A Photosensitizing Metal–Organic Framework as a Tandem Reaction Catalyst for Primary Alcohols from Terminal Alkenes and Alkynes

Owing to the wide and growing demand for primary alcohols, the development of efficient catalysts with high regioselectivity remains a worthwhile pursuit. However, according to Markovnikov's rule, it is a challenge to obtain primary alcohols with high yields and regioselectivity from terminal alkenes or alkynes. Herein, we report the synthesis of a photosensitizing two-dimensional (2D) metal–organic framework (MOF) from cyclic trinuclear copper(I) units (Cu-CTUs) and a boron dipyrro-methene (Bodipy) ligand. The MOF features broadband light absorption, excellent photoinduced charge separation efficiency, and photochemical properties. By integrating the copper-catalyzed hydroboration and photocatalyzed aerobic oxidation, it can catalyze terminal alkenes and alkynes to produce primary alcohols via a one-pot tandem reaction with excellent regioselectivity, good overall yields in two-step reactions (up to 85 %), broad substrate compatibility (32 examples) and good reusability under mild conditions.     

A Titanium Metal–Organic Framework with Visible-Light-Responsive Photocatalytic Activity

The one-step synthesis and characterization of a new and robust titanium-based metal–organic framework, ACM-1 , is reported. In this structure, which is based on infinite Ti−O chains and 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl) tetrabenzoic acid as a photosensitizer ligand, the combination of highly mobile photogenerated electrons and a strong hole localization at the organic linker results in large charge-separation lifetimes. The suitable energies for band gap and conduction band minimum (CBM) offer great potential for a wide range of photocatalytic reactions, from hydrogen evolution to the selective oxidation of organic substrates.     

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.     

2D Metal–Organic Framework Nanosheets based on Pd-TCPP as Photocatalysts for Highly Improved Hydrogen Evolution

In this report, a 2D MOF nanosheet derived Pd single-atom catalyst, denoted as Pd-MOF, was fabricated and examined for visible light photocatalytic hydrogen evolution reaction (HER). This Pd-MOF can provide a remarkable photocatalytic activity (a H₂ production rate of 21.3 mmol/gh in the visible range), which outperforms recently reported Pt-MOFs (with a H₂ production rate of 6.6 mmol/gh) with a similar noble metal loading. Notably, this high efficiency of Pd-MOF is not due to different chemical environment of the metal center, nor by changes in the spectral light absorption. The higher performance of the Pd-MOF in comparison to the analogue Pt-MOF is attributed to the longer lifetime of the photogenerated electron-hole pairs and higher charge transfer efficiency.     

Amino-Induced 2D Cu-Based Metal–Organic Framework as an Efficient Heterogeneous Catalyst for Aerobic Oxidation of Olefins

With the assistance of hydrogen bonds of the o-amino group, we have successfully tuned a coordination structure from a metal–organic polyhedron (MOP) to a two-dimensional (2D) metal–organic framework (MOF). The amino group forms hydrogen bonds with the two vicinal carboxylic groups, and induces the ligand to coordinate with copper ions to form the 2D structure. The obtained 2D Cu-based MOF (Cu-AIA) has been applied as an efficient heterogeneous catalyst in the aerobic epoxidation of olefins by using air as oxygen source. Without the aggregation problem of active sites in MOPs, Cu-AIA possesses much higher reactivity than MOP-1. Furthermore, the amino group of the framework has been used as a modifiable site through post-synthetic metalation (PSMet) to prepare a 2D MOF-supported Pd single-site heterogeneous catalyst, which shows excellent catalytic performance for the Suzuki reaction. It indicates that Cu-AIA can also work as a good 2D MOF carrier for the derivation of other heterogeneous catalysts.     

A Porous Sulfonated 2D Zirconium Metal–Organic Framework as a Robust Platform for Proton Conduction

By using the strategy of pre-assembly chlorosulfonation applied to a linker precursor, the first sulfonated zirconium metal–organic framework ( JUK-14 ) with two-dimensional (2D) structure, was synthesized. Single-crystal X-ray diffraction reveals that the material is built of Zr₆O₄(OH)₄(COO)₈ oxoclusters, doubly 4-connected by angular dicarboxylates, and stacked in layers spaced 1.5 nm apart by the presence of sulfonic groups. JUK-14 exhibits excellent hydrothermal stability, permanent porosity confirmed by gas adsorption studies, and shows high (>10⁻⁴ S/cm) and low (<10⁻⁸ S/cm) proton conductivity under humidified and anhydrous conditions, respectively. Post-synthesis inclusion of imidazole improves the overall conductivity increasing it to 1.7×10⁻³ S/cm at 60 °C and 90 % relative humidity, and by 3 orders of magnitude at 160 °C. The combination of 2D porous nature with robustness of zirconium MOFs offers new opportunities for exploration of the material towards energy and environmental applications.     

