Functionalized NU-1000 with an Iridium Organometallic Fragment: SO2 Capture Enhancement

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Modulator-Dependent Dynamics Synergistically Enabled Record SO2 Uptake in Zr(IV) Metal-Organic Frameworks Based on Pyrene-Cored Molecular Quadripod Ligand

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal-organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g-1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in isostructural Zr-TPA variants synthesized with different capping modulators (formate, acetate, benzoate, and trifluoroacetate, abbreviated as FA, HAc, BA, and TFA, respectively) through computational analyses. These analyses revealed unexpected SO2-induced modulator-node dynamics, resulting in transient chemisorption that enhanced synergistic SO2 sorption. Additionally, we conducted a proof-of-concept experiment demonstrating that the captured SO2 in Zr-TPA-FA can be converted in situ into a valuable pharmaceutical intermediate known as aryl N-aminosulfonamide, with a high yield and excellent recyclability. This highlights the potential of robust Zr-MOFs for storing SO2 in catalytic applications. In summary, this work contributes significantly to the development of efficient SO2 solid sorbents and advances our understanding of the molecular mechanisms underlying SO2 sorption in Zr-MOF materials.

Unexpected alkyl isomerization at the silicon ligand of an unsaturated Rh complex: combined experiment and theory

The formation of dimer [(μ-Cl)Rh-(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)(o-C6H4CH2SiiPrnPr))]2 (Rh-3) with an n-propyl group on one of the silicon atoms as a minor product was affected by the reaction of [RhCl(COD)]2 with proligand PhP(o-C6H4CH2SiHiPr2)2, L1. The major product of the reaction was monomeric 14-electron Rh(III) complex [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2)] (Rh-1). Computations revealed that the monomer-dimer equilibrium is shifted toward the monomer with four isopropyl substituents on the two Si atoms of the ligand as in Rh-1; conversely, the dimer is favored with only one n-propyl as in Rh-3, and with less bulky alkyl substituents such as in [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiMe2)2]2 (Rh-2). Computations on the mechanism of formation of Rh-3 directly from [RhCl(COD)]2 are in agreement with the experimental findings and it is found to be less energetic than if stemming from Rh-1. Additionally, a Si-O-Si complex, [μ-Cl-Rh{κ3(P,Si,C)PPh(o-C6H4CH2SiiPrO SiiPr2CH-o-C6H4)}]2, Rh-4, is generated from the reaction of Rh-1 with adventitious water as a result of intramolecular C-H activation.

Structural and Dynamic Analysis of Sulphur Dioxide Adsorption in a Series of Zirconium‐Based Metal–Organic Frameworks

We report reversible high capacity adsorption of SO₂ in robust Zr‐based metal–organic framework (MOF) materials. Zr‐bptc (H₄bptc=biphenyl‐3,3′,5,5′‐tetracarboxylic acid) shows a high SO₂ uptake of 6.2 mmol g⁻¹ at 0.1 bar and 298 K, reflecting excellent capture capability and removal of SO₂ at low concentration (2500 ppm). Dynamic breakthrough experiments confirm that the introduction of amine, atomically‐dispersed Cu^II or heteroatomic sulphur sites into the pores enhance the capture of SO₂ at low concentrations. The captured SO₂ can be converted quantitatively to a pharmaceutical intermediate, aryl N‐aminosulfonamide, thus converting waste to chemical values. In situ X‐ray diffraction, infrared micro‐spectroscopy and inelastic neutron scattering enable the visualisation of the binding domains of adsorbed SO₂ molecules and host–guest binding dynamics in these materials at the atomic level. Refinement of the pore environment plays a critical role in designing efficient sorbent materials.

Adsorption of Sulfur Dioxide in Cu(II)-Carboxylate Framework Materials: The Role of Ligand Functionalization and Open Metal Sites

The development of efficient sorbent materials for sulfur dioxide (SO₂) is of key industrial interest. However, due to the corrosive nature of SO₂, conventional porous materials often exhibit poor reversibility and limited uptake toward SO₂ sorption. Here, we report high adsorption of SO₂ in a series of Cu(II)-carboxylate-based metal–organic framework materials. We describe the impact of ligand functionalization and open metal sites on the uptake and reversibility of SO₂ adsorption. Specifically, MFM-101 and MFM-190(F) show fully reversible SO₂ adsorption with remarkable capacities of 18.7 and 18.3 mmol g^–1, respectively, at 298 K and 1 bar; the former represents the highest reversible uptake of SO₂ under ambient conditions among all porous solids reported to date. In situ neutron powder diffraction and synchrotron infrared microspectroscopy enable the direct visualization of binding domains of adsorbed SO₂ molecules as well as host–guest binding dynamics. We have found that the combination of open Cu(II) sites and ligand functionalization, together with the size and geometry of metal–ligand cages, plays an integral role in the enhancement of SO₂ binding.

