Effect of Spatial Heterogeneity on the Unusual Uptake Behavior of Multivariate-Metal-Organic Frameworks

Multivariate Flexible Metal-Organic Frameworks and Covalent Organic Frameworks

Precise control of the void environment, achieved through multiple functional groups and enhanced by structural adaptations to guest molecules, stands at the forefront of scientific inquiry. Flexible multivariate open framework materials (OFMs), including covalent organic frameworks and metal-organic frameworks, meet these criteria and are expected to play a crucial role in gas storage and separation, pollutant removal, and catalysis. Nevertheless, there is a notable lack of critical evaluation of achievements in their chemistry and future prospects for their development or implementation. To provide a comprehensive historical context, the initial discussion explores into the realm of "classical" flexible OFMs, where their origin, various modes of flexibility, similarities to proteins, advanced tuning methods, and recent applications are explored. Subsequently, multivariate flexible materials, the methodologies involved in their synthesis, and horizons of their application are focussed. Furthermore, the reader to the concept of spatial distribution is introduced, providing a brief overview of the latest reports that have contributed to its elucidation. In summary, the critical review not only explores the landscape of multivariate flexible materials but also sheds light on the obstacles that the scientific community must overcome to fully unlock the potential of this fascinating field.

Reticular Materials for Photocatalysis

Photocatalysis leverages solar energy to overcome the thermodynamic barrier, enabling efficient chemical reactions under mild conditions. It can greatly reduce reliance on traditional energy sources and has attracted significant research interest. Reticular materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), represent a class of crystalline materials constructed from molecular building blocks linked by coordination and covalent bonds, respectively. Reticular materials function as heterogeneous catalysts, combining well-defined structures and high tailorability akin to homogeneous catalysts. In this review, the regulation of light absorption, charge separation, and surface reactions in the photocatalytic process through precise molecular-level design based on the features of reticular materials is elaborated. Notably, for MOFsmicroenvironment modulation around catalytic sites affects photocatalytic performance is delved, with emphasis on their unique dynamic and flexible microenvironments. For COFs, the inherent excitonic effects due to their fully organic nature is discussed and highlight the strategies to regulate excitonic effects for charge- and/or energy-transfer-mediated photocatalysis. Finally, the current challenges and future directions in this field, aiming to provide a comprehensive understanding of how reticular materials can be optimized for enhanced photocatalysis is discussed.

Positional Isomerism: A Novel Paradigm for Enhancing Iodine Adsorption in Functionalized Metal-Organic Frameworks

Porous metal-organic frameworks (MOFs) have shown great potential as adsorbents for capturing radioiodine, a major fission product generated during the reprocessing of nuclear fuel. However, studies exploring the correlation between the structure of MOFs and iodine uptake capacity remain notably rare. In this study, we introduce a new strategy for enhancing the iodine adsorption efficiency of MOFs by strategically varying the position of functional groups on the organic linkers. Employing ligand-functionalized UiO-67 MOFs, our findings reveal that ortho-amino substitution of UiO-67-o-NH2, proximal to the node of the dicarboxylate linker, markedly accelerates adsorption kinetics of iodine vapor in comparison to meta-amino substitution of UiO-67-m-NH2, where the amino groups are oriented away from the node. In contrast, UiO-67-m-NH2 exhibits a higher adsorption capacity of 2.19 g/g, compared to 1.91 g/g for UiO-67-o-NH2, attributable to its higher porosity. Furthermore, a competitive I2/H2O vapor adsorption study demonstrated that UiO-67-o-NH2 exhibits faster adsorption kinetics and higher selectivity for iodine in the presence of water vapor compared to UiO-67-m-NH2. Additionally, the crucial influence of positional isomerism on enhancing iodine adsorption has been corroborated through Raman spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. These analyses reveal that the nitrogen atom positioned at the ortho site demonstrates a stronger affinity for iodine molecules compared to the nitrogen atom at the meta site, thereby improving adsorption kinetics.

