Metal–Organic Frameworks (MOFs) and Materials Derived from MOFs as Catalysts for the Development of Green Processes

Disulfide-Driven Pore Functionalization of Metal-Organic Frameworks

Post-synthetic modification (PSM) imparts additional functionality to metal-organic frameworks (MOFs) that is often difficult to access using solvothermal synthesis. As such, expanding the repertory of PSM reactions available to the practitioner is of increased importance for the generation of materials tailored for desired applications. Herein, a method is described for the protecting group-free installation of diverse functional groups within the pores of a MIL-53(Al) analogue via disulfide bond formation. The majority of the reactions proceed with thiol-to-disulfide conversions ranging from high to nearly quantitative. The disulfide bonds are stable in various solvents and can be cleaved in the presence of a reducing agent.

Photoactive MOF-Derived Bimetallic Silver and Cobalt Nanocomposite with Enhanced Antibacterial Activity

Conventional antibiotic-based treatment of bacterial infections remains one of the most difficult challenges in medicine because of the threat of multidrug resistance caused by indiscriminate abuse. To solve these problems, it is essential to develop an effective antibacterial agent that can be used at a small dose while minimizing the occurrence of multiple resistance. Metal-organic frameworks (MOFs), which are hyper-porous hybrid materials containing metal ions linked by organic ligands, have recently attracted attention because of their strong antibacterial activity through metal-ion release, unlike conventional antibiotics. In this study, we developed a photoactive MOF-derived cobalt-silver bimetallic nanocomposite (Ag@CoMOF) by simply depositing silver nanoparticles on a cobalt-based MOF through nanoscale galvanic replacement. The nanocomposite structure continuously releases antibacterial metal ions (i.e., Ag and Co ions) in the aqueous phase and exhibits a strong photothermal conversion effect of Ag nanoparticles, accompanied by a rapid temperature increase of 25-80 °C under near-infrared (NIR) irradiation. Using this MOF-based bimetallic nanocomposite, superior antibacterial activities were achieved by 22.1-fold for Escherichia coli and 18.3-fold for Bacillus subtilis enhanced inhibition of bacterial growth in a liquid culture environment compared with the generally used chemical antibiotics. In addition, we confirmed the synergistic enhancement of the antibacterial ability of the bimetallic nanocomposite induced by NIR-triggered photothermal heating and bacterial membrane disruption even when using a small amount of the nanocomposites. We envision that this novel antibacterial agent using MOF-based nanostructures will replace traditional antibiotics to circumvent multidrug resistance and present a new approach to antibiotic development.

Comparative Study of Commercial Silica and Sol-Gel-Derived Porous Silica from Cornhusk for Low-Temperature Catalytic Methane Combustion

The synthesis and characterization of sol-gel-derived cornhusk support for low-temperature catalytic methane combustion (LTCMC) were investigated in this study. The prepared cornhusk support was impregnated with palladium and cerium oxide (Pd/CeO₂) via the classical incipient wetness method. The resulting catalyst was characterized using various techniques, including X-ray diffraction (XRD), N₂ physisorption (BET), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H₂-TPR). The catalytic performance of the Pd/CeO₂/CHSiO₂ catalyst was evaluated for methane combustion in the temperature range of 150-600 °C using a temperature-controlled catalytic flow reactor, and its performance was compared with a commercial catalyst. The results showed that the Pd/CeO₂ dispersed on SiO₂ from the cornhusk ash support (Pd/CeO₂/CHSiO₂) catalyst exhibited excellent catalytic activity for methane combustion, with a conversion of 50% at 394 °C compared with 593 °C for the commercial silica catalyst (Pd/CeO₂/commercial). Moreover, the Pd/CeO₂/CHSiO₂ catalyst displayed better catalytic stability after 10 h on stream, with a 7% marginal loss in catalytic activity compared with 11% recorded for the Pd/CeO₂/commercial catalyst. The N₂ physisorption and H₂-TPR results indicated that the cornhusk SiO₂ support possessed a higher surface area and strong reducibility than the synthesized commercial catalyst, contributing to the enhanced catalytic activity of the Pd/CeO₂/SiO₂ catalyst. Overall, the SiO₂ generated from cornhusk ash exhibited promising potential as a low-cost and environmentally friendly support for LTCMC catalysts.

