Postsynthetically Modified Alkoxide-Exchanged Ni2(OR)2BTDD: Synergistic Interactions of CO2 with Open Metal Sites and Functional Groups

Postsynthetic modifications (PSMs) of metal-organic frameworks (MOFs) play a crucial role in enhancing material performance through open metal site (OMS) functionalization or ligand exchange. However, a significant challenge persists in preserving open metal sites during ligand exchange, as these sites are inherently bound by incoming ligands. In this study, for the first time, we introduced alkoxides by exchanging bridging chloride in Ni2Cl2BTDD (BTDD=bis (1H-1,2,3,-triazolo [4,5-b],-[4',5'-i]) dibenzo[1,4]dioxin) through PSM. Rietveld refinement of synchrotron X-ray diffraction data indicated that the alkoxide oxygen atom bridges Ni(II) centers while the OMSs of the MOF are preserved. Due to the synergy of the existing OMS and introduced functional group, the alkoxide-exchanged MOFs showed CO2 uptakes superior to the pristine MOF. Remarkably, the tert-butoxide-substituted Ni_T exhibited a nearly threefold and twofold increase in CO2 uptake compared to Ni2Cl2BTDD at 0.15 and 1 bar, respectively, as well as high water stability relative to the other exchanged frameworks. Furthermore, the Grand Canonical Monte Carlo simulations for Ni_T suggested that CO2 interacts with the OMS and the surrounding methyl groups of tert-butoxide groups, which is responsible for the enhanced CO2 capacity. This work provides a facile and unique synthetic strategy for realizing a desirable OMS-incorporating MOF platform through bridging ligand exchange.

Enhancing CO2/N2 and CH4/N2 separation performance by salt-modified aluminum-based metal-organic frameworks

The energy-saving separation of CO2/N2 and CH4/N2 in the energy industry facilitates the reduction of greenhouse gas emissions and replenishes energy resources, but is a challenging separation process. The trade-off between adsorption capacity and selectivity of the adsorbents is one of the key bottlenecks in adsorption separation technologies' large-scale application in the above separation task. Herein, we introduced a series of fluoroborate or fluorosilicate salts (Cu(BF4)2, Zn(BF4)2 and ZnSiF6) into the open coordination nitrogen sites of aluminum-based metal-organic frameworks (MOF-253) to create multiple binding sites to simultaneously enhance the adsorption capacity and selectivity for the target gas. By the synergistic adsorption effect of metal ions (Cu2+ or Zn2+) and fluorinated anions (BF4- or (SiF6)2-), the single-component adsorption capacity and selectivity of salt-modified MOF-253 (MOF-253@Cu(BF4)2, MOF-253@Zn(BF4)2 and MOF-253@ZnSiF6) for CO2 and CH4 were effectively improved when compared to pristine MOF-253 at 298 K and 1 bar. In addition, the salt-modified MOF-253 has a moderate adsorption heat (<30 kJ mol-1) which could be rapidly regenerated at low energy by evacuation desorption. As confirmed by the ambient breakthrough experiments of MOF-253 and MOF-253@ZnSiF6, the real separation performance for both CO2/N2 (1/4) and CH4/N2 (1/4) was obviously improved. This work provides a feasible post-modification strategy on uncoordinated sites of the framework to improve adsorption separation performance and promote the development of ideal adsorbents with a view to realizing their application in the energy industry.

Solvent-Directed Construction of a Nanoporous Metal-Organic Framework with Potential in Selective Adsorption and Separation of Gas Mixtures Studied by Grand Canonical Monte Carlo Simulations

