Advancing Membrane Technology: Ordered Macroporous ZIF-67 as a Filler in Mixed Matrix Membranes for Enhanced Propylene/Propane Separation.

Conventional separation technologies for valuable commodities require substantial energy, accounting for 10%-15% of global consumption. Mixed-matrix membranes (MMMs) offer a promising solution by combining processable polymers with selective inorganic fillers. Here, the potential of using ordered microporous structured materials is demonstrated as MMM fillers. The use of ordered macroporous ZIF-67 in combination with the well-known 6FDA-DAM polymer leads to superior performance in the important separation of propylene from propane. The enhanced performance can be rationalized with the help of advanced microscopy, which demonstrates that the polymer is able to penetrate the macroporous network around which the MOF (Metal-Organic Framework) is synthesized, resulting in a much better interphase between the two components and the homogeneous distribution of the filler, even at high loadings.

Solution processable metal-organic frameworks for mixed matrix membranes using porous liquids.

The combination of well-defined molecular cavities and chemical functionality makes crystalline porous solids attractive for a great number of technological applications, from catalysis to gas separation. However, in contrast to other widely applied synthetic solids such as polymers, the lack of processability of crystalline extended solids hampers their application. In this work, we demonstrate that metal-organic frameworks, a type of highly crystalline porous solid, can be made solution processable via outer surface functionalization using N-heterocyclic carbene ligands. Selective outer surface functionalization of relatively large nanoparticles (250 nm) of the well-known zeolitic imidazolate framework ZIF-67 allows for the stabilization of processable dispersions exhibiting permanent porosity. The resulting type III porous liquids can either be directly deployed as liquid adsorbents or be co-processed with state-of-the-art polymers to yield highly loaded mixed matrix membranes with excellent mechanical properties and an outstanding performance in the challenging separation of propylene from propane. We anticipate that this approach can be extended to other metal-organic frameworks and other applications.

Spray-Drying Synthesis of MOFs, COFs, and Related Composites.

ConspectusMetal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are among the most attractive porous materials today. They exhibit outstanding porosity for countless applications such as gas storage, CO2 capture, gas separation, sensing, drug delivery, and catalysis. Moreover, researchers have recently begun to combine MOFs or COFs with other functional materials to obtain composites that boast the respective strengths, and mitigate the respective weaknesses, of each component, enabling enhanced performance in many of the aforementioned applications. Accordingly, development of methods for fabrication of MOFs, COFs, and related composites is important for facilitating adoption of these materials in industry. One promising synthetic technique is spray-drying, which is already well-integrated in manufacturing processes for diverse sectors. It enables rapid, continuous and scalable production of dry microspherical powders in a single step, leading to lower fabrication costs and shorter production times compared to traditional methods.In this Account, we outline our ongoing work on spray-drying synthesis of crystalline porous MOFs, COFs, and related composites. Versatile and tunable, spray-drying can be adapted to perform reactions involving coordination and covalent chemistry for the synthesis of micrometer spherical beads/superstructures of MOFs and COFs. Likewise, MOF- and COF-based composites can be synthesized using similar conditions as those for pure MOFs or COFs, through the simple introduction of additional functional materials into the feed precursor solution or colloid. Interestingly, spray-drying can also be done in water, thus providing the basis for its use as a scalable green method for industrial fabrication of these materials. To date, spray-drying has already been scaled up for pilot production (kilogram scale) of MOFs.

An Efficient Metal-Organic Framework-Derived Nickel Catalyst for the Light Driven Methanation of CO2.

We report the synthesis of a highly active and stable metal-organic framework derived Ni-based catalyst for the photothermal reduction of CO2 to CH4 . Through the controlled pyrolysis of MOF-74 (Ni), the nature of the carbonaceous species and therefore photothermal performance can be tuned. CH4 production rates of 488 mmol g-1 h-1 under UV-visible-IR irradiation are achieved when the catalyst is prepared under optimized conditions. No particle aggregation or significant loss of activity were observed after ten consecutive reaction cycles or more than 12 hours under continuous flow configuration. Finally, as a proof-of-concept, we performed an outdoor experiment under ambient solar irradiation, demonstrating the potential of our catalyst to reduce CO2 to CH4 using only solar energy.

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation.