CuI nanoparticle-immobilized on a hybrid material composed of IRMOF-3 and a sulfonamide-based porous organic polymer as an efficient nanocatalyst for one-pot synthesis of 2,4-diaryl-quinolines

As a significant class of synthetic and natural products with multiple biological activities, quinolines are used in medical and electronic devices. In this study, a novel method is presented to synthesize 2,4-diarylquinoline derivatives via a simple one-pot multicomponent reaction between phenylacetylenes, aniline derivatives, and aldehydes in CH₃CN using IRMOF-3/PSTA/Cu. Notably, polymer/MOF is stabilized through a reaction between a sulfonamide-triazine-based porous organic polymer [poly (sulfonamide-triazine)](PSTA) and an amino-functionalized zinc metal-organic framework (IRMOF-3). Next, the prepared nanocomposites (IRMOF-3/PSTA) are modified using copper iodide nanoparticles (CuI NPs). Overall, the high product yields, facile recovery of nanocatalysts, short reaction times, and broad substrate range make this process environmentally friendly, practical, and economically justified.

Rationally Designed Manganese-Based Metal-Organic Frameworks as Altruistic Metal Oxide Precursors for Noble Metal-Free Oxygen Reduction Reaction

The sluggish oxygen reduction reaction (ORR) at the cathode is challenging and hinders the growth of hydrogen fuel cells. Concerning kinetic values, platinum is the best known catalyst for ORR; however, its less abundance, high cost, and corrosive nature warrant the development of low-cost catalysts. We report the hydrothermal synthesis of two novel Mn-based metal-organic frameworks (MOFs), [Mn₂(DOT)(H₂O)₂]_n (Mn-SKU-1) and [Mn₂(DOT)₂(BPY)₂(THF)]_n (Mn-SKU-2) (DOT = 2,5-dihydroxyterephthalate; BPY = 4,4'-bipyridine). Mn-SKU-1 contains dimeric Mn(II) centers where the two corner-shared MnO₆ octahedra fuse to give rise to an infinite Mn₂O₁₀ cluster, whereas the two Mn(II) ions coordinate to DOT and BPY moieties to give rise to a pillared structure in Mn-SKU-2 and form a 3D → 3D homo-interpenetration MOF with a twofold interpenetrated net. The pyrolysis of as-synthesized Mn-MOFs at 600 °C under N₂ produced exclusively porous α-Mn₂O₃ composites (PSKU-1 and PSKU-2), with the BET surface area of 90.8 (for PSKU-1) and 179.3 m² g^-1 (for PSKU-2). These mesoporous MOF-derived α-Mn₂O₃ composites were modified as cathode materials for the electrocatalytic reduction of oxygen. The onset potential for the oxygen reduction reaction was found to be 0.90 V for PSKU-1 and 0.93 V for PSKU-2 versus RHE in 0.1 M KOH solution, with the current density of 4.8 and 6.0 mA cm^-2, respectively, at 1600 rpm. Based on the RDE/RRDE results, the electrocatalytic oxygen reduction occurs majorly via the four-electron process. The electrocatalyst PSKU-2 is cheap, easy to use, retains 90% of its activity after 10 h of continuous use, and offers higher recyclability than Pt/C. The onset potential maximum current density and kinetic values (J_k = 11.68 mA cm^-2 and Tafel slope = 85.0 mV dec^-1) obtained in this work are higher than the values reported for pure Mn₂O₃.

The Progress of Metal-Organic Framework for Boosting CO2 Conversion

With the rapid development of modern society, environmental problems, including excessive amounts of CO2 released in the atmosphere, are becoming more and more serious. It is necessary to develop new materials and technologies to reduce pollution. Among them, metal–organic frameworks (MOFs) have shown potential for application in the area of catalysis due to their ultra-high specific surface area, structural versatility, and designability as well as ease of modification and post-synthesis. Herein, we summarize recent research advances by use of MOFs for boosting CO2 conversion. Furthermore, challenges and possible research directions related to further exploration are also discussed.