Present and future of MOF research in the field of adsorption and molecular separation

Molecular Insights into the Correlation between Microstructure and Thermal Conductivity of Zeolitic Imidazolate Frameworks

The thermal conductivity of metal-organic frameworks (MOFs) imposes significant impacts on the thermal transfer performance of related adsorption systems in engineering applications. However, how the structural properties of MOFs affect their thermal conductivities has yet to be unraveled. In this work, the thermal conductivities of 18 zeolitic imidazolate frameworks (ZIFs) were calculated by equilibrium molecular dynamics (MD) simulations. It was revealed that the thermal conductivities of ZIFs were not directly correlated with the commonly investigated structural properties. Thus, two parameters including alignment tensor (A_i) and pathway factor (P_f) were proposed to quantitatively evaluate the orientation and distribution of heat transfer pathways within frameworks, which was demonstrated to correlate better with the thermal conductivities of ZIFs. This study provides new insights into the thermal transfer mechanism within framework-based nanoporous materials, which may also facilitate fundamental understanding and guide the rational design of porous crystals with the thermal conductivity of interest.

Terephthalate and trimesate metal-organic frameworks of Mn, Co, and Ni: exploring photostability by spectroscopy

We report a rapid synthesis for the fabrication of terephthalate and trimesate metal-organic frameworks (MOFs) of Mn, Co, and Ni by ultrasonication of organic linkers with freshly prepared metal hydroxides. The MOFs were characterized by various microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. MOFs with low bandgap energy (1.88-2.73 eV) showed strong absorbance in the UV-visible range. MOFs were exposed to UV irradiation for 40 h to understand their photostability. The MOFs showed decreased surface area and porosity with CoBTC as an exception. PXRD was less convincing for exploring functional changes in the UV-irradiated MOFs. XPS predicted changes in the oxidation states of metal nodes, the degradation of the organic linkers, and decarboxylation process in many of the transition MOFs. The study predicted terephthalate-based MOFs as more photostable than corresponding trimesate-based MOFs. This study is one of the first attempts in exploring photostability of MOFs with Mn, Co, and Ni as nodes.

CO2 adsorption mechanisms on MOFs: a case study of open metal sites, ultra-microporosity and flexible framework

In this review the CO₂ adsorption mechanisms of MOF-74-Mg, HKUST-1, SIFSIX-3-M, and ZIF-8 are explored, highlighting their preferential adsorption sites, CO₂–MOF complex configuration, adsorption dynamics, bonding angle, and water stability.

A Critical Review on Metal-Organic Frameworks and Their Composites as Advanced Materials for Adsorption and Photocatalytic Degradation of Emerging Organic Pollutants from Wastewater

Water-borne emerging pollutants are among the greatest concern of our modern society. Many of these pollutants are categorized as endocrine disruptors due to their environmental toxicities. They are harmful to humans, aquatic animals, and plants, to the larger extent, destroying the ecosystem. Thus, effective environmental remediations of these pollutants became necessary. Among the various remediation techniques, adsorption and photocatalytic degradation have been single out as the most promising. This review is devoted to the compilations and analysis of the role of metal-organic frameworks (MOFs) and their composites as potential materials for such applications. Emerging organic pollutants, like dyes, herbicides, pesticides, pharmaceutical products, phenols, polycyclic aromatic hydrocarbons, and perfluorinated alkyl substances, have been extensively studied. Important parameters that affect these processes, such as surface area, bandgap, percentage removal, equilibrium time, adsorption capacity, and recyclability, are documented. Finally, we paint the current scenario and challenges that need to be addressed for MOFs and their composites to be exploited for commercial applications.

Zeolite-Like Boron Imidazolate Frameworks (BIFs): Synthesis and Application

This review is devoted to discussion of the latest advances in design and applications of boron imidazolate frameworks (BIFs) that are a particular sub-family of zeolite-like metal–organic frameworks family. A special emphasis is made on nanostructured hybrid materials based on BIF matrices and their modern applications, especially in environment remediation and energy conversion.