In this report, a microporous metal-organic framework of [Ca(TDC)(DMA)]n (1) and a two-dimensional coordination polymer of [Ca(TDC)(DMF)2 ]n (2), (TDC2- =Thiophene-2,5-dicarboxylate, DMA=N, N'-dimethylacetamide and DMF=N, N'-dimethylformamide) based on Ca(II) were designed by the effect of solvent, and X-ray analysis was performed for the single crystals of 1 and 2. Then, compound 1 was synthesized in three different methods and identified with a set of analyses. Compared to other adsorbents, MOFs are widely used in the field of adsorption and separation of various gases due to a series of distinctive features such as diverse and adjustable structures pores with different dimensions, high porosity and surface area with regular distribution of active sites. Therefore, the ability of 1 to uptake single gases (CH4 , CO2 , C2 H2 , H2, and N2 ) and separation of several binary mixtures of gases (CO2 /CH4 , CO2 /N2 , CO2 /H2 and CO2 /C2 H2 ), were investigated using Grand Canonical Monte Carlo simulations. Volumetric and gravimetric adsorption isotherms in various operating conditions, the isosteric heat of adsorption (qst ), the chemical potential for each thermodynamic state, and snapshots during the simulation process were reported in all cases. The results obtained from the adsorption simulation indicate that compound 1 has a high capacity for uptake of H2 (16 mmol g-1 ) and N2 (12.5 mmol g-1 ), CO2 (6.6 mmol g-1 ), C2 H2 (5 mmol g-1 ) and CH4 (1.5 mmol g-1 ) gases at 1 bar. It also performs well in separating CO2 in binary mixtures, which can be attributed to the presence of open metal sites in nodes of 1 and their electrostatic tendency to interact with CO2 containing the higher quadrupole dipole moment compared to other components of the mixture.

Controlling Charge Transport in 2D Conductive MOFs─The Role of Nitrogen-Rich Ligands and Chemical Functionality

Two-dimensional electrically conducting metal-organic frameworks (2D-e-MOFs) have emerged as a class of highly promising functional materials for a wide range of applications. However, despite the significant recent advances in 2D-e-MOFs, developing systems that can be postsynthetically chemically functionalized, while also allowing fine-tuning of the transport properties, remains challenging. Herein, we report two isostructural 2D-e-MOFs: Ni3(HITAT)2 and Ni3(HITBim)2 based on two new 3-fold symmetric ligands: 2,3,7,8,12,13-hexaaminotriazatruxene (HATAT) and 2,3,8,9,14,15-hexaaminotribenzimidazole (HATBim), respectively, with reactive sites for postfunctionalization. Ni3(HITAT)2 and Ni3(HITBim)2 exhibit temperature-activated charge transport, with bulk conductivity values of 44 and 0.5 mS cm-1, respectively. Density functional theory analysis attributes the difference to disparities in the electron density distribution within the parent ligands: nitrogen-rich HATBim exhibits localized electron density and a notably lower lowest unoccupied molecular orbital (LUMO) energy relative to HATAT. Precise amounts of methanesulfonyl groups are covalently bonded to the N-H indole moiety within the Ni3(HITAT)2 framework, modulating the electrical conductivity by a factor of ∼20. These results provide a blueprint for the design of porous functional materials with tunable chemical functionality and electrical response.

A cooperative adsorbent for the switch-like capture of carbon dioxide from crude natural gas

Natural gas constitutes a growing share of global primary energy due to its abundant supply and lower CO₂ emission intensity compared to coal. For many natural gas reserves, CO₂ contamination must be removed at the wellhead to meet pipeline specifications. Here, we demonstrate the potential of the diamine-appended metal–organic framework ee-2–Mg₂(dobpdc) (ee-2 = N,N-diethylethylenediamine; dobpdc⁴⁻ = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) as a next-generation CO₂ capture material for high-pressure natural gas purification. Owing to a cooperative adsorption mechanism involving formation of ammonium carbamate chains, ee-2–Mg₂(dobpdc) can be readily regenerated with a minimal change in temperature or pressure and maintains its CO₂ capacity in the presence of water. Moreover, breakthrough experiments reveal that water enhances the CO₂ capture performance of ee-2–Mg₂(dobpdc) by eliminating “slip” of CO₂ before full breakthrough. Spectroscopic characterization and multicomponent adsorption isobars suggest that the enhanced performance under humid conditions arises from preferential stabilization of the CO₂-inserted phase in the presence of water. The favorable performance of ee-2–Mg₂(dobpdc) is further demonstrated through comparison with a benchmark material for this separation, zeolite 13X, as well as extended pressure cycling. Overall, these results support continued development of ee-2–Mg₂(dobpdc) as a promising adsorbent for natural gas purification.

Diamine-appended metal–organic frameworks can be optimized as adsorbents for pressure-swing purification of crude natural gas. A cooperative CO₂ binding mechanism enables high CO₂ swing capacities and enhanced performance under humid conditions.

