Search Results (14)

In this study, cerium-based metal–organic frameworks (MOFs), cerium terephthalate (CeTPA), were synthesized and incorporated into nanofibers via electrospinning using poly(methyl methacrylate) (PMMA). The synthesized materials were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Tauc plot analysis. The electrospun CeTPA nanofibers exhibited superhydrophobic properties, with water contact angles exceeding 150°. The adsorption and catalytic performance of the nanofibers were assessed for dye removal using Congo red (CR) and methylene blue (MB) as model organic pollutants. Adsorption studies demonstrated negligible dye uptake due to the hydrophobicity of the fibers, while catalytic degradation experiments in the presence of hydrogen peroxide (H₂O₂) showed significant degradation of CR but limited effectiveness against MB, offering high selectivity toward anionic dyes. Structural and optical characterizations confirmed the stability and catalytic activity of CeTPA nanofibers, highlighting their potential for selective dye degradation in wastewater treatment applications. Full article

For hydrogen-powered vehicles, the efficiency cost brought about by the current industry choices of hydrogen storage methods greatly reduces the system’s overall efficiency. The physisorption of hydrogen fuel onto metal–organic frameworks (MOFs) is a promising alternative storage method due to their large surface areas and exceptional tunability. However, the massive selection of MOFs poses a challenge for the efficient screening of top-performing MOF structures that are capable of meeting target hydrogen uptakes. This study examined the performance of 13 machine learning (ML) models in the prediction of the gravimetric and volumetric hydrogen uptakes of real MOF structures for comparison with simulated and experimental results. Among the 13 models studied, 12 models gave an R² greater than 0.95 in the prediction of both the gravimetric and the volumetric uptakes in MOFs. In addition, this study introduces a 4-20-1 ANN model that predicts the bulk, shear, and Young’s moduli for the MOFs. The machine learning models with high R² can be used in choosing MOFs for hydrogen storage. Full article

A 3D hydrogen-bonded metal-organic framework, [Cu(apc)₂]_n (TJU-Dan-5, Hapc = 2-aminopyrimidine-5-carboxylic acid), was synthesized via a solvothermal reaction. The activated TJU-Dan-5 with permanent porosity exhibits a moderate uptake of 1.52 wt% of hydrogen gas at 77 K. The appropriate BET surface areas and decoration of the internal polar pore surfaces with groups that form extensive hydrogen bonds offer a more favorable environment for selective C₂H₆ adsorption, with a predicted selectivity for C₂H₆/CH₄ of around 101 in C₂H₆/CH₄ (5:95, v/v) mixtures at 273 K under 100 kPa. The molecular model calculation demonstrates a C–H···π interaction and a van der Waals host–guest interaction of C₂H₆ with the pore walls. This work provides a strategy for the construction of 3D hydrogen-bonded MOFs, which may have great potential in the purification of natural gas. Full article

In the present work, ab initio calculations and Monte Carlo simulations were combined to investigate the effect of linker functionalization on nitric oxide (NO)’s storage ability of metal–organic frameworks (MOFs). The binding energy (BE) of nitric oxide with a set of forty-two strategically selected, functionalized benzenes was investigated using Density Functional Theory calculations at the RI-DSD-BLYP/def2-TZVPP level of theory. It was found that most of the functional groups (FGs) increased the interaction strength compared to benzene. Phenyl hydrogen sulfate (–OSO₃H) was the most promising among the set of ligands, with an enhancement of 150%. The organic linker of IRMOF-8 was modified with the three top-performing functional groups (–OSO₃H, –OPO₃H₂, –SO₃H). Their ability for NO adsorption was investigated using Grand Canonical Monte Carlo (GCMC) simulations at an ambient temperature and a wide pressure range. The results showed great enhancement in NO uptake constituting the above-mentioned FGs, suggesting them to be promising modification candidates in a plethora of porous materials. Full article

