Does Mixed Linker-Induced Surface Heterogeneity Impact the Accuracy of IAST Predictions in UiO-66-NH2?

To move toward more energy-efficient adsorption-based processes, there is a need for accurate multicomponent data under realistic conditions. While the Ideal Adsorbed Solution Theory (IAST) has been established as the preferred prediction method due to its simplicity, limitations and inaccuracies for less ideal adsorption systems have been reported. Here, we use amine-functionalized derivatives of the UiO-66 structure to change the extent of homogeneity of the internal surface toward the adsorption of the two probe molecules carbon dioxide and ethylene. Although it might seem plausible that more functional groups lead to more heterogeneity and, thus, less accurate predictions by IAST, we find a mixed-linker system with increased heterogeneity in terms of added adsorption sites where IAST predictions and experimental loadings agree exceptionally well. We show that incorporating uncertainty analysis into predictions with IAST is important for assessing the accuracy of these predictions. Energetic investigations combined with Grand Canonical Monte Carlo simulations reveal almost homogeneous carbon dioxide but heterogeneous ethylene adsorption in the mixed-linker material, resulting in local, almost pure phases of the individual components.

Surprising Use of the Business Innovation Bass Diffusion Model To Accurately Describe Adsorption Isotherm Types I, III, and V

Using adsorption isotherm data to determine heats of adsorption or predict mixture adsorption using the ideal adsorbed solution theory (IAST) relies on accurate fits of the data with continuous, mathematical models. Here, we derive an empirical two-parameter model to fit isotherm data of IUPAC types I, III, and V in a descriptive way based on the Bass model for innovation diffusion. We report 31 isotherm fits to existing literature data covering all six types of isotherms, various adsorbents, such as carbons, zeolites, and metal-organic frameworks (MOFs), as well as different adsorbing gases (water, carbon dioxide, methane, and nitrogen). We find several cases, especially for flexible MOFs, where previously reported isotherm models reached their limits and either failed to fit the data or could not sufficiently be fitted due to stepped type V isotherms. Moreover, in two instances, models specifically developed for distinct systems are fitted with a higher R² value compared to the models in the original reports. Using these fits, it is demonstrated how the new Bingel-Walton isotherm can be used to qualitatively assess the hydrophilic or hydrophobic behavior of porous materials from the relative magnitude of the two fitting parameters. The model can also be employed to find matching heats of adsorption values for systems with isotherm steps using one, continuous fit instead of partial, stepwise fits or interpolation. Additionally, using our single, continuous fit to model stepped isotherms in IAST mixture adsorption predictions leads to good agreement with the results from the osmotic framework adsorbed solution theory that was specifically developed for these systems using a stepwise, approximate fitting, which is yet far more complex. Our new isotherm equation accomplishes all of these tasks with only two fitted parameters, providing a simple, accurate method for modeling a variety of adsorption behavior.

Strategies for CO2 capture: positive and negative feature

Carbon dioxide is one of the primary greenhouse gases affecting climate change and global warming. Thus, capturing carbon dioxide (CO2) has always been a significant issue in the environmental industry. Numerous procedures have been used to remove acid and natural gas from the flue. This review aims to illustrate and discuss the primary CO2 capture technologies, such as adsorption, absorption, and membrane separation. Moreover, the development of every technology.

Metal-organic framework structures of fused hexagonal motifs with cuprophilic interactions of a triangular Cu(I)3(pyrazolate-benzoate) metallo-linker

The reaction of the N,O-heteroditopic bifunctional ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid (H2mpba) with Cu(NO3)2·2.5H2O and Zn(NO3)2·4H2O or Zn(CH3COO)2·2H2O in N,N-dimethylformamide (DMF) results in concomitant formation of three bimetallic metal-organic frameworks (MOFs) with...

Porous Metal-Organic Polyhedra: Morphology, Porosity, and Guest Binding

Designing porous materials which can selectively adsorb CO₂ or CH₄ is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO₂ and CH₄ using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO₂ and CH₄ in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO₂ molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO₂. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.

We report a family of metal−organic polyhedra (MOP), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analysis. A detailed structural investigation into the adsorption of CO₂ and CH₄ is reported using in situ X-ray and neutron diffraction, coupled with DFT calculations.