B-Doped 2D-InSe as a bifunctional catalyst for CO2/CH4 separation under the regulation of an external electric field

The separation of CO₂ or CH₄ from a CO₂/CH₄ mixture has drawn great attention in relation to solving air pollution and energy shortage issues. However, research into using bifunctional catalysts to separate CO₂ and CH₄ under different conditions is absent. We have herein designed a novel B-doped two-dimensional InSe (B@2DInSe) catalyst, which can chemically adsorb CO₂ with covalent bonds. B@2DInSe can separate CO₂ and CH₄ in different electric fields, which originates from different regulation mechanisms by an electric field (EF) on the electric properties. The hybridization states between CO₂ and B@2DInSe near the Fermi level have experienced gradual localization and eventually merged into a single narrow peak under an increased EF. As the EF further increased, the merged peak shifted towards higher energy states around the Fermi level. In contrast, the EF mainly alters the degree of hybridization between CH₄ and B@2DInSe at states far below the Fermi level, which is different from the CO₂ situation. These characteristics can also lead to perfect linear relationships between the adsorption energies of CO₂/CH₄ and the electric field, which may be beneficial for the prediction of the required EF without large volumes of calculations. Our results have not only provided novel clues for catalyst design, but they have also provided deep understanding into the mechanisms of bifunctional catalysts.

Diamine Functionalization of a Metal-Organic Framework by Exploiting Solvent Polarity for Enhanced CO2 Adsorption

Diamine-appended metal-organic frameworks (MOFs) exhibit exceptional CO₂ adsorption capacities over a wide pressure range because of the strong interaction between basic amine groups and acidic CO₂. Given that their high CO₂ working capacity is governed by solvent used during amine functionalization, a systematic investigation on solvent effect is essential but not yet demonstrated. Herein, we report a facile one-step solvent exchange route for the diamine functionalization of MOFs with open metal sites, using an efficient method to maximize diamine loading. We employed an MOF, Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxido-3,3'-biphenyldicarboxylate), which contains high-density open metal sites. Indirect grafting with N-ethylethylenediamine (een) was performed with a minimal amount of methanol (MeOH) via multiple MeOH exchanges and diamine functionalization, resulting in a top-tier CO₂ adsorption capacity of 16.5 wt %. We established the correlation between N,N-dimethylformamide (DMF) loading and infrared peaks, which provides a simple method for determining the amount of the remaining DMF in Mg₂(dobpdc). All interactions among Mg, DMF, diamine, and solvent were analyzed by van der Waals (vdw)-corrected density functional theory (DFT) calculations to elucidate the effect of chemical potential on diamine grafting.

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal-Organic Frameworks with Kuratowski-Type Building Units

Postsynthetic modification methods have emerged as indispensable tools for tuning the properties and reactivity of metal-organic frameworks (MOFs). In particular, postsynthetic X-type ligand exchange (PXLE) at metal building units has gained increasing attention as a means of immobilizing guest species, modulating the reactivity of framework metal ions, and introducing new functional groups. The reaction of a Zn-OH functionalized analogue of CFA-1 (1-OH, Zn(ZnOH)₄(bibta)₃, where bibta^2- = 5,5'-bibenzotriazolate) with organic substrates containing mildly acidic E-H groups (E = C, O, N) results in the formation of Zn-E species and water as a byproduct. This Brønsted acid-base PXLE reaction is compatible with substrates with pK_a(DMSO) values as high as 30 and offers a rapid and convenient means of introducing new functional groups at Kuratwoski-type metal nodes. Gas adsorption and diffuse reflectance infrared Fourier transform spectroscopy experiments reveal that the anilide-exchanged MOFs 1-NHPh_0.9 and 1-NHPh_2.5 exhibit enhanced low-pressure CO₂ adsorption compared to 1-OH as a result of a Zn-NHPh + CO₂ ⇌ Zn-O₂CNHPh chemisorption mechanism. The MFU-4l analogue 2-NHPh ([Zn₅(OH)_2.1(NHPh)_1.9(btdd)₃], where btdd^2- = bis(1,2,3-triazolo)dibenzodioxin), shows a similar improvement in CO₂ adsorption in comparison to the parent MOF containing only Zn-OH groups.