Green methanol is a viable alternative for the storage of hydrogen and may be produced from captured anthropogenic sources of carbon dioxide. The latter was hydrogenated over Cu-ZnO catalysts supported on an aluminum fumarate metal-organic framework (AlFum MOF). The catalysts, prepared via slurry phase impregnation, were assessed for thermocatalytic hydrogenation of CO₂ to methanol. PXRD, FTIR, and S_BET exhibited a decrease in crystallinity of the AlFum MOF support after impregnation with Cu-Zn active sites. SEM, SEM-EDS, and TEM revealed that the morphology of the support is preserved after metal loading, where H₂-TPR confirmed the presence of active sites for hydrogen uptake. The catalysts exhibited good activity, with a doubling in Cu and Zn loading over the AlFum MOF, resulting in a 4-fold increase in CO₂ conversions from 10.8% to 45.6% and an increase in methanol productivity from 34.4 to 56.5 g_MeOH/Kg_cat/h. The catalysts exhibited comparatively high CO selectivity and high yields of H₂O, thereby favoring the reverse water-gas shift reaction. The selectivity of the catalysts towards methanol was found to be 12.9% and 6.9%. The performance of the catalyst supported on AlFum MOF further highlights the potential use of MOFs as supports in the heterogeneous thermocatalytic conversion of CO₂ to value-added products. Full article

Carbon dioxide (CO₂) is generally unavoidable during the production of fuel gases such as hydrogen (H₂) from steam reformation and syngas composed of carbon monoxide (CO) and hydrogen (H₂). Efficient separation of CO₂ from these gases is highly important to improve the energetic utilization efficiency and prevent poisoning during specific applications. Metal–organic frameworks (MOFs), featuring ordered porous frameworks, high surface areas and tunable pore structures, are emerging porous materials utilized as solid adsorbents for efficient CO₂ capture and separation. Furthermore, the construction of hierarchical MOFs with micropores and mesopores could further promote the dynamic separation processes, accelerating the diffusion of gas flow and exposing more adsorptive pore surface. Herein, we report a simple, efficient, one-pot template-mediated strategy to fabricate a hierarchically porous CuBTC (CuBTC-Water, BTC = 1,3,5-benzenetricarboxylate) for CO₂ separation, which demonstrates abundant mesopores and the superb dynamic separation ability of CO₂/N₂. Therefore, CuBTC-Water demonstrated a CO₂ uptake of 180.529 cm³ g⁻¹ at 273 K and 1 bar, and 94.147 cm³ g⁻¹ at 298 K and 1 bar, with selectivity for CO₂/N₂ mixtures as high as 56.547 at 273 K, much higher than microporous CuBTC. This work opens up a novel avenue to facilely fabricate hierarchically porous MOFs through one-pot synthesis for efficient dynamic CO₂ separation. Full article

The interaction strength of nitrogen dioxide (NO₂) with a set of 43 functionalized benzene molecules was investigated by performing density functional theory (DFT) calculations. The functional groups under study were strategically selected as potential modifications of the organic linker of existing metal–organic frameworks (MOFs) in order to enhance their uptake of NO₂ molecules. Among the functional groups considered, the highest interaction energy with NO₂ (5.4 kcal/mol) was found for phenyl hydrogen sulfate (-OSO₃H) at the RI-DSD-BLYP/def2-TZVPP level of theory—an interaction almost three times larger than the corresponding binding energy for non-functionalized benzene (2.0 kcal/mol). The groups with the strongest NO₂ interactions (-OSO₃H, -PO₃H₂, -OPO₃H₂) were selected for functionalizing the linker of IRMOF-8 and investigating the trend in their NO₂ uptake capacities with grand canonical Monte Carlo (GCMC) simulations at ambient temperature for a wide pressure range. The predicted isotherms show a profound enhancement of the NO₂ uptake with the introduction of the strongly-binding functional groups in the framework, rendering them promising modification candidates for improving the NO₂ uptake performance not only in MOFs but also in various other porous materials. Full article

