Creating hierarchical pores in metal-organic frameworks via postsynthetic reactions.

Metal-organic frameworks (MOFs) demonstrate promise for a multitude of applications owing to their high porosity and surface area. However, the majority of conventional MOFs possess only micropores with very limited accessibility to substances larger than 2 nm-especially functional biomacromolecules like some proteins. It is challenging to create an appropriately large pore size while avoiding framework collapse in MOFs. Herein, we present the generation of mesopores in microporous MOFs through three facile and effective techniques, namely Soxhlet washing, linker hydrolysis and linker thermolysis. These postsynthetic elimination approaches have been applied in selected MOFs, including PCN-250, PCN-160 and UiO-66, and controllably generate MOFs with hierarchical pores and high stability. Our work demonstrates reproducible and straightforward methods resulting in hierarchically porous materials that possess the benefits of mesoporosity while borrowing the robustness of a micropore framework. All the procedures can be conducted reliably at a multigram scale and operation time less than 6 h, representing a significant effort in the field of MOF synthesis. These hierarchically porous MOFs show great promise in a wide range of applications as efficient adsorbents, catalysts and drug carriers.

Rapid Generation of Hierarchically Porous Metal-Organic Frameworks through Laser Photolysis.

Hierarchically porous metal-organic frameworks (HP-MOFs) facilitate mass transfer due to mesoporosity while preserving the advantage of microporosity. This unique feature endows HP-MOFs with remarkable application potential in multiple fields. Recently, new methods such as linker labilization for the construction of HP-MOFs have emerged. To further enrich the synthetic toolkit of MOFs, we report a controlled photolytic removal of linkers to create mesopores within microporous MOFs at tens of milliseconds. Ultraviolet (UV) laser has been applied to eliminate "photolabile" linkers without affecting the overall crystallinity and integrity of the original framework. Presumably, the creation of mesopores can be attributed to the missing-cluster defects, which can be tuned through varying the time of laser exposure and ratio of photolabile/robust linkers. Upon laser exposure, MOF crystals shrank while metal oxide nanoparticles formed giving rise to the HP-MOFs. In addition, photolysis can also be utilized for the fabrication of complicated patterns with high precision, paving the way towards MOF lithography, which has enormous potential in sensing and catalysis.

Effect of Isomorphic Metal Substitution on the Fenton and Photo-Fenton Degradation of Methylene Blue Using Fe-Based Metal-Organic Frameworks.

The removal of toxic organic compounds (TOCs) using highly porous solids such as metal-organic frameworks (MOFs) has gained significant attention over the past decade. In this study, it has been demonstrated that the efficiency of PCN-250 as a heterogeneous catalyst porous coordination network (PCN) for both Fenton and photo-Fenton reactions can be improved by the isomorphic substitution of Mn and Co for Fe, while it can be inhibited by the substitution of Ni for Fe. Furthermore, the Mn-substituted sample named PCN-250(Fe2Mn) decomposed 100% of methylene blue (MB) in solution in 300 min and displayed good recyclability over three cycles. This work establishes that the highly porous, commercially available, and robust family of MOFs named PCN-250 has the potential to be used as catalysts for Fenton and photo-Fenton reactions as well as broader advanced oxidation processes (AOP) for water purification applications. Overall, this work successfully demonstrates not only the ability to perform isomorphic substitution of various metals within MOFs but also the effect of the substitution on the resulting catalytic performance.

Metal oxide decorated porous carbons from controlled calcination of a metal-organic framework.

Thermal decomposition of an iron-based MOF was conducted under controlled gas environments to understand the resulting porous carbon structure. Different phases and crystallite sizes of iron oxide are produced based on the specific gas species. In particular, air resulted in iron(iii) oxide, and D2O and CO2 resulted in the mixed valent iron(ii,iii) oxide. Performing the carbonization under non-oxidative or reducing conditions (N2, He, H2) resulted in the formation of a mixture of both iron(ii,iii) oxide and iron(iii) oxide. Based on in situ and air-free handling experiments, it was observed that this is partially due to the formation of zero-valent iron metal that is rapidly oxidized when exposed to air. Neutron pair distribution function analysis provided insight into the effect of the gas environment on the local structure of the porous carbon, indicating a noticeable change in local order between the D2O and the N2 calcined samples.