Bispropylurea bridged polysilsesquioxane: A microporous MOF-like material for molecular recognition

Microporous organosilicas assembled from polysilsesquioxane (POSS) building blocks are promising materials that are yet to be explored in-depth. Here, we investigate the processing and molecular structure of bispropylurea bridged POSS (POSS-urea), synthesised through the acidic condensation of 1,3-bis(3-(triethoxysilyl)propyl)urea (BTPU). Experimentally, we show that POSS-urea has excellent functionality for molecular recognition toward acetonitrile with an adsorption level of 74 mmol/g, which compares favourably to MOFs and zeolites, with applications in volatile organic compounds (VOC). The acetonitrile adsorption capacity was 132-fold higher relative to adsorption capacity for toluene, which shows the pores are highly selective towards acetonitrile adsorption due to their size and arrangement. Theoretically, our tight-binding density functional and molecular dynamics calculations demonstrated that this BTPU based POSS is microporous with an irregular placement of the pores. Structural studies confirm maximal pore sizes of ∼1 nm, with POSS cages possessing an approximate edge length of ∼3.16 Å.

Understanding Correlation Between CO2 Insertion Mechanism and Chain Length of Diamine in Metal-Organic Framework Adsorbents

Although CO₂ insertion is a predominant phenomenon in diamine-functionalized Mg₂ (dobpdc) (dobpdc^4- =4,4-dioxidobiphenyl-3,3'-dicarboxylate) adsorbents, a high-performance metal-organic framework for capturing CO₂ , the fundamental function of the diamine carbon chain length in the mechanism remains unclear. Here, Mg₂ (dobpdc) systems with open metal sites grafted by primary diamines NH₂ -(CH₂ )_n -NH₂ were developed, with en (n=2), pn (n=3), bn (n=4), pen (n=5), hn (n=6), and on (n=8). Based on CO₂ adsorption and IR results, CO₂ insertion is involved in frameworks with n=2 and 3 but not in systems with n≥5. According to NMR data, bn-appended Mg₂ (dobpdc) exhibited three different chemical environments of carbamate units, attributed to different relative conformations of carbon chains upon CO₂ insertion, as validated by first-principles density functional theory (DFT) calculations. For 1-hn and 1-on, DFT calculations indicated that diamine inter-coordinated open metal sites in adjacent chains bridged by carboxylates and phenoxides of dobpdc^4- . Computed CO₂ binding enthalpies for CO₂ insertion (-27.8 kJ mol^-1 for 1-hn and -20.2 kJ mol^-1 for 1-on) were comparable to those for CO₂ physisorption (-19.3 kJ mol^-1 for 1-hn and -20.8 kJ mol^-1 for 1-on). This suggests that CO₂ insertion is likely to compete with CO₂ physisorption on diamines of the framework when n≥5.

Shaping of a Metal-Organic Framework-Polymer Composite and Its CO2 Adsorption Performances from Humid Indoor Air

Diamine-functionalized metal-organic frameworks (MOFs) are known as desirable adsorbents that can capture CO₂ even at low pressures, but the humidity instability of bare MOF powders as well as their shaping have not yet adequately addressed for practical applications. Herein, we report an effective synthetic strategy for fabricating millimeter-sized MOF/poly(vinylidene fluoride) (PVDF) composite beads with different amounts of PVDF binders (30, 40, and 50 wt %) via a phase inversion method, followed by the postfunctionalization of 1-ethylpropane-1,3-diamine (epn). Compared with the pristine MOF powder, the diamine-grafted bead, epn-MOF/PVDF40, upon mixing with 40% binder polymers, exhibited a superior long-term performance without structural collapse for up to 1 month. The existence of the hydrophobic PVDF polymer in the composite material is responsible for such durability. This work provides a promising preparative route toward developing stable and shaped MOFs for the removal of indoor CO₂.

