Microscopic and Mesoscopic Dual Postsynthetic Modifications of Metal-Organic Frameworks

Dual-functional metal-organic framework for chemisorption and colorimetric monitoring of cyanogen chloride

Given the growing concern over the deployment of toxic chemicals in warfare, the rapid and accurate removal and detection of cyanogen chloride (CK) as a blood agent has become increasingly critical. However, conventional physisorbents and chemisorbents used in military respirators are insufficient for the effective removal of CK. In this study, we demonstrate the chemisorption and sensing abilities of Co2(m-DOBDC) (m-DOBDC4- = 4,6-dioxo-1,3-benzenedicarboxylate) for CK via electrophilic aromatic substitution (EAS) in humid environments. Unlike the chemisorption in triethylenediamine (TEDA) impregnated carbon materials, which generates by-products through hydrolysis, the electron-rich C5 sites in m-DOBDC4- ligands give rise to cyano substitution with CK. This leads to the formation of stable C-C bonds and chloride ions (Cl-) coordinating with open Co2+ sites. Such a mechanism prevents the generation of toxic by-products like cyanic acid and hydrochloric acid. Breakthrough experiments conducted in a packed-bed system conclusively demonstrated the superior CK removal capacity of Co2(m-DOBDC) (1662 min/g), compared to TEDA-impregnated activated carbon (323 min/g) under humid conditions. Considering that MOF-74 series, isostructural with Co2(m-DOBDC), barely adsorb CK under similar conditions, this finding marks a significant advancement in developing novel sorbents for CK removal. Moreover, this chemisorption not only exhibited rapid and highly efficient CK removal but also enabled colorimetric monitoring via the distinctive color change induced by the coordination of Cl- acting as σ donors. These findings facilitate the development of adsorption and sensing equipment to protect military personnel from toxic chemical threats.

Synergistic engineering of P, N-codoped carbon-confined bimetallic cobalt/nickel phosphides with tailored electronic structures for boosting urea electro-oxidation

Bimetallic phosphides exhibit superior electrocatalytic activities and synergistic effects that make them ideal electrocatalysts for the urea oxidation reaction (UOR). Herein, P, N-codoped carbon-encapsulated cobalt/nickel phosphides derived from NiCo-MOF-74 (NiCoP@PNC) and anchored on P-doped carbonized wood fiber (PCWF) for UOR were prepared through synchronous carbonization and phosphorization. By benefiting from the synergistic effect of structural and electronic modulation, NiCoP@PNC/PCWF exhibits excellent UOR electrocatalytic performance under alkaline conditions, achieving a current density of 50 mA cm-2 with a potential of only 1.34 V (vs reversible hydrogen electrode, RHE) and continuous operation for more than 72 h. In addition, for the overall urea splitting, an electrolyzer using UOR replaced OER, which required only 1.50 V to achieve a current density of 50 mA cm-2 with excellent stability, 230 mV less than that required for the HER||OER system. In-depth theoretical analysis further proves that the strong synergistic effect between Co and Ni optimizes electronic structures, yielding excellent UOR properties. The synergistic strategy of structural and electrical modulation provides broad prospects for the design and synthesis of excellent UOR electrocatalysts for energy-saving hydrogen production by using renewable resources.

A Novel Aluminum-Based Metal-Organic Framework with Uniform Micropores for Trace BTEX Adsorption

Metal-organic frameworks (MOFs) are potential porous adsorbents for benzene, toluene, ethylbenzene and xylene (BTEX). A novel MOF, using low toxic aluminum (Al) as the metal, named as ZJU-620(Al), with uniform micropore size of 8.37±0.73 Å and specific surface area of 1347 m²  g^-1 , was synthesized. It is constructed by one-dimensional rod-shaped AlO₆ clusters, formate ligands and 4,4',4''-(2,4,6-trimethylbenzene-1,3,5-triyl) tribenzoic ligands. ZJU-620(Al) exhibits excellent chemical-thermal stability and adsorption for trace BTEX, e.g., benzene adsorption of 3.80 mmol g^-1 at P/P₀ =0.01 and 298 K, which is the largest one reported. Using Grand Canonical Monte Carlo simulations and Single-crystal X-ray diffraction analyses, it was observed that the excellent adsorption could be attributed to the high affinity of BTEX molecules in ZJU-620(Al) micropores because the kinetic diameters of BTEX are close up to the pore size of ZJU-620(Al).

Mechanistic Principles for Engineering Hierarchical Porous Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have generated tremendous research interest in the past two decades, due to their high surface areas, tailorable active sites, and tunable structures. Hierarchical porous MOFs (HP-MOFs) with two or more pore systems are particularly attractive, benefiting from improved active site accessibility and enhanced mass diffusivity in applications involving bulk molecules. This review outlines the mechanistic principles used for the rational design of HP-MOFs, current techniques used to measure their hierarchical porosities, as well as their emerging applications. We then critically summarize the current challenges in this field and provide a contemporary perspective on the technological innovations that would address current synthetic challenges in the field of HP-MOFs. The aim of this review is to provide an in-depth understanding of the formation mechanisms, materials chemistry, and structural and chemical properties of HP-MOFs while exploring ways to enhance the performance of current MOF materials in a range of fields.

Composition Optimization and Microstructure Design in MOFs-Derived Magnetic Carbon-Based Microwave Absorbers: A Review

Magnetic carbon-based composites are the most attractive candidates for electromagnetic (EM) absorption because they can terminate the propagation of surplus EM waves in space by interacting with both electric and magnetic branches. Metal-organic frameworks (MOFs) have demonstrated their great potential as sacrificing precursors of magnetic metals/carbon composites, because they provide a good platform to achieve high dispersion of magnetic nanoparticles in carbon matrix. Nevertheless, the chemical composition and microstructure of these composites are always highly dependent on their precursors and cannot promise an optimal EM state favorable for EM absorption, which more or less discount the superiority of MOFs-derived strategy. It is hence of great importance to develop some accompanied methods that can regulate EM properties of MOFs-derived magnetic carbon-based composites effectively. This review comprehensively introduces recent advancements on EM absorption enhancement in MOFs-derived magnetic carbon-based composites and some available strategies therein. In addition, some challenges and prospects are also proposed to indicate the pending issues on performance breakthrough and mechanism exploration in the related field.

Large-Scale Production of Hierarchically Porous Metal-Organic Frameworks by a Reflux-Assisted Post-Synthetic Ligand Substitution Strategy

The mass production of hierarchically porous metal-organic frameworks (HP-MOFs) with adjustable morphology and size as well as retained crystallinity is highly desirable yet challenging. Herein, we have developed a versatile post-synthetic ligand substitution (PSLS) strategy to convert typical microporous MOFs and even their composites to HP-MOFs and their composites at a 10 g level and beyond in a simple reflux system. The resulting HP-MOFs feature intrinsic micropores and abundant defective mesopores, which greatly facilitate the transport and activation of large substrates for stable and efficient heterogeneous catalysis. Furthermore, the presence of defective mesopores in the HP-MOF composites improves activity and selectivity for large molecule-involved one-pot tandem catalysis. This strategy opens a new door to fast, facile, general, and scale-up production of HP-MOFs and related composites for expanding applications of conventional microporous MOF-based materials.

MOF-74-type frameworks: tunable pore environment and functionality through metal and ligand modification

This highlight demonstrates a comprehensive overview of MOF-74-type frameworks in terms of synthetic approaches and pre- or post-synthetic modification approaches.