Water adsorption in metal–organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be −12.7 Kcal/mol for the -OSO₃H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm³/cm³ for all candidates, classifying them among the top performing materials for water harvesting. Full article

Storage is still limiting the implementation of hydrogen as an energy carrier to integrate the intermittent operation of renewable energy sources. Among different solutions to the currently used compressed or liquified hydrogen systems, physical adsorption at cryogenic temperature in porous materials is an attractive alternative due to its fast and reversible operation and the resulting reduction in storage pressure. The feasibility of cryoadsorption for hydrogen storage depends mainly on the performance of the used materials for the specific application, where metal-organic frameworks or MOFs are remarkable candidates. In this work, gravimetric and volumetric hydrogen uptakes at 77 K and up to 100 bar of commercially available MOFs were measured since these materials are made from relatively cheap and accessible building blocks. These materials also show relatively high porous properties and are currently near to large-scale production. The measuring device was calibrated at different room temperatures to calculate an average correction factor and standard deviation so that the correction deviation is included in the measurement error for better comparability with different measurements. The influence of measurement conditions was also studied, concluding that the available adsorbing area of material and the occupied volume of the sample are the most critical factors for a reproducible measurement, apart from the samples’ preparation before measurement. Finally, the actual volumetric storage density of the used powders was calculated by directly measuring their volume in the analysis cell, comparing that value with the maximum volumetric uptake considering the measured density of crystals. From this selection of commercial MOFs, the materials HKUST-1, PCN-250(Fe), MOF-177, and MOF-5 show true potential to fulfill a volumetric requirement of 40 g·L⁻¹ on a material basis for hydrogen storage systems without further packing of the powders. Full article

In metal-organic frameworks (MOFs), mixed-metal clusters have the opportunity to adsorb hydrogen molecules due to a greater charge density of the metal. Such interactions may subsequently enhance the gravimetric uptake of hydrogen. However, only a few papers have explored the ability of mixed-metal MOFs to increase hydrogen uptake. The present work reveals the preparation of mixed metal metal-organic frameworks M-MOF-5 (where M = Ni²⁺, Co²⁺, and Fe²⁺) (where MOF-5 designates MOFs such as Zn²⁺ and 1,4-benzenedicarboxylic acid ligand) using the post-synthetic exchange (PSE) technique. Powder X-ray diffraction patterns and scanning electron microscopy images indicate the presence of crystalline phases after metal exchange, and the inductively coupled plasma–mass spectroscopy analysis confirmed the exchange of metals by means of the PSE technique. The nitrogen adsorption isotherms established the production of microporous M-MOF-5. Although the additional metal ions decreased the surface area, the exchanged materials displayed unique features in the gravimetric uptake of hydrogen. The parent MOF-5 and the metal exchanged materials (Ni-MOF-5, Co-MOF-5, and Fe-MOF-5) demonstrated hydrogen capacities of 1.46, 1.53, 1.53, and 0.99 wt.%, respectively. The metal-exchanged Ni-MOF-5 and Co-MOF-5 revealed slightly higher H₂ uptake in comparison with MOF-5; however, the Fe-MOF-5 showed a decrease in uptake due to partial discrete complex formation (discrete complexes with one or more metal ions) with less crystalline nature. The Sips model was found to be excellent in describing the H₂ adsorption isotherms with a correlation coefficient ≅ 1. The unique hydrogen uptakes of Ni⁻ and Co-MOF-5 shown in this study pave the way for further improvement in hydrogen uptake. Full article

Metal–organic frameworks (MOFs) have significant potential for hydrogen storage. The main benefit of MOFs is their reversible and high-rate hydrogen adsorption process, whereas their biggest disadvantage is related to their operation at very low temperatures. In this study, we describe selected examples of MOF structures studied for hydrogen adsorption and different factors affecting hydrogen adsorption in MOFs. Approaches to improving hydrogen uptake are reviewed, including surface area and pore volume, in addition to the value of isosteric enthalpy of hydrogen adsorption. Nanoconfinement of metal hydrides inside MOFs is proposed as a new approach to hydrogen storage. Conclusions regarding MOFs with incorporated metal nanoparticles, which may be used as nanoscaffolds and/or H₂ sorbents, are summarized as prospects for the near future. Full article