Steering diffusion selectivity of chemical isomers within aligned nanochannels of metal-organic framework thin film

The movement of molecules (i.e. diffusion) within angstrom-scale pores of porous materials such as metal-organic frameworks (MOFs) and zeolites is influenced by multiple complex factors that can be challenging to assess and manipulate. Nevertheless, understanding and controlling this diffusion phenomenon is crucial for advancing energy-economic membrane-based chemical separation technologies, as well as for heterogeneous catalysis and sensing applications. Through precise assessment of the factors influencing diffusion within a porous metal-organic framework (MOF) thin film, we have developed a chemical strategy to manipulate and reverse chemical isomer diffusion selectivity. In the process of cognizing the molecular diffusion within oriented, angstrom-scale channels of MOF thin film, we have unveiled a dynamic chemical interaction between the adsorbate (chemical isomers) and the MOF using a combination of kinetic mass uptake experiments and molecular simulation. Leveraging the dynamic chemical interactions, we have reversed the haloalkane (positional) isomer diffusion selectivity, forging a chemical pathway to elevate the overall efficacy of membrane-based chemical separation and selective catalytic reactions.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

Application and prospects of metal–organic frameworks in photocatalytic self-cleaning membranes for wastewater treatment

By loading photocatalytic MOF onto the separation membrane, the self-cleaning function of the membrane can be realized. This paper discusses the structure, synthesis, and properties of photocatalytic MOFs.

A metal organic framework-derived octahedral Cu1.95S@CoS2 for secondary batteries displaying long cycle life and stable temperature tolerance

Low-cost and safe batteries are considered to be promising energy-storage systems. Here, a metal organic framework (MOF)-derived octahedral Cu1.95S@CoS2 composite is developed as a high-performance cathode of aluminium-ion (Al-ion) batteries. CoS2 nanoparticles on Cu1.95S provide active sites, making AlCl4- intercalation/deintercalation highly reversible, and reducing polarization. Cycling at 0.5 A g-1, Cu1.95S@CoS2 maintains stable capacities of 136.6 and 122.4 mA h g-1 after 200 cycles at room temperature and -10 °C, respectively. Stable rate-performance is also achieved. These findings will accelerate the application of Al-ion batteries and MOF-derived energy-storage composites.

A nanowire-on-microrod polyaniline@FeS2 hybrid as the cathode in high-performance Al-ion batteries

A nanowire-on-microrod structured polyaniline (PANI)@FeS2 hybrid was developed via a facile metal-organic framework (MOF)-derived chemical method. The in situ grown PANI nanowires on the surface of pyramidal FeS2 microrods displayed better mechanical flexibility and improved Al-storage performance. The PANI nanowires not only enhanced electron transfer during the electrochemical reaction, but also accommodated the volume expansion of FeS2 during discharge. The PANI@FeS2 hybrid as the cathode in AIBs delivered a reliable battery capacity of 152.8 mA h g-1 along with a Coulombic efficiency of >96.5% after 500 cycles at a current density of 1.5 A g-1. In addition, a high capacity retention of 160.2 mA h g-1 after 150 cycles at 0.5 A g-1 at -10 °C was achieved. These findings provide a feasible strategy by constructing a nanowire-on-microrod hybrid that can be applied in high-performance secondary batteries.

Enzyme‐Encapsulated Protein Trap Engineered Metal–Organic Framework‐Derived Biomineral Probes for Non‐Invasive Prostate Cancer Surveillance

A paper‐based naked‐eye recognition assay with enzyme‐encapsulated protein engineered metal–organic framework‐derived biominerals is developed for direct quantification of sarcosine in urine samples for screening of prostate cancer individuals. The detection strategy stems from the successful construction of a cascade response model, which involves the introduction of a cascade enzymatic catalytic reaction on Pt nanoparticles (NPs)‐loaded porous CeO2 by integrating a sarcosine oxidase as a special recognition unit and a chromogenic substrate as a signal molecule reporter. Pt NPs‐loaded CeO2 is subjected to a one‐step thermal treatment based on multilayered mesoporous Ce‐based metal–organic framework, and the calcined CeO2 exhibits the same distinct porous graded structure. Importantly, introduction of Pt NPs sharply enhances the peroxidase‐like activity of CeO2, which is considered to be caused by the difference in the adsorption behavior of hydrogen peroxide on the CeO2 surface and Pt/CeO2 obtained by density functional theory calculations. On the basis of this, the probe is used on a mass‐producible paper‐based working platform and 3D‐printed device to specifically screen for minor differences in sarcosine between urine samples from cancer patients and normal individuals. Enzyme‐assisted cascade catalytic reaction can be extended by replacing different recognition units for multiple analytes.