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface-Mounted Metal–Organic Frameworks

Metal–organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a “strain modulation” approach has been applied through the use of surface-mounted NiFe-MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm⁻² at an overpotential of only ≈210 mV. It demonstrates operational long-term stability even at a high current density of 500 mA cm⁻² and exhibits the so far narrowest “overpotential window” ΔE_ORR-OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.     

Polymeric Donor–Acceptor Heterostructures for Enhanced Photocatalytic H2 Evolution without Using Pt Cocatalysts

Polymeric carbon nitride (CN) is a promising material for photocatalytic water splitting. However, CN in its pristine form tends to show moderate activity due to fast recombination of the charge carriers. The design of efficient photocatalytic system is therefore highly desired, but it still remains a great challenge in chemistry. In this work, a pyrene-based polymer able to serve as an electron donor to accelerate the interface charge carrier transfer of CN is presented. The construction of donor-acceptor (D–A) heterojunction was confirmed to significantly restrain the charge recombination and, thus, improve the proton reduction process. This study provides a promising strategy to achieve solar H₂ production in an efficient and low-cost manner.     

A Hydrogen-Deficient Nickel–Cobalt Double Hydroxide for Photocatalytic Overall Water Splitting

Developing highly efficient and low-cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble-metal co-catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so-called L-NiCo nanosheets with a nonstoichiometric composition and O²⁻/Co³⁺ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O²⁻ and Co³⁺ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H₂ evolution rate of 1.7 μmol h⁻¹ under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm.     

Defect Engineered Metal–Organic Framework with Accelerated Structural Transformation for Efficient Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) have been increasingly applied in oxygen evolution reaction (OER), and the surface of MOFs usually undergoes structural transformation to form metal oxyhydroxides to serve as catalytically active sites. However, the controllable regulation of the reconstruction process of MOFs remains as a great challenge. Here we report a defect engineering strategy to facilitate the structural transformation of MOFs to metal oxyhydroxides during OER with enhanced activity. Defective MOFs (denoted as NiFc′_xFc_1-x) with abundant unsaturated metal sites are constructed by mixing ligands of 1,1′-ferrocene dicarboxylic acid (Fc′) and defective ferrocene carboxylic acid (Fc). NiFc′_xFc_1-x series are more prone to be transformed to metal oxyhydroxides compared with the non-defective MOFs (NiFc′). Moreover, the as-formed metal oxyhydroxides derived from defective MOFs contain more oxygen vacancies. NiFc′Fc grown on nickel foam exhibits excellent OER catalytic activity with an overpotential of 213 mV at the current density of 100 mA cm⁻², superior to that of undefective NiFc′. Experimental results and theoretical calculations suggest that the abundant oxygen vacancies in the derived metal oxyhydroxides facilitate the adsorption of oxygen-containing intermediates on active centers, thus significantly improving the OER activity.     

A Hydrolytically Stable Vanadium(IV) Metal–Organic Framework with Photocatalytic Bacteriostatic Activity for Autonomous Indoor Humidity Control

Metal–organic frameworks (MOFs) with long-term stability and reversible high water uptake properties can be ideal candidates for water harvesting and indoor humidity control. Now, a mesoporous and highly stable MOF, BIT-66 is presented that has indoor humidity control capability and a photocatalytic bacteriostatic effect. BIT-66 (V₃(O)₃(H₂O)(BTB)₂), possesses prominent moisture tunability in the range of 45–60 % RH and a water uptake and working capacity of 71 and 55 wt %, respectively, showing good recyclability and excellent performance in water adsorption–desorption cycles. Importantly, this MOF demonstrates a unique photocatalytic bacteriostatic behavior under visible light, which can effectively ameliorate the bacteria and/or mold breeding problem in water adsorbing materials.     

A New Biscarbazole-Based Metal–Organic Framework for Efficient Host–Guest Energy Transfer

A new metal–organic framework (MOF), [Zn₆L₄(Me₂NH₂⁺)₄⋅3 H₂O] ( 1 ) was constructed based on [9, 9′-biscarbazole]-3, 3′, 6, 6′-tetracarboxylic acid (H₄L) and Zn²⁺ ions. The porous framework and intense blue fluorescence of the MOF based on the biscarbazole moiety of the ligand could facilitate efficient host to guest energy transfer, which makes it an ideal platform for the tuning of luminescence.     