Degradable, antibacterial and ultrathin filtrating electrospinning membranes of Ag-MOFs/poly(l-lactide) for air pollution control and medical protection

The widely used melt-blown polypropylene (PP) non-woven fabrics had no antibacterial functions and its large-scale use also increased the burden on the environment owing to its non-degradable property. Herein, silver (I) metal organic frameworks (Ag-2MI) were prepared with AgNO3 and 2-methylimidazole and embedded into degradable poly(l-lactide) (PLLA) to make an ultrathin filtration and antibacterial membrane by electrospinning technology with low loading of Ag-2MI. The morphology, mechanical properties, adsorption performance and antibacterial activities of the prepared films were tested and the results indicated that the addition of Ag-2MI could reduce the diameter of PLLA fibers from 910 nm to 520 nm (1.8 wt% of Ag-2MI), while the tensile strength, elongation at break of the membrane and the contact angle of the films were enhanced. Although the thickness of the prepared membranes was only about one-third of that of commercially available melt-blown cloth, they exhibited better filtering performances than the melt-blown cloth. The fiber membrane with low loading of 1.8 wt% Ag-2MI showed 99.99% inhibition rate against Escherichia coli and Staphylococcus aureus.

U-Co Bimetallic-Organic Framework Showing a Helical 1D Pore Decorated by Abundant -CH3 Groups: Robust Nature under Acid, Base, and Water for High-Performance SO2 Removal

Constructing robust adsorbents for SO₂ removal remains a challenging issue. Herein, a U-Co bimetallic-organic framework, namely, ECUT-123, showing a helical 1D pore decorated by abundant -CH₃ groups, enables ultrahigh stability under acid, base, and water. This merit further supports its big potential for the removal of trace SO₂.

Capture and Separation of SO2 Traces in Metal-Organic Frameworks via Pre-Synthetic Pore Environment Tailoring by Methyl Groups

Herein, we report a pre-synthetic pore environment design strategy to achieve stable methyl-functionalized metal-organic frameworks (MOFs) for preferential SO2 binding and thus enhanced low (partial) pressure SO2 adsorption and SO2 /CO2 separation. The enhanced sorption performance is for the first time attributed to an optimal pore size by increasing methyl group densities at the benzenedicarboxylate linker in [Ni2 (BDC-X)2 DABCO] (BDC-X=mono-, di-, and tetramethyl-1,4-benzenedicarboxylate/terephthalate; DABCO=1,4-diazabicyclo[2,2,2]octane). Monte Carlo simulations and first-principles density functional theory (DFT) calculations demonstrate the key role of methyl groups within the pore surface on the preferential SO2 affinity over the parent MOF. The SO2 separation potential by methyl-functionalized MOFs has been validated by gas sorption isotherms, ideal adsorbed solution theory calculations, simulated and experimental breakthrough curves, and DFT calculations.

14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(iii) devoid of agostic interactions. The complexes [X-Rh(κ³(P,Si,Si)PhP(o-C₆H₄CH₂SiⁱPr₂)₂], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl₃ (Rh-5); derive from a bis(silyl)-o-tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl-Ir(κ³(P,Si,Si)PhP(o-C₆H₄CH₂SiⁱPr₂)₂], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et₃SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et₃SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M(iii) complexes.

Zirconium and Aluminum MOFs for Low-Pressure SO2 Adsorption and Potential Separation: Elucidating the Effect of Small Pores and NH2 Groups

