Tuning the activity by controlling the wettability of MOF eggshell catalysts: A quantitative structure–activity study

CO2 Capture from High-Humidity Flue Gas Using a Stable Metal–Organic Framework

The flue gas from fossil fuel power plants is a long-term stable and concentrated emission source of CO2, and it is imperative to reduce its emission. Adsorbents have played a pivotal role in reducing CO2 emissions in recent years, but the presence of water vapor in flue gas poses a challenge to the stability of adsorbents. In this study, ZIF-94, one of the ZIF adsorbents, showed good CO2 uptake (53.30 cm3/g), and the calculated CO2/N2 (15:85, v/v) selectivity was 54.12 at 298 K. Because of its excellent structural and performance stability under humid conditions, the CO2/N2 mixture was still well-separated on ZIF-94 with a separation time of 30.4 min when the relative humidity was as high as 99.2%, which was similar to the separation time of the dry gas experiments (33.2 min). These results pointed to the enormous potential applications of ZIF-94 for CO2/N2 separation under high humidity conditions in industrial settings.

Drug Delivery Using Hydrophilic Metal-Organic Frameworks (MOFs): Effect of Structure Properties of MOFs on Biological Behavior of Carriers

To study the influence of pore structural properties of metal-organic frameworks (MOFs) on drug adsorption and delivery, we synthesized two MOF termed TMU-6(RL1) {[Zn(oba)(RL1)_0.5]_n·(DMF)_1.5} and TMU-21(RL2) {[Zn(oba)(RL2)_0.5]_n·(DMF)_1.5} with amine basic N-donor pillars containing phenyl or naphthyl cores with various hydrophilic properties around the main center of the reaction. TG, IR, XPS, and PXRD analyses were used to extensively characterize the MOFs. The synthesized carriers showed high adsorption efficiency, stability, and controlled release. As an anticancer drug, Nimesulide (Nim) was adsorbed to MOFs using multiple adsorption mechanisms, such as _Hostπ-π_Guest interaction and _HostN-H···O_Guest hydrogen bonds. Moreover, Hirshfeld surface analysis showed when the benzene core was replaced with the naphthalene core, the percentage of intermolecular interactions of π···π and N···H by amine sites in TMU-21(RL2) decreased compared with TMU-6(RL1), while the percentage of these interactions with guest molecules increased. The results showed that changes in the hydrophobicity/hydrophilicity properties of MOFs would alter their ability to adsorb Nim in the pore of the frameworks. In vitro anticancer studies also showed that the cytotoxicity of Nim in MOFs@Nim composites against human cervical cancer cell line (HeLa cells) and human colon cancer cell line (HT-29 cells) is much higher than that of free Nim. Generally, based on the results, it can be said that the biological behavior of carriers can be regulated by adjusting the structure properties of MOFs.

The applications and prospects of hydrophobic metal-organic frameworks in catalysis

In recent years, large numbers of hydrophobic/superhydrophobic metal-organic frameworks (MOFs) have been developed. These hydrophobic MOFs not only retain rich structural variety, highly crystalline frameworks, and uniform micropores, but they also have lower affinity towards water and boosted hydrolytic stability. Until now, there were two main strategies to prepare hydrophobic MOFs, including a one-step method and post-synthesis modification (PSM). PSM was an often-used strategy for preparing hydrophobic MOFs. Hydrophobic MOFs showed unique advantages when used as catalysts for various categories of reactions. Herein, recent research advances relating to hydrophobic MOFs in the catalytic field are presented. The catalytic activities of hydrophobic MOFs and corresponding hydrophilic ones are also compared, and the superiority of hydrophobic MOFs or MOF materials as catalysts in 10 reactions is discussed. Finally, the advantages of hydrophobic MOFs as catalysts or auxiliary materials are summarized and promising future developments of hydrophobic MOFs are highlighted.

Zeolitic imidazolate frameworks for use in electrochemical and optical chemical sensing and biosensing: a review

This review (with 145 refs.) summarizes the progress that has been made in the use of zeolitic imidazolate frameworks in chemical sensing and biosensing. Zeolitic imidazolate frameworks (ZIFs) are a type of porous material with zeolite topological structure that combine the advantages of zeolite and traditional metal-organic frameworks. Owing to the structural flexibility of ZIFs, their pore sizes and surface functionalization can be reasonably designed. Following an introduction into the field of metal-organic frameworks and the zeolitic imidazolate framework (ZIF) subclass, a first large section covers the various kinds and properties of ZIFs. The next large section covers electrochemical sensors and assays (with subsections on methods for gases, electrochemiluminescence, electrochemical biomolecules). This is followed by main sections on ZIF-based colorimetric and luminescent sensors, with subsections on sensors for metal ions and anions, for gases, and for organic biomolecules. The last section covers SERS-based assays. Several tables are presented that give an overview on the wealth of methods and materials. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical abstract In recent years, ZIFs and their composites have been widely used as probes in chemical sensing, and these probes have shown great advantages over other materials. This review describes the current progress on ZIFs toward electrochemical, luminescence, colorimetric, and SERS-based sensing applications, highlighting the different strategies for designing ZIFs and their composites and potential challenges in this field.