The thermally induced decarboxylation mechanism of a mixed-oxidation state carboxylate-based iron metal-organic framework.

Investigations into a thermally generated decarboxylation mechanism for metal site activation and the generation of mesopores in a carboxylate iron-based MOF, PCN-250, have been conducted. PCN-250 exhibits an interesting oxidation state change during thermal treatment under inert atmospheres or vacuum conditions, transitioning from an Fe(iii)3 cluster to a Fe(ii)Fe(iii)2 cluster. To probe this redox event and discern a mechanism of activation, a combination of thermogravimetric analysis, gas sorption, scanning electron microscopy, 57Fe Mössbauer spectroscopy, gas chromatography-mass spectrometry, and X-ray diffraction studies were conducted. The results suggest that the iron-site activation occurs due to ligand decarboxylation above 200 °C. This is also consistent with the generation of a missing cluster mesoporous defect in the framework. The resulting mesoporous PCN-250 maintains high thermal stability, preserving crystallinity after multiple consecutive high-temperature regeneration cycles. Additionally, the thermally reduced PCN-250 shows improvements in the total uptake capacity of methane and CO2.

Metal-Organic Frameworks for Food Safety.

Food safety is a prevalent concern around the world. As such, detection, removal, and control of risks and hazardous substances present from harvest to consumption will always be necessary. Metal-organic frameworks (MOFs), a class of functional materials, possess unique physical and chemical properties, demonstrating promise in food safety applications. In this review, the synthesis and porosity of MOFs are first introduced by some representative examples that pertain to the field of food safety. Following that, the application of MOFs and MOF-based materials in food safety monitoring, food processing, covering preservation, sanitation, and packaging is overviewed. Future perspectives, as well as potential opportunities and challenges faced by MOFs in this field will also be discussed. This review aims to promote the development and progress of MOF chemistry and application research in the field of food safety, potentially leading to novel solutions.

From fundamentals to applications: a toolbox for robust and multifunctional MOF materials.

In recent years, metal-organic frameworks (MOFs) have been regarded as one of the most important classes of materials. The combination of various metal clusters and ligands, arranged in a vast array of geometries has led to an ever-expanding MOF family. Each year, new and novel MOF structures are discovered. The structural diversity present in MOFs has significantly expanded the application of these new materials. MOFs show great potential for a variety of applications, including but not limited to: gas storage and separation, catalysis, biomedicine delivery, and chemical sensing. This review intends to offer a short summary of some of the most important topics and recent development in MOFs. The scope of this review shall cover the fundamental aspects concerning the design and synthesis of MOFs and range to the practical applications regarding their stability and derivative structures. Emerging trends of MOF development will also be discussed. These trends shall include multicomponent MOFs, defect development in MOFs, and MOF composites. The ever important structure-property-application relationship for MOFs will also be investigated. Overall, this review provides insight into both existing structures and emerging aspects of MOFs.

Incorporating Heavy Alkanes in Metal-Organic Frameworks for Optimizing Adsorbed Natural Gas Capacity.

Metal-organic frameworks (MOFs) as methane adsorbents are highly promising materials for applications such as methane-powered vehicles, flare gas capture, and field natural gas separation. Pre- and post-synthetic modification of MOFs have been known to help improve both the overall methane uptake as well as the working capacity. Here, a post-synthetic modification strategy to non-covalently modify MOF adsorbents for the enhancement of the natural gas uptake for the MOF material is introduced. In this study, PCN-250 adsorbents were doped with C10 alkane and C14 fatty acid and their impact on the methane uptake capabilities was investigated. It was found that even trace amounts of heavy hydrocarbons could considerably enhance the raw methane uptake of the MOF while still being regenerable. The doped hydrocarbons are presumably located at the mesoporous defects of PCN-250, thus optimizing the framework-methane interactions. These findings reveal a general approach that can be used to modify the MOF absorbents, improving their ability to be sustainable and renewable natural gas adsorption platforms.