Herein, we describe a new class of porous composites comprising metal-organic framework (MOF) crystals confined in single spherical matrices made of packed covalent-organic framework (COF) nanocrystals. These MOF@COF composites are synthesized through a two-step method of spray-drying and subsequent amorphous (imine-based polymer)-to-crystalline (imine-based COF) transformation. This transformation around the MOF crystals generates micro- and mesopores at the MOF/COF interface that provide far superior porosity compared to that of the constituent MOF and COF components added together. We report that water sorption in these new pores occurs within the same pressure window as in the COF pores. Our new MOF@COF composites, with their additional pores at the MOF/COF interface, should have implications for the development of new composites.

Spray Drying for Making Covalent Chemistry: Postsynthetic Modification of Metal-Organic Frameworks.

Covalent postsynthetic modification (PSM) of metal-organic frameworks (MOFs) has attracted much attention due to the possibility of tailoring the properties of these porous materials. Schiff-base condensation between an amine and an aldehyde is one of the most common reactions in the PSM of MOFs. Here, we report the use of the spray drying technique to perform this class of organic reactions, either between discrete organic molecules or on the pore surfaces of MOFs, in a very fast (1-2 s) and continuous way. Using spray drying, we show the PSM of two MOFs, the amine-terminated UiO-66-NH2 and the aldehyde-terminated ZIF-90, achieving conversion efficiencies up to 20 and 42%, respectively. Moreover, we demonstrate that it can also be used to postsynthetically cross-link the aldehyde groups of ZIF-90 using a diamine molecule with a conversion efficiency of 70%.

Continuous One-Step Synthesis of Porous M-XF6 -Based Metal-Organic and Hydrogen-Bonded Frameworks.

Metal-organic frameworks (MOFs) built up from connecting M-XF6 pillars through N-donor ligands are among the most attractive adsorbents and separating agents for CO2 and hydrocarbons today. The continuous, one-step spray-drying synthesis of several members of this isoreticular MOF family varying the anionic pillar (XF6 =[SiF6 ]2- and [TiF6 ]2- ), the N-donor organic ligand (pyrazine and 4,4'-bipyridine) and the metal ion (M=Co, Cu and Zn) is demonstrated here. This synthetic method allows them to be obtained in the form of spherical superstructures assembled from nanosized crystals. As confirmed by CO2 and N2 sorption studies, most of the M-XF6 -based MOFs synthesised through spray-drying can be considered "ready-to-use" sorbents as they do not need additional purification and time consuming solvent exchange steps to show comparable porosity and sorption properties with the bulk/single-crystal analogues. Stability tests of nanosized M-SiF6 -based MOFs confirm their low stability in most solvents, including water and DMF, highlighting the importance of protecting them once synthesised. Finally, for the first time it was shown that the spray-drying method can also be used to assemble hydrogen-bonded open networks, as evidenced by the synthesis of MPM-1-TIFSIX.

Hexa-kis-(dimethyl sulfoxide-κO)zinc(II) poly-iodide.

The title compound, [Zn{(CH3)2SO}6]I4, is a one-dimensional supra-molecular polymer along a threefold rotation axis of the space group. It is built up from discrete [Zn{(CH3)2SO}6](2+) units connected through non-classical hydrogen bonds to linear I4 (2-) polyiodide anions (C-H⋯I = 3.168 Å). The Zn(II) ion in the cation has an octa-hedral coordination geometry, with all six Zn-O bond lengths being equivalent, at 2.111 (4) Å. The linear polyiodide anion contains a neutral I2 mol-ecule weakly coordinated to two iodide ions.

Ruthenium-Picolylamine-Incorporated Mixed-Linker MOFs: Highly Active Heterogeneous Catalysts for Olefin and Aldehyde Hydrogenation.

The selective hydrogenation of aldehydes and olefins plays a crucial role in the synthesis of various industrial products. Immobilizing noble metal catalysts on solid supports has been pursued to overcome the challenges associated with catalyst separation and recovery. In this study, we explore the use of metal-organic frameworks (MOFs) as supports for the immobilization of molecular ruthenium catalysts in the hydrogenation of olefins and aldehydes. We designed a mixed-linker MOF by incorporating the picolylamine moiety, which is a ligand known for its excellent catalytic activity. The ruthenium catalysts were prepared via a simple metal-ligand coordination process without the need for additional treatments. The resulting catalysts exhibit high catalytic activity and a uniform distribution of ruthenium sites on the MOF crystals. The choice of ruthenium precursor has a significant influence on the catalytic performance, with even lower metal content resulting in higher activity. The catalysts achieve high conversion rates and selectivities in the hydrogenation of various olefins. However, in the hydrogenation of aldehydes, due to the harsher conditions required, the formation of small nanoparticles is observed after the reaction. Overall, our findings highlight the potential of picolylamine-modified MOFs as effective supports for the development of highly active heterogeneous catalysts for selective hydrogenation reactions.