Hydrophobic Metal-Organic Frameworks: Assessment, Construction, and Diverse Applications

Tens of thousands of metal-organic frameworks (MOFs) have been developed in the past two decades, and only ≈100 of them have been demonstrated as porous and hydrophobic. These hydrophobic MOFs feature not only a rich structural variety, highly crystalline frameworks, and uniform micropores, but also a low affinity toward water and superior hydrolytic stability, which make them promising adsorbents for diverse applications, including humid CO2 capture, alcohol/water separation, pollutant removal from air or water, substrate-selective catalysis, energy storage, anticorrosion, and self-cleaning. Herein, the recent research advancements in hydrophobic MOFs are presented. The existing techniques for qualitatively or quantitatively assessing the hydrophobicity of MOFs are first introduced. The reported experimental methods for the preparation of hydrophobic MOFs are then categorized. The concept that hydrophobic MOFs normally synthesized from predesigned organic ligands can also be prepared by the postsynthetic modification of the internal pore surface and/or external crystal surface of hydrophilic or less hydrophobic MOFs is highlighted. Finally, an overview of the recent studies on hydrophobic MOFs for various applications is provided and suggests the high versatility of this unique class of materials for practical use as either adsorbents or nanomaterials.

Sonochemical synthesis and structural characterization of a new nanostructured Co(II) supramolecular coordination polymer with Lewis base sites as a new catalyst for Knoevenagel condensation

A new Co(II) mixed-ligand coordination supramolecular polymer with composition [Co₂(ppda)(4-bpdh)₂(NO₃)₂]_n (1) (where, ppda=p-phenylenediacrylic acid, 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) was synthesized using solvothermal, mechanochemical and sonochemical methods. Compound 1 and the new nanostructure have been characterized by single-crystal X-ray, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM). The thermal stability of compound 1 was also studied by thermal gravimetric analysis (TGA). The surface area of these compounds was determined by BET. The single-crystal X-ray data shows a new interesting two-dimensional coordination polymer (CP). In addition, the effect of various sonication concentrations of initial reagents, power of ultrasound irradiation and also the time on the size and morphology of nano-structured coordination polymer 1 were evaluated. Moreover, it has been demonstrated that the nanostructure of the CP1 can be used as a catalyst in Knoevenagel condensation reaction.

Amine-functionalized ionic liquid-based mesoporous organosilica as a highly efficient nanocatalyst for the Knoevenagel condensation

A novel aminopropyl-containing ionic liquid-based mesoporous organosilica was prepared and characterized and its catalytic performance was studied in the Knoevenagel condensation.

A Pt/Al2O3-supported metal–organic framework film as the size-selective core–shell hydrogenation catalyst

The substituted imidazolate-based MOF (SIM-1) easily forms a homogeneous layer at the surface of millimetric platinum-loaded alumina beads. This new core–shell SIM-1@Pt/Al₂O₃ catalyst shows the fine molecular sieving effect for the Pt-catalyzed hydrogenation of carbon–carbon double bonds.

Origin of highly active metal–organic framework catalysts: defects? Defects!

This article provides a comprehensive review of the nature of catalytic sites in MOFs.

pH dependent synthesis of Zn(ii) and Cd(ii) coordination polymers with dicarboxyl-functionalized arylhydrazone of barbituric acid: photoluminescence properties and catalysts for Knoevenagel condensation

Coordination polymers of Zn(ii) and Cd(ii) act as recyclable heterogeneous catalysts for Knoevenagel condensation reaction of aldehydes with malononitrile.

Interplay between hydrophobicity and basicity toward the catalytic activity of isoreticular MOF organocatalysts

Four MOF catalysts showing different hydrophobic characters around the basic reaction center showed subtle substrate selectivity in aldol-type condensation reaction.

Metal-organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

Synthesis, structures and physical properties of mixed-ligand coordination polymers based on a V-shaped dicarboxylic ligand

Four coordination polymers based on the V-shaped H₂hfipbb ligand, (H₂hfipbb = 4,4′-(hexafluoroisopropylidene)-bis(benzoic acid), and different auxiliary linear N-donor ligands have been constructed under solvothermal conditions and structurally characterized.

Hydrophobic and moisture-stable metal–organic frameworks

A simple way to increase hydrophobicity and chemical stability in metal–organic frameworks without compromising CO₂ sorption capacity.

Applications of metal–organic frameworks in heterogeneous supramolecular catalysis

The contributions of MOFs to the field of heterogeneous supramolecular catalysis are comprehensively reviewed with regard to active sites, selectivity, as well as host–guest chemistry.

Structure–property relationships of water adsorption in metal–organic frameworks

Among porous solids, MOFs exhibit a wealth of water adsorption behaviors.

Water adsorption in MOFs: fundamentals and applications

MOF and water, friend or enemy?

Post‐synthetic Modification of MOFs

Post‐synthetic modification is increasingly recognised as an important and versatile tool in the preparation of functionalised metal organic frameworks (MOFs). The process involves one or more reactions on a pre‐formed MOF, and it can be used to prepare MOFs that are not accessible by direct combination of metal and linker. This review explores the methods and strategies that have been developed for post‐synthetically modifying MOFs, concentrating on four classes of reaction: covalent transformations of the linker, coordination of a metal centre to a linker, modification of the inorganic part of the MOF and exchange of counter‐ions. Examples of the use of the modified MOFs are given, with a focus on their utility in catalysis.

Fabrication of noble-metal catalysts with a desired surface wettability and their applications in deciphering multiphase reactions

Noble-metal Pd and Pt catalysts with a wide range of surface wettability were fabricated through an electrochemical approach and were characterized with scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and atomic force microscopy. The importance of surface wettability of solid catalysts in multiphase reactions-especially their correlation to the nature of the studied chemical system-was investigated by reducing oxygen in an alkaline solution and oxidizing hydrogen peroxide and sodium formate in alkaline or buffered solutions at the as-prepared catalysts. These experiments illustrate that the nature of a multiphase reaction plays a critical role in determining the influence of surface wettability on the catalyst performance, providing a unique approach to decipher the reaction process. The investigation allows us to gain new insights into the electrochemical oxidation of sodium formate.