Novel Metal-Organic Framework-Based Photocrosslinked Hydrogel System for Efficient Antibacterial Applications

Metal-organic frameworks (MOFs) can be applied in biology and medicine as drug delivery systems by carrying drugs on their surfaces or releasing bioactive ligands. To investigate the therapeutic potential of hydrogels that contain MOFs, three MOFs containing glutarate and 1,2-bis(4-pyridyl)ethylene ligands were synthesized by the previously reported hydrothermal or solvothermal reactions: Cu-MOF 1, Co-MOF 2, and Zn-MOF 3. Bioactive MOF-embedded hydrogels (hydrogel@Cu-MOF 1, hydrogel@Co-MOF 2, and hydrogel@Zn-MOF 3) were prepared by UV light-mediated thiol-ene photopolymerization using diacrylated polyethylene glycol (PEG), 4-arm-thiolated PEG, and MOFs. The activities of the MOF-embedded hydrogels were tested against the Gram-negative bacterium Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. These MOF-embedded hydrogels were observed to be very stable, based on the release test of M^II ions, and both hydrogel@Cu-MOF 1 and hydrogel@Co-MOF 2 showed excellent antibacterial activity. Although, in human dermal fibroblasts, hydrogel@Cu-MOF 1 showed no cytotoxic effects, it exhibited 99.9% antibacterial effects at the minimum bactericidal concentration. Physical properties such as the surface area and dimension of MOFs with different central metals appeared to be more important than the chemical properties of the ligands in determining the effects on bacteria. These MOF-embedded hydrogels may be useful in antibacterial applications such as cosmetics, treatment of skin diseases, and drug delivery owing to their low cytotoxicity and high bactericidal activity.

Increase of network hydrophilicity from sql to lvt supramolecular isomers of Cu-MOFs with the bifunctional 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate linker

A slight difference in the H-bonding of the linker pyrazole-NH group changes the framework hydrophilicity drastically.

Antibacterial activities of Cu-MOFs containing glutarates and bipyridyl ligands

Metal-organic frameworks (MOFs) can be utilized as antibacterial agents due to their effective antibacterial activities. Four three-dimensional (3D) Cu-MOFs formulated as [Cu₂(Glu)₂(μ-L)]·x(H₂O) (Glu is glutarate, and L is bpy = 4,4'-bipyridine (1), bpa = 1,2-bis(4-pyridyl)ethane (2), bpe = 1,2-bis(4-pyridyl)ethylene (3), and bpp = 1,2-bis(4-pyridyl)propane (4)) were synthesized by hydrothermal reactions or modified literature methods. Their solid-state structures were slightly modified to increase their hydrolytic stabilities in aqueous solution. Despite the seemingly sufficient void spaces in all the solvent-free MOFs, only the thermally activated form of MOF 2 displayed selective gas uptake ability for CO₂ over N₂ and H₂. The antibacterial activities of the four Cu-MOFs, 1, 2, 3, and 4, were investigated by determining their minimal bactericidal concentration (MBC) values against five strains of bacteria, including E. coli, S. aureus, K. pneumonia, P. aeruginosa, and MRSA, which can be easily met in our daily surrounding environments. Although these Cu-MOFs were found to be structurally very stable in aqueous medium during antibacterial activity tests, they exhibited excellent antibacterial activities against all five kinds of bacteria, including Gram-positive bacteria (S. aureus and MRSA) and Gram-negative bacteria (E. coli, K. pneumonia, and P. aeruginosa), with very low MBCs. The robust 3D frameworks with surface active metal sites rather than the small amount of leached Cu^II ions may participate more strongly in inactivating various kinds of bacteria and reduce potential cytotoxicity mainly caused by leached metal ions.

Synthesis and Characterization of an SWCNT@HKUST-1 Composite: Enhancing the CO2 Adsorption Properties of HKUST-1

Synthesis of a new HKUST-1 composite based on single-walled carbon nanotubes (SWCNTs) was successfully achieved (SWCNT@HKUST-1). SWCNTs were used as templates to grow rod-like HKUST-1 crystals over the surface of the nanotubes. N₂ adsorption properties showed an increment on the surface area and pore volume for the SWCNT@HKUST-1 composite. Furthermore, the CO₂ capture increased, from 7.92 to 8.75 mmol g^-1 at 196 K up to 100 kPa, for the SWCNT@HKUST-1 composite. This enhancement was directly associated with the increase of the surface area of the composite. Additionally, an increase in the CO₂ heat of adsorption was estimated, from 30 to 39.1 kJ mol^-1 for the SWCNT@HKUST-1 composite. In situ Raman experiments corroborated the favored CO₂ adsorption for the composite and provided an insight into the augmented hydrophobicity of the SWCNT@HKUST-1. Ethanol adsorption isotherms corroborated an increase in the hydrophobicity of the material upon the incorporation of carbon nanotubes.

