Metal–organic framework-derived porous materials for catalysis

Nanocasting SiO2 into metal-organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts

Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO₂ into porphyrinic metal-organic frameworks (MOFs). The pyrolysis of SiO₂@MOF composite affords single-atom Fe implanted N-doped porous carbon (Fe_SA-N-C) with high Fe loading (3.46 wt%). The spatial isolation of Fe atoms centered in porphyrin linkers of MOF sets the first protective barrier to inhibit the Fe agglomeration during pyrolysis. The SiO₂ in MOF provides additional protection by creating thermally stable FeN₄/SiO₂ interfaces. Thanks to the high-density Fe_SA sites, Fe_SA-N-C demonstrates excellent oxygen reduction performance in both alkaline and acidic medias. Meanwhile, Fe_SA-N-C also exhibits encouraging performance in proton exchange membrane fuel cell, demonstrating great potential for practical application. More far-reaching, this work grants a general synthetic methodology toward high-content SACs (such as Fe_SA, Co_SA, Ni_SA).

Transitional MOFs: Exposing Metal Sites with Porosity for Enhancing Catalytic Reaction Performance

The exploration of transitional metal-organic frameworks (MOFs) is important because of their unique properties and promising applications. Hence, finding a suitable strategy to design transitional MOFs with different states has become a key issue. Herein, we develop a modulator-induced strategy for fabricating transitional MOFs with carboxylic ligands by building esterification reaction. The exposed metal sites, mesoporous systems, morphologies, crystallinities, and components of transitional MOFs can be finely controlled when different modulators are employed. Notably, the Pt/solid-transitional MOF catalyst with more mesopores enhances conversion in the hydrogenation reaction of n-hexene, and the flower-like-transitional MOF catalyst with more Lewis acid sites exhibits better performance in the cycloaddition reaction. Therefore, the modulator-induced strategy may provide significant inspiration for preparing various transitional MOFs by building suitable chemical reactions.

Ni/Co bimetallic organic framework nanosheet assemblies for high-performance electrochemical energy storage

Nickel-cobalt organic framework (denoted as NiCo-MOF) nanosheet assemblies are prepared through a controllable one-pot hydrothermal synthesis procedure at 150 °C. The as-prepared samples are directly employed as electrode materials for electrochemical energy storage (EES), and exhibit excellent electrochemical performance. Among these samples, NiCo-MOF-1 displays a high capacity of 100.18 mA h g-1 (901.60 F g-1), and obtains a capacity retention of 81.00% over 3000 cycles at 5 A g-1. Likewise, in an aqueous device, NiCo-MOF-1//AC delivers a discharge capacity of 83.75 mA h g-1, and also exhibits a good cycling life (74.14% retention after 3000 cycles). These results demonstrate that multilayer NiCo-MOF nanosheet assemblies are potential electrode materials for EES.

Adsorptive removal of bulky dye molecules from water with mesoporous polyaniline-derived carbon

Polyaniline-derived carbon (PDC) was obtained via pyrolysis of polyaniline under different temperatures and applied for the purification of water contaminated with dye molecules of different sizes and charge by adsorption. With increasing pyrolysis temperature, it was found that the hydrophobicity, pore size and mesopore volume increased. A mesoporous PDC sample obtained via pyrolysis at 900 °C showed remarkable performance in the adsorption of dye molecules, irrespective of dye charge, especially in the removal of bulky dye molecules, such as acid red 1 (AR1) and Janus green B (JGB). For example, the most competitive PDC material showed a Q ₀ value (maximum adsorption capacity) 8.1 times that of commercial, activated carbon for AR1. The remarkable adsorption of AR1 and JGB over KOH-900 could be explained by the combined mechanisms of hydrophobic, π-π, electrostatic and van der Waals interactions.

