Two-Dimensional Metal–Organic Framework Nanosheets with Cobalt-Porphyrins for High-Performance CO2 Electroreduction

The electrochemical reduction of CO₂ presents a promising strategy to mitigate the greenhouse effect and reduce excess carbon dioxide emission to realize a carbon-neutral energy cycle, but it suffers from the lack of high-performance electrocatalysts. In this work, catalytic active cobalt porphyrin [TCPP(Co)=(5,10,15,20)-tetrakis(4-carboxyphenyl)porphyrin-Co^II] was precisely anchored onto water-stable 2D metal–organic framework (MOF) nanosheets (Zr-BTB) to obtain ultrathin 2D MOF nanosheets [TCPP(Co)/Zr-BTB] with accessible catalytic sites for the CO₂ reduction reaction. Compared with molecular cobalt porphyrin, the TCPP(Co)/Zr-BTB exhibits an ultrahigh turnover frequency (TOF=4768 h⁻¹ at −0.919 V vs. reversible hydrogen electrode, RHE) owing to high active-site utilization. In addition, three post-modified 2D MOF nanosheets [TCPP(Co)/Zr-BTB-PABA, TCPP(Co)/Zr-BTB-PSBA, TCPP(Co)/Zr-BTB-PSABA] were obtained, with the modifiers of p-(aminomethyl)benzoic acid (PABA), p-sulfobenzoic acid potassium (PSBA), and p-sulfamidobenzoic acid (PSABA), to change the micro-environments around TCPP(Co) through the tuning of steric effects. Among them, the TCPP(Co)/Zr-BTB-PSABA exhibited the best performance with a faradaic efficiency (FE_CO) of 85.1 %, TOF of 5315 h⁻¹, and j_total of 6 mA cm⁻² at −0.769 V (vs. RHE). In addition, the long-term durability of the electrocatalysts is evaluated and the role of pH buffer is revealed.     

Simultaneous Capture of CO2 Boosting Its Electroreduction in the Micropores of a Metal–organic Framework

Integration of CO₂ capture capability from simulated flue gas and electrochemical CO₂ reduction reaction (eCO₂RR) active sites into a catalyst is a promising cost-effective strategy for carbon neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO₂RR tests, we showed that an Ag₁₂ cluster-based metal–organic framework ( 1-NH₂ , aka Ag₁₂bpy-NH₂ ), simultaneously possessing CO₂ capture sites as “CO₂ relays” and eCO₂RR active sites, can not only utilize its micropores to efficiently capture CO₂ from simulated flue gas (CO₂ : N₂=15 : 85, at 298 K), but also catalyze eCO₂RR of the adsorbed CO₂ into CO with an ultra-high CO₂ conversion of 60 %. More importantly, its eCO₂RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm⁻² at a very low cell voltage of −2.3 V for 300 hours and the full-cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO₂ atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO₂ atmosphere. This work bridges the gap between CO₂ enrichment/capture and eCO₂RR.     

Transformation of an Imine Cage to a Covalent Organic Framework Film at the Liquid–Liquid Interface

Dynamic covalent chemistry (DCC) opens up a fascinating route for the construction of well-organized supramolecular architectures, starting from organic molecular cages to crystalline macromolecular covalent organic frameworks (COFs). Herein, for the first time, we have manifested a facile room-temperature DCC-directed transformation of discrete organic imine cage-to-COF film at the liquid–liquid interface. The unfolding of the cage leading to the generation of imine intermediates, followed by their interface-assisted preorganization and subsequent growth of the COF film, are elucidated through detailed spectroscopic and microscopic investigations. The interfacial cage-to-COF transformation provides a facile route for the faster fabrication of free-standing COF films with high porosity and crystallinity, demonstrating excellent performance towards molecular sieving and high solvent permeance. Thus, the current study opens up a new route for structural interconversion between two crystalline entities with diverse dimensionality employing DCC at the confined interface.     

Incarceration of Iodine in a Pyrene-Based Metal–Organic Framework

A pyrene-based metal-organic framework (MOF) SION-8 captured iodine (I₂) vapor with a capacity of 460 and 250 mg g⁻¹_MOF at room temperature and 75 °C, respectively. Single-crystal X-ray diffraction analysis and van-der-Waals-corrected density functional theory calculations confirmed the presence of I₂ molecules within the pores of SION-8 and their interaction with the pyrene-based ligands. The I₂–pyrene interactions in the I₂-loaded SION-8 led to a 10⁴-fold increase of its electrical conductivity compared to the bare SION-8 . Upon adsorption, ≥95 % of I₂ molecules were incarcerated and could not be washed out, signifying the potential of SION-8 towards the permanent capture of radioactive I₂ at room temperature.     

