Tailoring Zirconium-based metal organic frameworks for enhancing Hydrophilic/Hydrophobic Characteristics: Simulation and experimental investigation

Defect Engineering in Ce-Based Metal-Organic Frameworks toward Enhanced Catalytic Performance for Hydrogenation of Dicyclopentadiene

Defective metal-organic frameworks (MOFs) have shown great potential for catalysis due to abundant active sites and adjustable physical and chemical properties. A series of Ce-based MOFs with different defect contents were synthesized via a modulator-induced defect engineering strategy with the aid of the cell pulverization technique. The effects of modulators on the pore structure, morphology, valence distribution of Ce, and Lewis acidity of Ce-MOF-801 were systematically investigated. Among the different samples studied, the optimal Ce-MOF-801-50eq sample exhibited remarkable catalytic activity for DCPD hydrogenation, achieving a conversion rate of 100%, which is significantly higher compared to other Ce-MOF-801-neq samples as well as the Zr-MOF-801-50eq and Hf-MOF-801-50eq samples. The enhanced catalytic performance of Ce-MOF-801-50eq can be attributed to advantages provided by defect engineering, such as the high specific surface area, proper pore size distribution, abundant unsaturated metal sites, and Ce3+/Ce4+ atom ratio, which have been supported by various characterizations. This study provides important insights into the rational design of Ce-MOFs in the field of catalytic DCPD hydrogenation.

Engineered Nanoporous Frameworks for Adsorption Cooling Applications

The energy demand for traditional vapor-compressed technology for space cooling continues to soar year after year due to global warming and the increasing human population's need to improve living and working conditions. Thus, there is a growing demand for eco-friendly technologies that use sustainable or waste energy resources. This review discusses the properties of various refrigerants used for adsorption cooling applications followed by a brief discussion on the thermodynamic cycle. Next, sorbents traditionally used for cooling are reviewed to emphasize the need for advanced capture materials with superior properties to improve refrigerant sorption. The remainder of the review focus on studies using engineered nanoporous frameworks (ENFs) with various refrigerants for adsorption cooling applications. The effects of the various factors that play a role in ENF-refrigerant pair selection, including pore structure/dimension/shape, morphology, open-metal sites, pore chemistry and possible presence of defects, are reviewed. Next, in-depth insights into the sorbent-refrigerant interaction, and pore filling mechanism gained through a combination of characterization techniques and computational modeling are discussed. Finally, we outline the challenges and opportunities related to using ENFs for adsorption cooling applications and provide our views on the future of this technology.

When Polymorphism in Metal-Organic Frameworks Enables Water Sorption Profile Tunability for Enhancing Heat Allocation and Water Harvesting Performance

The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- µ-OH-connected corner-sharing AlO4(OH)2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers, and cis-µ-OH-connected corner-sharing AlO4(OH)2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc has a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P0 ≈ 0.5 in MIL-53-muc, to P/P0 ≈ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo reveal that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations show that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60 °C, outperforming benchmark sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air.

Recent Advances in Metal-Organic Framework-Based Nanomaterials for Electrocatalytic Nitrogen Reduction

The production of ammonia under moderate conditions is of environmental and sustainable importance. The electrochemical nitrogen reduction reaction (E-NRR) method has been intensively investigated in the recent decades. Nowadays, the further development of E-NRR is largely hindered by the lack of competent electrocatalysts. Metal-organic frameworks (MOFs) are considered as the next-generation catalysts for E-NRR, featuring their tailorable structures, abundant active sites and favorable porosity. To present a comprehensive review on both the fundamental and advanced development in MOFs catalyst-based E-NRR field, this paper first introduces the basic principles of E-NRR, including the reaction mechanism, major apparatus components, performance criteria, and ammonia detection protocols. Next, the synthesis and characterization methods for MOFs and their derivatives are discussed. In addition, a reaction mechanism study via density functional theory calculations is also presented. After that, the recent advancement of MOF-based catalysts in the E-NRR field as well as the modification approaches on MOFs for E-NRR optimization is elaborated. Finally, the current challenges and outlook of MOF catalyst-based E-NRR field are emphasized.

Water Adsorption Dynamics on Metal-Organic Framework MOF-801: Comparative Study of Loose and Glued Grains, and Coatings

Adsorption heat transformation and storage (AHTS) is an environmentally benign and energy-saving alternative to common compression chillers and heat pumps. The low specific power (SP) of adsorption systems is a key drawback that hinders their broader dissemination. The optimization of adsorption dynamics is a prerequisite for SP enhancement. In this work, we studied the dynamics of water vapor adsorption on MOF-801-a promising adsorbent for AHTS. For the first time, two configurations of compact MOF-801 bed, namely, grains glued to the surface of a metal support and thin adsorbent coatings, are prepared, and their porous structure is characterized. The water adsorption dynamics is compared with a common loose grains configuration. The main findings are: (a) the binder can both accelerate and decelerate the water adsorption, and its chemical nature is subject to careful selection; (b) at the initial time, heat transfer between the support and adsorbent bed controls the adsorption rate, and, at a longer time, mass transfer starts to affect it; (c) polyvinylpyrrolidone, bentonite, thermal grease, and hydroxyethylcellulose increase the heat transfer coefficients and accelerate adsorption; polyvinyl alcohol and polyaniline slow it down; and (d) for the coatings prepared with polyvinylpyrrolidone, an SP of 1.6-5.1 kW/kg can be achieved, which is about twice that for the loose grains. The new configurations can be recommended for effective but expensive adsorbents such as MOFs, and their implementation will contribute to the further spread of AHTS technology.