Finding new adsorbents for the desulfurization of flue gases is a challenging task but is of current interest, as even low SO₂ emissions impair the environment and health. Four Zr- and eight Al-MOFs (Zr-Fum, DUT-67(Zr), NU-1000, MOF-808, Al-Fum, MIL-53(Al), NH₂-MIL-53(Al), MIL-53(tdc)(Al), CAU-10-H, MIL-96(Al), MIL-100(Al), NH₂-MIL-101(Al)) were examined toward their SO₂ sorption capability. Pore sizes in the range of about 4-8 Å are optimal for SO₂ uptake in the low-pressure range (up to 0.1 bar). Pore widths that are only slightly larger than the kinetic diameter of 4.1 Å of the SO₂ molecules allow for multi-side-dispersive interactions, which translate into high affinity at low pressure. Frameworks NH₂-MIL-53(Al) and NH₂-MIL-101(Al) with an NH₂-group at the linker tend to show enhanced SO₂ affinity. Moreover, from single-gas adsorption isotherms, ideal adsorbed solution theory (IAST) selectivities toward binary SO₂/CO₂ gas mixtures were determined with selectivity values between 35 and 53 at a molar fraction of 0.01 SO₂ (10.000 ppm) and 1 bar for the frameworks Zr-Fum, MOF-808, NH₂-MIL-53(Al), and Al-Fum. Stability tests with exposure to dry SO₂ during ≤10 h and humid SO₂ during 5 h showed full retention of crystallinity and porosity for Zr-Fum and DUT-67(Zr). However, NU-1000, MOF-808, Al-Fum, MIL-53(tdc), CAU-10-H, and MIL-100(Al) exhibited ≥50-90% retained Brunauer-Emmett-Teller (BET)-surface area and pore volume; while NH₂-MIL-100(Al) and MIL-96(Al) demonstrated a major loss of porosity under dry SO₂ and MIL-53(Al) and NH₂-MIL-53(Al) under humid SO₂. SO₂ binding sites were revealed by density functional theory (DFT) simulation calculations with adsorption energies of -40 to -50 kJ·mol^-1 for Zr-Fum and Al-Fum and even above -50 kJ·mol^-1 for NH₂-MIL-53(Al), in agreement with the isosteric heat of adsorption near zero coverage (ΔH_ads⁰). The predominant, highest binding energy noncovalent binding modes in both Zr-Fum and Al-Fum feature μ-OH^δ+···^δ-OSO hydrogen bonding interactions. The small pores of Al-Fum allow the interaction of two μ-OH bridges from opposite pore walls with the same SO₂ molecule via OH^δ+···^δ-OSO^δ-···^δ+HO hydrogen bonds. For NH₂-MIL-53(Al), the DFT high-energy binding sites involve NH^δ+···^δ-OS together with the also present Al-μ-OH^δ+···^δ-OS hydrogen bonding interactions and C₆-π^δ-···^δ+SO₂, N^δ-···^δ+SO₂ interactions.

Quantitative Structure-Activity Relationship of Nanowire Adsorption to SO2 Revealed by In Situ TEM Technique

A quantitative structure-activity relationship (QSAR) is revealed based on the real-time sulfurization processes of ZnO nanowires observed via gas-cell in situ transmission electron microscopy (in situ TEM). According to the in situ TEM observations, the ZnO nanowires with a diameter of 100 nm (ZnO-100 nm) gradually transform into a core-shell nanostructure under SO₂ atmosphere, and the shell formation kinetics are quantitatively determined. However, only sparse nanoparticles can be observed on the surface of the ZnO-500 nm sample, which implies a weak solid-gas interaction between SO₂ and ZnO-500 nm. The QSAR model is verified with heat of adsorption (-ΔH°) and aberration-corrected TEM characterization. With the guidance of the QSAR model, the following adsorbing/sensing applications of ZnO nanomaterials are explored: (i) breakthrough experiment demonstrates the application potential of the ZnO-100 nm sample for SO₂ capture/storage; (ii) the ZnO-500 nm sample features good reversibility (RSD = 1.5%, n = 3) for SO₂ sensing, and the detection limit reaches 70 ppb.

A Robust Cage-Based Metal-Organic Framework Showing Ultrahigh SO2 Uptake for Efficient Removal of Trace SO2 from SO2/CO2 and SO2/CO2/N2 Mixtures

Removal of trace SO₂ from an SO₂-containing product is now receiving increasing attention. However, designing a robust porous adsorbent with high SO₂ adsorption capacity and good SO₂/CO₂ selectivity, as well as validity under humid conditions, is still a challenging task. Herein, we report a porous cage-based metal-organic framework, namely ECUT-111, which contains two distinct cages with apertures of 5.4 and 10.2 Å, respectively, and shows high a BET of up to 1493 m²/g and a pore volume of 0.629 cm³/g. Impressively, ECUT-111 enables an ultrahigh SO₂ uptake of up to 11.56 mmol/g, exceeding most reported top-performing adsorbents for such a use. More importantly, complete separation of trace SO₂ from SO₂/CO₂ and SO₂/CO₂/N₂ mixtures, especially under humid conditions, and excellent recycle use were observed for ECUT-111, suggesting its superior application in desulfurization of SO₂-containing products.

SO2 capture enhancement in NU-1000 by the incorporation of a ruthenium gallate organometallic complex

[RuGa]@NU-1000 shows enhanced adsorption of SO2, specially at low pressures (10−3 bar) even when compared with other materials employing more expensive precious metals.

High Adsorption Capacity and Selectivity of SO2 over CO2 in a Metal-Organic Framework

Herein, we report a new metal-organic framework (MOF), namely, ECUT-77, which is built on rod-shaped secondary building units, showing a high Brunauer-Emmett-Teller surface area of 760.3 cm²/g, a pore volume of 0.4 cm³/g, and an aperture of about 1 nm. This MOF enables both high SO₂ adsorption capacity up to 8.0 mmol/g at 0.92 bar and room temperature and a high SO₂/CO₂ selectivity of 44, resulting in excellent SO₂ separation upon a ECUT-77 column from a SO₂/CO₂ mixture containing 2000 ppm of SO₂.