Direct Catalytic Conversion of CO2 to Cyclic Organic Carbonates under Mild Reaction Conditions by Metal—Organic Frameworks

The reduction of the representative greenhouse gas, carbon dioxide (CO2), is significantly an important theme for the current research in the modern chemical world. For the last two decades, the development of new metal-organic framework (MOF) systems with highly selective capture of CO2, in the presence of other competing gaseous molecules, has flourished to capture or separate CO2 for environmental protection. Nonetheless, the ultimate resolution to lessen the atmospheric CO2 concentration may be in the chemical or electrochemical conversion of CO2 to other compounds. In this context, the catalytic cycloaddition reaction of CO2 into organic epoxides to produce cyclic carbonates is a more attractive method. MOFs are being proven as efficient heterogeneous catalytic systems for this important reaction. In this review, we collected very recent progress in MOF-based catalytic systems, fully operable under very mild reaction conditions (room temperature and 1 atm CO2).

Salen-Based Metal Complexes and the Physical Properties of their Porous Organic Polymers

Porous organic polymers (POPs) represent interesting candidate materials for carbon dioxide (CO2) adsorption applications owing to the permanently porous nature of the structures and the ability to vary metalloligand centres that can be incorporated as a potential means of property tuning. This work reports the synthesis and characterisation of four transition metal complexes (using M=Mn, Ni, Fe, and Pd) of the bis-bromo salen ligand, and the incorporation of these complexes into POPs with tris-(p-ethynyl)-triphenylamine to yield metallated polymers (POPMn, POPNi, POPFe, and POPPd). The POPs were shown to possess Brunauer–Emmett–Teller (BET) surface areas of up to 650m2g−1. Overall, this work provides further insight into the potential of permanently porous polymeric materials in post-combustion capture applications.

Use of a Metal Organic Framework for the Adsorptive Removal of Gaseous HCl: A New Approach for a Challenging Task

In this work, the potentialities of the amino-functionalized, chromium-based MIL-101 metal organic framework (NH₂-MIL-101) as a high capacity, fully regenerable hydrogen chloride adsorbent have been proved by a thorough adsorption thermodynamics investigation. The chosen adsorbent showed high gaseous HCl adsorption capacities and, to the best of our knowledge, it is the first example of a totally regenerable substrate for this kind of adsorbate, as evidenced by both experimental and modeling results. This paves the way to the implementation of greener, more energetically efficient pressure/temperature swing adsorption processes to purify biogas feeds for high-temperature fuel cells.

Green applications of metal–organic frameworks

MOFs as green materials – a highlight of the environmentally conscious or “green” applications of MOFs.

Electroactive Co(iii) salen metal complexes and the electrophoretic deposition of their porous organic polymers onto glassy carbon

This paper reports the CO₂ electroreduction properties of three bis-bromo Co(iii) salen metal complexes and their Porous Organic Polymers (POPs) as a platform for using the salen core as a multi-electron reducing agent. Although Co(iii) salen metal complexes have been studied extensively for their chemical catalysis with CO₂, their electrochemical behaviour, particularly their reduction, in the presence of CO₂ is much less explored. The discrete Co(iii) complexes enabled the reduction of CO₂ to CO in faradaic efficiencies of up to 20%. The reductive electrochemical processes of Co(iii) salen complexes are relatively unknown; therefore, the mechanism of reduction for the complexes was investigated using IR and UV-Vis-NIR spectroelectrochemical (SEC) techniques. The discrete bis-bromo salen complexes were incorporated into POPs with tris-(p-ethynyl)-triphenylamine as a co-ligand and were characterised using solid state NMR, IR, UV-Vis-NIR and Field Emission Scanning Electron Microscopy (FE-SEM). The POP materials were electrophoretically deposited onto glassy carbon under milder conditions than those previously reported in the literature. Direct attachment of the POP materials to glassy carbon enabled improved solid state electrochemical analysis of the samples. The POP materials were also analysed via SEC techniques, where a Co(ii/i) process could be observed, but further reductions associated with the imine reduction compromised the stability of the POPs.

