ideally, upon reaching the exit port, the product is formed and it is further drawn through a die into extrudates. Of note, the controllable heating of the barrel allows better control over the reaction conditions as compared to conventional milling approaches.

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. 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.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. C. Perego and P. Villa, Catalyst preparation methods, Catal. Today, 1997, 34, 281–305, DOI: 10.1016/S0920-5861(96)00055-7.

Bis ( (2-ethylhexyl)oxy)benzo[1,2-b 4,5-b’]dithiophene-2,6-diyl)bis (trimethylstannane) MOF Description formulation of powders into mechanically stable objects to withstand a variety of process conditions (elevated pressure, gas/liquid flow, mixing); 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. 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. 99Some 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. C. Wang, Y. V. Kaneti, Y. Bando, J. Lin, C. Liu, J. Li and Y. Yamauchi, Metal–organic framework-derived one-dimensional porous or hollow carbon-based nanofibers for energy storage and conversion, Mater. Horiz., 2018, 5, 394–407, 10.1039/C8MH00133B.

A. Dhakshinamoorthy, Z. Li and H. Garcia, Catalysis and photocatalysis by metal organic frameworks, Chem. Soc. Rev., 2018, 47, 8134–8172, 10.1039/C8CS00256H. 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. 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. 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.

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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).

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. 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 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. 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. 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. 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.