Encapsulation of a Porous Organic Cage into the Pores of a Metal–Organic Framework for Enhanced CO2 Separation

We present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient-wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO₂ affinity were successfully encapsulated into the nanospace of Cr-based MIL-101 while retaining the crystal framework, morphology, and high stability of MIL-101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL-101, more affinity sites for CO₂ are created in the resulting CB6@MIL-101 composites, leading to enhanced CO₂ uptake capacity and CO₂/N₂, CO₂/CH₄ separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications.     

Facilitated Photocatalytic CO2 Reduction in Aerobic Environment on a Copper-Porphyrin Metal–Organic Framework

Herein, we fabricated a π–π stacking hybrid photocatalyst by combining two two-dimensional (2D) materials: g-C₃N₄ and a Cu-porphyrin metal–organic framework (MOF). After an aerobic photocatalytic pretreatment, this hybrid catalyst exhibited an unprecedented ability to photocatalytically reduce CO₂ to CO and CH₄ under the typical level (20 %) of O₂ in the air. Intriguingly, the presence of O₂ did not suppress CO₂ reduction; instead, a fivefold increase compared with that in the absence of O₂ was observed. Structural analysis indicated that during aerobic pretreatment, the Cu node in the 2D-MOF moiety was hydroxylated by the hydroxyl generated from the reduction of O₂. Then the formed hydroxylated Cu node maintained its structure during aerobic CO₂ reduction, whereas it underwent structural alteration and was reductively devitalized in the absence of O₂. Theoretical calculations further demonstrated that CO₂ reduction, instead of O₂ reduction, occurred preferentially on the hydroxylated Cu node.     

Evidence of a Uranium-Paddlewheel Node in a Catecholate-Based Metal–Organic Framework

The interactions between uranium and non-innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium-based metal–organic frameworks (MOFs) offer a new angle to study these interactions, as these self-assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non-innocent linkers. We report the synthesis of the MOF NU-1700 , assembled from U⁴⁺-paddlewheel nodes and catecholate-based linkers. We propose this highly unusual structure, which contains two U⁴⁺ ions in a paddlewheel built from four linkers—a first among uranium materials—as a result of extensive characterization via powder X-ray diffraction (PXRD), sorption, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA), in addition to density functional theory (DFT) calculations.     

Thermal Elimination of Ethylene from Cyclobutyl Groups Characterized by X-ray Crystallography in a Metal–Organic Framework Matrix

Methods to synthesize and characterize aromatic molecules with vinyl substituents are sought after yet limited in the literature. Here, we introduce cyclobutyl groups into a metal–organic framework (MOF) matrix that are poised to produce ethylene upon heating. The expulsion of ethylene produces vinyl groups on an aromatic core, which are isolated by the crystalline matrix of the framework. This enables full characterization of the thermolysis by single-crystal X-ray diffraction. Further, we modify the vinyl groups by a bromine addition reaction. Importantly, the two transformations happen in a single-crystal-to-single-crystal manner without changing the overall network structure of the parent framework. New insights into the structural and synthetic chemistry of this important class of compound are generated. Installing reactive vinyl tags in materials by the high temperature thermolysis of cyclobutyl groups is a powerful strategy for altering their physicochemical characteristics.     

Enhancing CO2 Electroreduction to Methane with a Cobalt Phthalocyanine and Zinc–Nitrogen–Carbon Tandem Catalyst

Developing copper-free catalysts for CO₂ conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO₂ reduction reaction (CO₂RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc–nitrogen–carbon (Zn-N-C) tandem catalyst for CO₂RR to CH₄. This tandem catalyst shows a more than 100 times enhancement of the CH₄/CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO₂ is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH₄ over Zn-N₄ site, decoupling complicated CO₂RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N₄, which is the key to achieve the high CH₄ production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.     

Reversible Postsynthetic Modification in a Metal–Organic Framework

Postsynthetic modification (PSM) of metal–organic frameworks (MOFs) provides access to functional materials and advanced porous solid engineering. Herein, we report the reversible PSM of a multivariate isoreticular MOF by applying dynamic furan-maleimide Diels–Alder (DA) chemistry. The key step involves incorporating a furan group into the MOF via “click” PSM, which can then undergo repeated cycles of modification and de-modification with maleimides. The structural integrity, crystallinity, and porosity of the furan-appended MOF remained intact even after three consecutive PSM/de-modification cycles using three different functionalized maleimides.     