New Microporous Lanthanide Organic Frameworks. Synthesis, Structure, Luminescence, Sorption, and Catalytic Acylation of 2-Naphthol

New metal-organic frameworks (MOF) with lanthanum(III), cerium(III), neodymium(III), europium(III), gadolinium(III), dysprosium(III), and holmium(III)] and the ligand precursor 1,3,5-tris(4-carboxyphenyl)-2,4,6-trimethylbenzene (H3L) were synthesized under solvothermal conditions. Single crystal x-ray analysis confirmed the formation of three-dimensional frameworks of [LnL(H2O)2]n·xDMF·yH2O for Ln = La, Ce, and Nd. From the nitrogen sorption experiments, the compounds showed permanent porosity with Brunauer-Emmett-Teller (BET) surface areas of about 400 m2/g, and thermal stability up to 500 °C. Further investigations showed that these Ln-MOFs exhibit catalytic activity, paving the way for potential applications within the field of catalysis.

Shaping the Future of Fuel: Monolithic Metal-Organic Frameworks for High-Density Gas Storage

The environmental benefits of cleaner, gaseous fuels such as natural gas and hydrogen are widely reported. Yet, practical usage of these fuels is inhibited by current gas storage technology. Here, we discuss the wide-ranging potential of gas-fuels to revolutionize the energy sector and introduce the limitations of current storage technology that prevent this transition from taking place. The practical capabilities of adsorptive gas storage using porous, crystalline metal-organic frameworks (MOFs) are examined with regard to recent benchmark results and ultimate storage targets in this field. In particular, the industrial limitations of typically powdered MOFs are discussed while recent breakthroughs in MOF processing are highlighted. We offer our perspective on the future of practical, rather than purely academic, MOF developments in the increasingly critical field of environmental fuel storage.

[HPLC using capillary monolithic column molecularly imprinted with composite metal organic frame for enrichment and detection of Ponceau 4R in Carthami flos]

OBJECTIVE

To assess the performance of high-performance liquid chromatography (HPLC) combined with capillary monolithic column molecularly imprinted with metal organic frame (UiO-66-NH₂@MIPs capillary monolithic column) for enrichment, purification and detection of Ponceau 4R in Carthami flos.

METHODS

UiO-66-NH₂@MIPs monolithic columns were prepared via in situ polymerization, and the adsorption properties and morphology of the columns were characterized by HPLC, scanning electron microscopy (SEM) and infrared (IR) spectral analysis. HPLC with the prepared columns was performed for detecting the content of Ponceau 4R in Carthami flos samples.

RESULTS

The UiO-66-NH₂@MIPs system showed a good linearity for detecting Ponceau 4R over the concentration range of 0.1-10.0 μg/mL with a correlation coefficient > 0.9999 and a detection limit (S/N=3) of 2.7×10-4 μg/mL. The mean recovery of Ponceau 4R in Carthami flos samples ranged from 82.60% to 105.56%, and the intra-day and inter-day relative standard deviation (RSD) values ranged from 2.4% to 3.4%. The recycling experiment showed that the system could be reused for sensitive detection of Ponceau 4R in Carthami flos. The capacity of UiO-66-NH₂@MIPs column was 0.178 μg/mg, which was superior to that of other monolithic columns (0.089, 0.080, and 0.111 μg/ mg), demonstrating that the addition of UiO-66-NH₂ increased the adsorption capacity of the system. Under the optimized conditions, the UiO-66-NH₂@MIPs-HPLC system had an enrichment factor of over 73 folds with obviously reduced interference by the impurity peaks.

CONCLUSIONS

The UiO-66-NH₂@MIPs column-HPLC system has much better performance for enrichment, purification and detection of Ponceau 4R in Carthami flos than direct HPLC.