We report the synthesis, characterisation and electrochemistry of Co(iii) salen metal complexes and their porous organic polymers for CO₂ electroreduction.

An In-Depth Structural Study of the Carbon Dioxide Adsorption Process in the Porous Metal-Organic Frameworks CPO-27-M

The CO₂ adsorption process in the family of porous metal-organic framework materials CPO-27-M (M=Mg, Mn, Co, Ni, Cu, and Zn) was studied by variable-temperature powder synchrotron X-ray diffraction under isobaric conditions. The Rietveld analysis of the data provided a time-lapse view of the adsorption process on CPO-27-M. The results confirm the temperature-dependent order of occupation of the three adsorption sites in the pores of the CPO-27-M materials. In CPO-27-M (M=Mg, Mn, Co, Ni, and Zn), the adsorption sites are occupied in sequential order, primarily because of the high affinity of CO₂ for the open metal sites. CPO-27-Cu deviates from this stepwise mechanism, and the adsorption sites at the metal cation and the second site are occupied in parallel. The temperature dependence of the site occupancy of the individual CO₂ adsorption sites derived from the diffraction data is reflected in the shape of the volumetric sorption isotherms. The fast kinetics and high reversibility observed in these experiments support the suitability of these materials for use in temperature- or pressure-swing processes for carbon capture.

Coordination polymers from a flexible alkyldiamine-derived ligand

A traditionally good chelating motif, propanediamine, has been incorporated into a robust coordination framework with vacant amine sites.

Photoactive and Physical Properties of an Azobenzene-Containing Coordination Framework

A new three-dimensional coordination framework, [Zn4(tbazip)3(bpe)2(OH)2]·bpe·{solvent} (where bpe = 1,2-di(4-pyridyl)ethene) containing the novel photoactive ligand tbazip (tbazip = 5-((4-tert-butyl)phenylazo)isophthalic acid) has been synthesised and crystallographically characterised. The photoactivity of discrete tbazip was investigated and compared with its photoactivity while incorporated within the framework. The effect of isomerisation of the incorporated azobenzene on the chemical and physical properties of the framework were investigated using UV-vis and Raman spectroscopies. The framework is porous only to hydrogen gas at 77 K, but displayed an appreciable uptake for CO2 at 195 K.

Tuning the properties of the metal–organic framework UiO-67-bpy via post-synthetic N-quaternization of pyridine sites

N-Quaternization of pyridine sites in UiO-67-bpy affords a cationic MOF UiO-67-bpy-Me with faster and improved anionic dye and CO₂adsorption, and extended visible-light absorption properties, which make UiO-67-bpy-Me more efficient in photodegrading organic dyes.

Exploiting redox activity in metal–organic frameworks: concepts, trends and perspectives

This feature article highlights latest developments in experimental, theoretical and computational concepts relevant to redox-active metal–organic Frameworks.

Enhanced CO2 adsorption on Al-MIL-53 by introducing hydroxyl groups into the framework

Substitution of 25% of terephthalic acid with 2,5-dihydroxyl terephthalic acid in Al-MIL-53 enhances the isosteric heat of CO₂ adsorption remarkably, obtaining a 5.5 wt% CO₂ uptake at 298 K and 0.2 bar.

An indirect generation of 1D MII-2,5-dihydroxybenzoquinone coordination polymers, their structural rearrangements and generation of materials with a high affinity for H2, CO2 and CH4

1D coordination polymers undergo transformations upon desolvation to yield sorbent materials.

Tuning the target composition of amine-grafted CPO-27-Mg for capture of CO2 under post-combustion and air filtering conditions: a combined experimental and computational study

A computational and experimental study is performed to determine the optimal composition that enhances the adsorption performance at low pressure.

The first example of a zirconium-oxide based metal–organic framework constructed from monocarboxylate ligands

This work reports the first example of a Zr-based MOF which is exclusively constructed from the monocarboxylate ligand formate.

Tuning the cavities of zirconium-based MIL-140 frameworks to modulate CO2adsorption

A combined experimental and computational study on the CO₂adsorption performance of zirconium-based MIL-140 frameworks has revealed the crucial influence of pore-confinement effects.