MOF-Beads Containing Inorganic Nanoparticles for the Simultaneous Removal of Multiple Heavy Metals from Water.

Pollution of water with heavy metals is a global environmental problem whose impact is especially severe in developing countries. Among water-purification methods, adsorption of heavy metals has proven to be simple, versatile, and cost-effective. However, there is still a need to develop adsorbents with a capacity to remove multiple metal pollutants from the same water sample. Herein, we report the complementary adsorption capacities of metal-organic frameworks (here, UiO-66 and UiO-66-(SH)2) and inorganic nanoparticles (iNPs; here, cerium-oxide NPs) into composite materials. These adsorbents, which are spherical microbeads generated in one step by continuous-flow spray-drying, efficiently and simultaneously remove multiple heavy metals from water, including As(III and V), Cd(II), Cr(III and VI), Cu(II), Pb(II), and Hg(II). We further show that these microbeads can be used as a packing material in a prototype of a continuous-flow water treatment system, in which they retain their metal-removal capacities upon regeneration with a gentle acidic treatment. As proof-of-concept, we evaluated these adsorbents for purification of laboratory water samples prepared to independently recapitulate each of two strongly polluted rivers: the Bone (Indonesia) and Buringanga (Bangladesh) rivers. In both cases, our microbeads reduced the levels of all the metal contaminants to below the corresponding permissible limits established by the World Health Organization (WHO). Moreover, we demonstrated the capacity of these microbeads to lower levels of Cr(VI) in a water sample collected from the Sarno River (Italy). Finally, to create adsorbents that could be magnetically recovered following their use in water purification, we extended our spray-drying technique to simultaneously incorporate two types of iNPs (CeO2 and Fe3O4) into UiO-66-(SH)2, obtaining CeO2/Fe3O4@UiO-66-(SH)2 microbeads that adsorb heavy metals and are magnetically responsive.

Photothermal Activation of Metal-Organic Frameworks Using a UV-Vis Light Source.

Metal-organic frameworks (MOFs) usually require meticulous removal of the solvent molecules to unlock their potential porosity. Herein, we report a novel one-step method for activating MOFs based on the photothermal effect induced by directly irradiating them with a UV-vis lamp. The localized light-to-heat conversion produced in the MOF crystals upon irradiation enables a very fast solvent removal, thereby significantly reducing the activation time to as low as 30 min and suppressing the need for time-consuming solvent-exchange procedures and vacuum conditions. This approach is successful for a broad range of MOFs, including HKUST-1, UiO-66-NH2, ZIF-67, CPO-27-M (M = Zn, Ni, and Mg), Fe-MIL-101-NH2, and IRMOF-3, all of which exhibit absorption bands in the light emission range. In addition, we anticipate that this photothermal activation can also be used to activate covalent organic frameworks (COFs).

The photothermal effect in MOFs: covalent post-synthetic modification of MOFs mediated by UV-Vis light under solvent-free conditions.

Here, we report the covalent post-synthetic modification (CPSM) of MOFs using the photothermal effect. Specifically, we subjected mixtures of a photothermally active MOF and another reagent to irradiation with a UV-Vis lamp. This caused the MOF to heat up, which in turn caused the other reagent to melt and subsequently react with the functional groups on the walls of the MOF pores. We have exploited this dual function of MOFs as both heater and host for CPSMs to achieve rapid formation of amides from the reaction of representative MOFs (UiO-66-NH2 or MIL-101-NH2-(Al)) with anhydrides under solvent-free conditions. In addition, this approach enables more complex CPSMs in MOFs such as the formation of amides in UiO-66-NH2 by using an aldehyde through a cascade reaction.

Spray drying for making covalent chemistry II: synthesis of covalent-organic framework superstructures and related composites.

Here we report a method that combines the spray-drying technique with a dynamic covalent chemistry process to synthesize zero-dimensional, spherical and microscale superstructures made from the assembly of imine-based COF nanocrystals. This methodology also enables the integration of other functional materials into these superstructures forming COF-based composites.

Synthesis and structure of [Na4(DMSO)15][(I3)3(I)]. Self-assembly of hexacoordinated sodium.

A new complex with the molecular formula [Na(4)(DMSO)(15)][(I(3))(3)(I)] represents the first example of Na(+) coordinated solely by DMSO. The triiodide (I(3)(-)) and iodide (I(-)) anions form an infinite linear chain running throughout the crystal.