An Optimised Compaction Process for Zr-Fumarate (MOF-801)

We reported a systematic approach aimed at identifying the optimal conditions for compaction of MOF-801, a small-pore zirconium-based metal–organic framework (MOF) containing fumaric acid as the linker, that can be easily synthesised in aqueous medium. Pellets of the MOF were prepared by compressing the powder either in neat form or dry-mixed with binders (sucrose, polyvinylalcohol, polyvinylbutyral) under a range of pressures and for different times. The mechanical stability and durability of the pellets was tested by simple drop tests and shake tests, finding that addition of 5% of polyvinylbutyral was enough to produce highly resilient pellets that did not release significant amounts of powder upon cracking. The crystallinity, textural properties and CO2 adsorption performance of the MOF were successively assessed, observing the least change of the original properties in pellets compressed at 146 MPa for 15 s. Compaction at higher pressures impacted the performance more heavily, with no evident benefit from the mechanical point of view, whereas compression time did not have a relevant effect. The cyclic adsorption behaviour was tested, showing that the pellets retained as much as 90% of the CO2 working capacity, while displaying unaffected sorption kinetics, and 74% of the H2O working capacity.

Regeneration, degradation, and toxicity effect of MOFs: Opportunities and challenges

Metal organic frameworks (MOFs) have been investigated extensively for separation, storage, catalysis, and sensing applications. Nonetheless, problems associated with their toxicity, recycling/reuse/regeneration, and degradation have yet to be addressed as one criterion to satisfy their commercialization. Here, the challenges associated with MOF-based technology have been explored to further expand their practical utility in various applications. We start a brief description of challenges associated with MOF-based technology followed by a critical evaluation of toxicity and need of technical options for regeneration of MOFs. Importantly, diverse techniques/process for reuse and regeneration of MOFs like activation of MOFs by heat, vacuum, solvent exchange, supercritical carbon dioxide (SCCO₂) and other miscellaneous options have been discussed with recent examples. Afterward, we also present an economical aspect and future perspectives of MOFs for real world applications. All in all, we aimed to present opportunities and critical review of the current status of MOF technology with respect to their recycling/reuse/regeneration to consider their environmental impact.

Recent advances on porous organic frameworks for the adsorptive removal of hazardous materials

Environmental pollution is one of the most serious problems facing mankind today, and has attracted widespread attention worldwide. The burgeoning class of crystalline porous organic framework materials, metal-organic frameworks and covalent organic frameworks present promising application potential in areas related to pollution control due to their interesting surface properties. In this review, the literature of the past five years on the adsorptive removal of various hazardous materials, mainly including heavy metal ions, harmful gases, organic dyes, pharmaceutical and personal care products, and radionuclides from the environment by using COFs and MOFs, is summarized. The adsorption mechanisms are also discussed to help understand their adsorption performance and selectivity. Additionally, some insightful suggestions are given to enhance the performance of MOFs and COFs in the adsorptive removal of various hazardous materials.

Activated carbon/metal-organic framework nanocomposite: Preparation and photocatalytic dye degradation mathematical modeling from wastewater by least squares support vector machine

Herein, Kiwi peel activated carbon (AC), Materials Institute Lavoisier (MIL-88B (Fe), and AC/MIL-88B (Fe) composite were synthesized and used as catalysts to degrade Reactive Red 198. The material properties were analyzed by the FTIR, BET-BJH, XRD, FESEM, EDX, TGA, and UV-Vis/DRS. The BET surface area of AC, MIL-88B (Fe) and AC/MIL-88B (Fe) was 1113.3, 150.7, and 199.4 m²/g, respectively. The band gap values (E_g) estimated by Tauc plot method, were obtained 5.06, 4.19 and 3.79 eV for AC, MIL-88B (Fe) and AC/MIL-88B (Fe), respectively. The results indicated that the AC/MIL-88B (Fe) composite had higher photocatalytic activity (99%) than that of pure AC (79%) and MIL-88B (Fe) catalysts (87%). The decolorization kinetic was matched well with the second-order model. Moreover, the data were modeled using least squares support vector machine which optimized with Cuckoo optimization algorithm. The optimal parameters were found 0.837 and 3.49e+02 based on σ² and γ values, respectively. The mean square error (MSE) and correlation coefficient (R²) values were obtained 3.97 and 0.948. Therefore, the attained data, materials characterization and prediction of modeling validate the composite form of MIL-88B(Fe) with new AC, had better photocatalytic activity in comparison with the individual form.

Robust synthesis routes and porosity of the Al-based metal–organic frameworks Al-fumarate, CAU-10-H and MIL-160

We confirm that the investigated Al-MOFs are robust with respect to reproducible synthesis and concomitant porosity as a prerequisite for applications.