Fast Detection of Entacapone by a Lanthanide–Organic Framework with Rhombic Channels

Entacapone (ENT) is a powerful catechol-O-methyl transferase inhibitor that is used for the diagnosis and treatment of Parkinson's syndrome, but the amount used must be well controlled to avoid overtreatment and side effect. Fast and selective detection of ENT needs well-matched energy levels and well-designed sensor-ENT interaction which is highly challenging. In this work, a water stable europium-based metal-organic framework ( Eu-TDA ) was synthesized to detect ENT by luminescence with excellent reusability and selectivity in the presence of main coexisting and interference species of plasma with a limit of detection of 5.01 μM. The experimental results showed that the luminescence of Eu-TDA can be effectively quenched by ENT via well-designed photoinduced electron transfer mechanism and internal filtration effect mechanism in the system.     

Ambient Chemical Fixation of CO2 Using a Robust Ag27 Cluster-Based Two-Dimensional Metal–Organic Framework

Unprecedented double S²⁻ templated Ag₂₇ clusters have been stabilized by 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP-H₂) ligands to afford a robust 2D metal–organic framework ( Ag27-MOF ). This silver cluster-assembled material serves as a highly efficient heterogeneous catalyst for the cyclization of both terminal and internal propargylamines with CO₂ under atmospheric pressure. Density functional theory (DFT) calculations illustrate that the high catalytic activity and broad substrate scope are attributable to the saddle-shaped metallic node in Ag27-MOF , which features an accessible platform with high-density silver atoms as π-Lewis acid sites for activating C≡C triple bonds. As a result, different sterically hindered alkyne substrates can be effectively activated through π-interactions with these cationic silver centers.     

Coordination-Induced Band Gap Reduction in a Metal–Organic Framework

Herein, we report on the synthesis of a microporous, three-dimensional phosphonate metal–organic framework (MOF) with the composition Cu₃(H₅-MTPPA)₂ ⋅ 2 NMP (H₈-MTPPA=methane tetra-p-phenylphosphonic acid and NMP=N-methyl-2-pyrrolidone). This MOF, termed TUB1, has a unique one-dimensional inorganic building unit composed of square planar and distorted trigonal bipyramidal copper atoms. It possesses a (calculated) BET surface area of 766.2 m²/g after removal of the solvents from the voids. The Tauc plot for TUB1 yields indirect and direct band gaps of 2.4 eV and 2.7 eV, respectively. DFT calculations reveal the existence of two spin-dependent gaps of 2.60 eV and 0.48 eV for the alpha and beta spins, respectively, with the lowest unoccupied crystal orbital for both gaps predominantly residing on the square planar copper atoms. The projected density of states suggests that the presence of the square planar copper atoms reduces the overall band gap of TUB1, as the beta-gap for the trigonal bipyramidal copper atoms is 3.72 eV.     

Ultrathin 2D Covalent Organic Framework Film Fabricated via Langmuir-Blodgett Method with a “Two-in-One” Type Monomer

In recent years, covalent organic frameworks(COFs) are evolving as a novel kind of porous materials for catalysis and molecular separation, gas adsorption, etc. Various functional building blocks have been explored to tune the pore channels, including the pore size and structures. In this article, a new terphenyl(TP) based COF(TP-COF) was developed via a “two-in-one” strategy by using a symmetric A₂B₂monomer, i.e., 4,4'-diamino-2',5'-diformyl-1,1':4',1'-terphenyl(DADFTP). The pore size of TP-COF was only 0.99 nm by shortening the arm length of the DADFTP monomer. Freestanding, continuous and ultrathin COF films could be facilely prepared at the air-liquid interface through the modified Langmuir-Blodgett(LB) method. TP-COF films exhibited high rejection of over 90% for dyes removal.     

Stabilizing DNAzymes through Encapsulation in a Metal–Organic Framework

DNAzymes are a promising class of bioinspired catalyst; however, their structural instability limits their potential. Herein, a method to stabilize DNAzymes by encapsulating them in a metal–organic framework (MOF) host is reported. This biomimetic mineralization process makes DNAzymes active under a wider range of conditions. The concept is demonstrated by encapsulating hemin-G-quadruplex (Hemin-G4) into zeolitic imidazolate framework-90 (ZIF-90), which indeed increases the DNAzyme's structural stability. The stabilized DNAzymes show activities in the presence of Exonuclease I, organic solvents, or high temperature. Owing to its elevated stability and heterogeneous nature, it is possible to perform catalysis under continuous-flow conditions, and the DNAzyme can be reactivated in situ by introducing K⁺. Moreover, it is found that the encapsulated DNAzyme maintains its high enantiomer selectivity, demonstrated by the sulfoxidation of thioanisole to (S)-methyl phenyl sulfoxide. This concept of stabilizing DNAzymes expands their potential application in chemical industry.     