Adsorption behavior and mechanism of arsenic on mesoporous silica modified by iron-manganese binary oxide (FeMnOx/SBA-15) from aqueous systems

Iron-manganese binary oxides (FeMnO_x) can remove contaminants from aqueous solutions with high efficiency, and mesoporous silica (SBA-15) is widely used as a supporting material due to its large specific surface area and good stability. In this study, SBA-15 was used to support FeMnO_x in the synthesis of a novel arsenic (As) adsorbent (FeMnO_x/SBA-15), and its characteristics under different reaction conditions, such as pH, temperature, presence of competing ions, and humic acid, were tested. The results showed that the contaminant adsorption efficiency of the novel adsorbent was better than that of bare FeMnO_x, as the addition of SBA-15 decreased the agglomeration effect of FeMnO_x. Additionally, FeMnO_x/SBA-15 underwent calcination to further enhance its performance. The state of iron and manganese in FeMnO_x/SBA-15 and the corresponding arsenic removal efficiency were improved by calcination at 350 °C with an FeMnO_x/SBA-15 mass fraction of approximately 45%. Almost 90% of As (50 mL, 5.0 mg L^-1) could be removed by 0.2 g L^-1 of FeMnO_x/SBA-15 (mass ratio of 45% and calcination temperature of 350 °C). The FeMnO_x/SBA-15 could regenerate and still be used after four consecutive cycles. The high As sorption capacity, ability to regenerate, and reusability of FeMnO_x/SBA-15 confirmed that this adsorbent is promising for treating As-contaminated drinking water.

Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co₃O₄ hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal-organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths-namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites-were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = -1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co₃O₄, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic performance in toluene oxidation, it achieved a toluene conversion of 90% (T₉₀) at ∼227 °C (a space velocity of 60 000 mL g^-1 h^-1) and the activity energy (E_a) is 69.5 kJ mol^-1. A series of characterizations were performed to investigate the structure-activity correlation. It was found that there are more structure defects, more adsorbed surface oxygen species, more surface Co³⁺ species, and higher reducibility at low temperatures on the Co-MeCN-O than on other Co₃O₄ samples; these factors are responsible for its excellent catalytic performance. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that, when there is no oxygen in the atmosphere, the lattice oxygen may be involved in the activation of toluene, and the gas-phase oxygen replenished by the oxygen vacancies was essential for the total oxidation of toluene on the surface of the Co-MeCN-O catalysts, it also proves the importance of oxygen vacancies. Moreover, for the Co-MeCN-O catalysts, no obvious decrease in catalytic performance was observed after 120 h at 220 °C and it is still stable after cycling tests, which indicates that it exhibits excellent stability for toluene oxidation. This study sheds lights on the controllable synthesis of macroporous-microporous materials in single-crystalline form without an external template, and, thus, it may serve as a reference for future design and synthesis of hollow porous materials with outstanding catalytic performance.

MIL-100(Fe) and its derivatives: from synthesis to application for wastewater decontamination

MIL-100(Fe), an environmental-friendly and water-stable metal-organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications. Graphical abstract.

Zirconium Oxide Sulfate-Carbon (ZrOSO4@C) Derived from Carbonized UiO-66 for Selective Production of Dimethyl Ether

Methanol dehydration process to dimethyl ether (DME) has been considered as one of the main routes to produce clean fuel, that is, DME. Thus, efficient catalysts are highly required for selective production of DME. Herein, UiO-66 was used as a precursor for the synthesis of zirconium oxide sulfate embedded carbon (ZrOSO₄@C). The synthesis method involves a one-step carbonization of UiO-66 in the presence of sulfuric acid (10 wt %). Material characterizations using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, and Raman spectroscopy approve the formation of the high crystalline phase of ZrOSO₄@C. Nitrogen adsorption-desorption isotherms and high-resolution transmission electron microscopy confirm the mesopore structure of the materials. Acidity analysis using pyridine temperature-programmed desorption and isopropanol dehydration corroborates that ZrOSO₄@C has weak and intermediate acidic sites making ZrOSO₄@C an effective catalyst for methanol dehydration to DME. The materials offered full conversion (100%) with excellent selectivity (100%) at a relatively low temperature (250 °C). The catalyst exhibited a long-term stability for 120 h. Based on these results, DME is produced efficiently in terms of conversion, selectivity, and long-term stability.

A novel cobalt doped MOF-based photocatalyst with great applicability as an efficient mediator of peroxydisulfate activation for enhanced degradation of organic pollutants

A novel cobalt doped MOF-based photocatalyst was synthesized for the first time and employed as a mediator of peroxydisulfate activation for enhanced pollutant degradation.

High rejection performance ultrafiltration membrane with ultrathin dense layer fabricated by the movement and dissolution of metal–organic frameworks

Ultrafiltration membranes have potential to solve the problems of water pollution and shortage.