Metal–Organic Framework (MOF)-Based Materials as Heterogeneous Catalysts for C−H Bond Activation

Converting light hydrocarbons such as methane, ethane, propane, and cyclohexane into value-added chemicals and fuel products by means of direct C−H functionalization is an attractive method in the petrochemical industry. As they emerge as a relatively new class of porous solid materials, metal–organic frameworks (MOFs) are appealing as single-site heterogeneous catalysts or catalytic supports for C−H bond activation. In contrast to the traditional microporous and mesoporous materials, MOFs feature high porosity, functional tunability, and molecular-level characterization for the study of structure–property relationships. These virtues make MOFs ideal platforms to develop catalysts for C−H activation with high catalytic activity, selectivity, and recyclability under relatively mild reaction conditions. This review highlights the research aimed at the implementation of MOFs as single-site heterogeneous catalysts for C−H bond activation. It provides insight into the rational design and synthesis of three types of stable MOF catalysts for C−H bond activation, that is, i) metal nodes as catalytic sites, ii) the incorporation of catalytic sites into organic struts, and iii) the incorporation of catalytically active guest species into pores of MOFs. Here, the rational design and synthesis of MOF catalysts that lead to the distinct catalytic property for C−H bond activation are discussed along with the post-synthesis of MOFs, intriguing functions with MOF catalysts, and microenvironments that lead to the distinct catalytic properties of MOF catalysts.     

Zr-Porphyrin Metal–Organic Framework as nanoreactor for boosting the formation of hydrogen clathrates

We report the first experimental evidence for rapid formation of hydrogen clathrates under mild pressure and temperature conditions within the cavities of a zirconium-metalloporphyrin framework, specifically PCN-222. PCN-222 has been selected for its 1D mesoporous channels, high water-stability, and proper hydrophilic behavior. Firstly, we optimize a microwave (MW)-assisted method for the synthesis of nanosized PCN-222 particles with precise structure control (exceptional homogeneity in morphology and crystalline phase purity), taking advantage of MW in terms of rapid/homogeneous heating, time and energy savings, as well as potential scalability of the synthetic method. Second, we explore the relevance of the large mesoporous 1D open channels within the PCN-222 to promote the nucleation and growth of confined hydrogen clathrates. Experimental results show that PCN-222 drives the nucleation process at a lower pressure than the bulk system (1.35 kbar vs 2 kbar), with fast kinetics (minutes), using pure water, and with a nearly complete water-to-hydrate conversion. Unfortunately, PCN-222 cannot withstand these high pressures, which lead to a significant alteration of the mesoporous structure while the microporous network remains mainly unchanged.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi-M′MOF , pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm⁻³, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂-capture amount of 4.54 mol L⁻¹, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi-M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M′MOF as a promising material for C₂H₂/CO₂ separation.     

Construction of Asymmetrical Dual Jahn–Teller Sites for Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction (PCR) expresses great attraction to convert useless greenhouse gas into valuable chemical feedstock. However, the weak interactions between catalytic sites and PCR intermediates constrains the PCR activity and selectivity. Herein, we proposed a new strategy to match the intermediates due to the maximum orbital overlap of catalytic sites and C₁ intermediates by establishing dual Jahn–Teller (J–T) sites, in which, the strongly asymmetric J–T sites can break the nonpolar CO₂ molecules and self-adapt the different structure of C₁ intermediates. Taking cobalt carbonate hydroxide as an example, the weakly symmetric dual cobalt (Co₂) dual J–T sites, weakly asymmetric Fe&Co sites and strongly asymmetric Cu&Co sites were assembled. After illumination, the interaction between dual J–T sites and the CO₂ molecules enhances J–T distortion, which further modulates the PCR activity and selectivity. As a result, the Cu&Co sites exhibited CO yield of 8137.9 μmol g⁻¹, about 2.3-fold and 4.2-fold higher than that of the Fe&Co and Co₂ sites within 5-hour photoreaction, respectively. In addition, the selectivity achieved as high as 92.62 % than Fe&Co (88.67 %) and Co₂ sites (55.33 %). This work provides a novel design concept for the construction of dual J–T sites to regulate the catalytic activity and selectivity.     

A Redox-Active 2D Metal–Organic Framework for Efficient Lithium Storage with Extraordinary High Capacity

Metal–organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li-ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox-active 2D copper–benzoquinoid (Cu-THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu-THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li-ion battery cathode with a high reversible capacity (387 mA h g⁻¹), large specific energy density (775 Wh kg⁻¹), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three-electron redox reaction per coordination unit and one-electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high-performance MOF-based cathode materials for efficient energy storage and conversion.     

Ionic Liquid as Catalyst and Reaction Medium: A Simple and Efficient Procedure for Paal–Knorr Furan Synthesis

The ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulfate, [bmim]HSO₄, efficiently catalyzes Paal–Knorr furan synthesis without any organic solvent. A wide range of aliphatic and aromatic 1,4-diketones easily undergo condensations to form furan derivatives, providing a general and convenient procedure. The Paal–Knorr reaction of ester-substituted 1,4-diketones is first reported. The ionic liquid can be recovered and reused for subsequent runs without any appreciable loss of efficiency.