Solid State Machinery of Multiple Dynamic Elements in a Metal–Organic Framework

Engineering coordinated rotational motion in porous architectures enables the fabrication of molecular machines in solids. A flexible two-fold interpenetrated pillared Metal-Organic Framework precisely organizes fast mobile elements such as bicyclopentane (BCP) (10⁷ Hz regime at 85 K), two distinct pyridyl rotors and E-azo group involved in pedal-like motion. Reciprocal sliding of the two sub-networks, switched by chemical stimuli, modulated the sizes of the channels and finally the overall dynamical machinery. Actually, iodine-vapor adsorption drives a dramatic structural rearrangement, displacing the two distinct subnets in a concerted piston-like motion. Unconventionally, BCP mobility increases, exploring ultra-fast dynamics (10⁷ Hz) at temperatures as low as 44 K, while the pyridyl rotors diverge into a faster and slower dynamical regime by symmetry lowering. Indeed, one pillar ring gained greater rotary freedom as carried by the azo-group in a crank-like motion. A peculiar behavior was stimulated by pressurized CO_2, which regulates BCP dynamics upon incremental site occupation. The rotary dynamics is intrinsically coupled to the framework flexibility as demonstrated by complementary experimental evidence (multinuclear solid-state NMR down to very low temperatures, synchrotron radiation XRD, gas sorption) and computational modelling, which helps elucidate the highly sophisticated rotor-structure interplay.     

Ferroelectric Metal–Organic Framework as a Host Material for Sulfur to Alleviate the Shuttle Effect of Lithium–Sulfur Battery

Ferroelectricity has an excellent reversible polarization conversion behavior under an external electric field. Herein, we propose an interesting strategy to alleviate the shuttle effect of lithium–sulfur battery by utilizing ferroelectric metal–organic framework (FMOF) as a host material for the first time. Compared to other MOF with same structure but without ferroelectricity and commercial carbon black, the cathode based on FMOF exhibits a low capacity decay and high cycling stability. These results demonstrate that the polarization switching behaviors of FMOF under the discharge voltage of lithium–sulfur battery can effectively trap polysulfides by polar–polar interactions, decrease polysulfides shuttle and improve the electrochemical performance of lithium–sulfur battery.     

Design of a Single-Atom Indiumδ+–N4 Interface for Efficient Electroreduction of CO2 to Formate

Main-group element indium (In) is a promising electrocatalyst which triggers CO₂ reduction to formate, while the high overpotential and low Faradaic efficiency (FE) hinder its practical application. Herein, we rationally design a new In single-atom catalyst containing exclusive isolated In^δ+–N₄ atomic interface sites for CO₂ electroreduction to formate with high efficiency. This catalyst exhibits an extremely large turnover frequency (TOF) up to 12500 h⁻¹ at −0.95 V versus the reversible hydrogen electrode (RHE), with a FE for formate of 96 % and current density of 8.87 mA cm⁻² at low potential of −0.65 V versus RHE. Our findings present a feasible strategy for the accurate regulation of main-group indium catalysts for CO₂ reduction at atomic scale.     

High Ammonia Uptake of a Metal–Organic Framework Adsorbent in a Wide Pressure Range

Although numerous porous adsorbents have been investigated for NH₃ capture applications, these materials often exhibit insufficient NH₃ uptake, low NH₃ affinity at the ppm level, and poor chemical stability against wet NH₃ conditions. The NH₃ capture properties of M₂(dobpdc) complexes (M=Mg²⁺, Mn²⁺, Co²⁺, Ni²⁺, and Zn²⁺; dobpdc⁴⁻=4,4-dioxidobiphenyl-3,3-dicarboxylate) that contain open metal sites is presented. The NH₃ uptake of Mg₂(dobpdc) at 298 K was 23.9 mmol g⁻¹ at 1 bar and 8.25 mmol g⁻¹ at 570 ppm, which are record high capacities at both pressures among existing porous adsorbents. The structural stability of Mg₂(dobpdc) upon exposure to wet NH₃ was superior to that of the other M₂(dobpdc) and the frameworks tested. Overall, these results demonstrate that Mg₂(dobpdc) is a recyclable compound that exhibits significant NH₃ affinity and capacity, making it a promising candidate for real-world NH₃-capture applications.