Hydrogen (H₂) is largely regarded as a potential cost-efficient clean fuel primarily due to its beneficial properties, such as its high energy content and sustainability. With the rising demand for H₂ in the past decades and its favorable characteristics as an energy carrier, the escalating USA consumption of pure H₂ can be projected to reach 63 million tons by 2050. Despite the tremendous potential of H₂ generation and its widespread application, transportation and storage of H₂ have remained the major challenges of a sustainable H₂ economy. Various efforts have been undertaken by storing H₂ in activated carbons, metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc. Recently, the literature has been stressing the need to develop biomass-based activated carbons as an effective H₂ storage material, as these are inexpensive adsorbents with tunable chemical, mechanical, and morphological properties. This article reviews the current research trends and perspectives on the role of various properties of biomass-based activated carbons on its H₂ uptake capacity. The critical aspects of the governing factors of H₂ storage, namely, the surface morphology (specific surface area, pore volume, and pore size distribution), surface functionality (heteroatom and functional groups), physical condition of H₂ storage (temperature and pressure), and thermodynamic properties (heat of adsorption and desorption), are discussed. A comprehensive survey of the literature showed that an “ideal” biomass-based activated carbon sorbent with a micropore size typically below 10 Å, micropore volume greater than 1.5 cm³/g, and high surface area of 4000 m²/g or more may help in substantial gravimetric H₂ uptake of >10 wt% at cryogenic conditions (−196 °C), as smaller pores benefit by stronger physisorption due to the high heat of adsorption. Full article

The removal of hydrogen sulfide (H₂S) from gas streams with varying overall pressure and H₂S concentrations is a long-standing challenge faced by the oil and gas industries. The present work focuses on H₂S capture using metal–organic frameworks (MOFs), in an effort to shed light on their potential as adsorbents in the field of gas storage and separation. MOFs hold great promise as they make possible the design of structures from organic and inorganic units, but also, they have provided an answer to a long-time challenging issue, i.e., how to design extended structures of materials. Moreover, the functionalization of the MOF’s surface can result in increased H₂S uptake. For example, the insertion of 1% of a fluorinated linker in MIL-101(Cr)-4F(1%) allows for enhanced H₂S capture. Although noticeable efforts have been made in studying the adsorption capacity of H₂S using MOFs, there is a clear need for gaining a deeper understanding in terms of their thermal conductivities and specific heats in order to design more stable adsorption beds, experiencing high exothermicity. Simply put, the exothermic nature of adsorption means that sharp rises in temperature can negatively affect the bed stability in the absence of sufficient heat transfer. The work presented herein provides a detailed discussion by thoroughly combining the existing literature on new developments in MOFs for H₂S removal, and tries to provide insight into new areas for further research. Full article

In the field of energy storage, recently investigated nanocomposites show promise in terms of high hydrogen uptake and release with enhancement in the reaction kinetics. Among several, carbonaceous nanovariants like carbon nanotubes (CNTs), fullerenes, and graphitic nanofibers reveal reversible hydrogen sorption characteristics at 77 K, due to their van der Waals interaction. The spillover mechanism combining Pd nanoparticles on the host metal-organic framework (MOF) show room temperature uptake of hydrogen. Metal or complex hydrides either in the nanocomposite form and its subset, nanocatalyst dispersed alloy phases illustrate the concept of nanoengineering and nanoconfinement of particles with tailor-made properties for reversible hydrogen storage. Another class of materials comprising polymeric nanostructures such as conducting polyaniline and their functionalized nanocomposites are versatile hydrogen storage materials because of their unique size, high specific surface-area, pore-volume, and bulk properties. The salient features of nanocomposite materials for reversible hydrogen storage are reviewed and discussed. Full article