Highly stable 3D porous HMOF with enhanced catalysis and fine color regulation by the combination of d- and p-ions when compared with those of its monometallic MOFs

Three comparable MOFs were yielded successfully. Among them, the highly stable HMOF is a porous 3D motif with lots of active sites, leading to the enhanced catalysis for CO₂ conversion and fine color regulations of MOFs by doping different ions.

Recent progress in pyrolyzed carbon materials as electrocatalysts for the oxygen reduction reaction

This review reports some recent advances in pyrolytic carbon as an ORR catalyst and explores its structure–activity relationship.

A comparative study between Cu(INA)2-MOF and [Cu(INA)2(H2O)4] complex for a click reaction and the Biginelli reaction under solvent-free conditions

The catalytic activity of metal–organic framework Cu(INA)₂ (INA = isonicotinate ion) and the complex [Cu(INA)₂(H₂O)₄] were studied in the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC) and Biginelli reaction under solvent-free reaction conditions. The robust, efficient and eco-friendly new method allowed the preparation of a variety of 1,2,3-triazole compounds in good to excellent yields and high selectivity for the 1,4-disubstituted triazole. Moreover, for the Biginelli reaction between aldehydes, ethyl acetoacetate and urea, the corresponding dihydropyrimidinones (DHPMs) were also obtained in satisfactory yields under mild reaction conditions for both catalysts. The comparative study between Cu(INA)₂-MOF and [Cu(INA)₂(H₂O)₄] complex demonstrated better results for the Cu-MOF, for both the yields and the regioselectivity of the products. Furthermore, no change in the heterogeneous catalyst structure was observed after the reaction, allowing them to be recovered and reused without any loss of activity.

The catalytic application of Cu(INA)₂-MOF in click and Biginelli reactions was investigated and a comparative study with the [Cu(INA)₂(H₂O)₄] complex was performed.

Novel CoNi-metal-organic framework crystal-derived CoNi@C: synthesis and effective cascade catalysis

Evaluating the catalytic influence of metal sites on derivates obtained from the calcination of metal-organic frameworks (MOFs) is very important for the rational construction of novel MOFs. Based on this catalytic functional guidance, two new Co-MOF and CoNi-MOF crystals were designed and synthesized, and further pyrolyzed to obtain corresponding porous carbon-based catalysts. Interestingly, the derivates exhibited better catalytic performance toward the tandem reaction of dehydrogenation of NH3BH3 and subsequent hydrogenation reduction of nitro/olefin compounds than those of the CoNi-ZIF (a star MOF)-derived CoNi@carbon and most metal catalysts. Significantly, the CoNi@C maintained excellent activity, even after 30 cycles, demonstrating its great longevity and durability, which are especially important for the practical application of metal catalysts in industrial catalysis.

CNTs synthesized with polyoxometalate-based metal–organic compounds as catalyst precursors via the CVD method and their adsorption performance towards organic dyes

CNTs were synthesized with POM-based compounds as catalyst precursors via the CVD method, and they possess a high adsorption capacity towards organic dyes.

MOF-derived electrocatalysts for oxygen reduction, oxygen evolution and hydrogen evolution reactions

The morphology and composition design of MOF-derived carbon-based materials and their applications for electrocatalytic ORR, OER and HER are reviewed.

Evolution of metal organic frameworks as electrocatalysts for water oxidation

The development of metal organic framework based water oxidation catalysts is discussed here in connection with various design strategies.

Magnetic core–shell Fe3O4@Cu2O and Fe3O4@Cu2O–Cu materials as catalysts for aerobic oxidation of benzylic alcohols assisted by TEMPO and N-methylimidazole

Robust core–shell magnetic materials catalyse quantitatively the aerobic oxidation of a wide range of benzylic alcohols into corresponding aldehydes at room temperature showing excellent tolerance towards the substituents on the phenyl ring.

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

We give a comprehensive overview of how the morphology control is an effective and versatile way to control the physicochemical properties of metal oxides that can be transferred to metal–organic frameworks and porous carbon materials.

Boron-Templated Dimerization of Allylic Alcohols To Form Protected 1,3-Diols via Acid Catalysis

We report an unprecedented boron-templated dimerization of allylic alcohols that generates a 1,3-diol product with two stereogenic centers in high yield and diastereoselectivity. This acid-catalyzed reaction is achieved via in situ formation of a boronic ester intermediate that facilitates selective cyclization and formation of a cyclic boronic ester product. High yields are observed with a variety of allylic alcohols, and mechanistic studies confirm the role of boron as a template for the reaction.