Molecular engineering in a family of pillared-layered metal-organic frameworks for tuning gas adsorption behavior

In this work, inspired by a water-assisted three-dimensional supramolecular structure 1, we use a mixed-ligand strategy to form a 3D pillared-layered matrix by the introduction of linear ligands to compete against the water molecules. The resulting analogue microporous MOFs of 2-H, 2-F and 2-N, decorated with different functional groups, similarly show the CO2 uptake. Thanks to the negligible N2 adsorption capacity, enhanced selective adsorption towards CO2 is achieved in compound 2-N. That is, we present here an alternative plan for the high CO2 selective adsorption performance. In addition, the structure stability and moderate affinity for CO2 of these microporous MOFs endow them with excellent reusability.

Effect of Amine Functionalization of MOF Adsorbents for Enhanced CO2 Capture and Separation: A Molecular Simulation Study

Different types of amine-functionalized MOF structures were analyzed in this work using molecular simulations in order to determine their potential for post-combustion carbon dioxide capture and separation. Six amine models -of different chain lengths and degree of substitution- grafted to the unsaturated metal sites of the M₂(dobdc) MOF [and its expanded version, M₂(dobpdc)] were evaluated, in terms of adsorption isotherms, selectivity, cyclic working capacity and regenerability. Good agreement between simulation results and available experimental data was obtained. Moreover, results show two potential structures with high cyclic working capacities if used for Temperature Swing Adsorption processes: mmen/Mg/DOBPDC and mda-Zn/DOBPDC. Among them, the -mmen functionalized structure has higher CO₂ uptake and better cyclability (regenerability) for the flue gas mixtures and conditions studied. Furthermore, it is shown that more amine functional groups grafted on the MOFs and/or full functionalization of the metal centers do not lead to better CO₂ separation capabilities due to steric hindrances. In addition, multiple alkyl groups bonded to the amino group yield a shift in the step-like adsorption isotherms in the larger pore structures, at a given temperature. Our calculations shed light on how functionalization can enhance gas adsorption via the cooperative chemi-physisorption mechanism of these materials, and how the materials can be tuned for desired adsorption characteristics.

MOF-74-type frameworks: tunable pore environment and functionality through metal and ligand modification

This highlight demonstrates a comprehensive overview of MOF-74-type frameworks in terms of synthetic approaches and pre- or post-synthetic modification approaches.

Boosting gas separation performance and suppressing the physical aging of polymers of intrinsic microporosity (PIM-1) by nanomaterial blending

In recent decades, polymers of intrinsic microporosity (PIMs), especially the firstly introduced PIM-1, have been actively explored for various membrane-based separation purposes and widely recognized as the next generation membrane materials of choice for gas separation due to their ultra-permeable characteristics. Unfortunately, the polymers suffer substantially the negative impacts of physical aging, a phenomenon that is primarily noticeable in high free volume polymers. The phenomenon occurs at the molecular level, which leads to changes in the physical properties, and consequently the separation performance and membrane durability. This review discusses the strategies that have been employed to manage the physical aging issue, with a focus on the approach of blending with nanomaterials to give mixed matrix membranes. A detailed discussion is provided on the types of materials used, their inherent properties, the effects on gas separation performance, and their benefits in the suppression of the aging problem.

Selective adsorption of CO2 from gas mixture by P-decorated C24N24 fullerene assisted by an electric field: A DFT approach

Selective, reversible and tailored adsorption of CO₂ from gas mixture is always demanded to control global warming. We for the first time used P-decorated C₂₄N₂₄ fullerene for selective separation of CO₂ from N₂/CO₂ mixture in the presence of an electric field by using density functional theory methods. The computed geometrical parameters evince that the binding distances and bond angles (OCO) are remarkably reduced in electric field and that transformed the physisorption to chemisorption by increasing the field from 0.012 to 0.013 au. The adsorption/desorption of CO₂ over the substrate can be easily controlled by switching on and off the electric field. This study reveals that P@C₂₄N₂₄ is a selective adsorbent of CO₂ from N₂/CO₂ mixture and will help the future synthesis of selective, controllable and regenerable adsorbent for the CO₂ separation from gas mixture in presence of electric field.

Metal-Organic Framework Adsorbent for Practical Capture of Trace Carbon Dioxide

Control of indoor CO₂ concentration to a safe level is important to human health. Metal-organic-framework-based adsorbents show superior adsorption performance at moderate CO₂ concentration compared to other solid adsorbents but suffer from low capacities and high regeneration temperature at indoor CO₂ concentrations and poor humidity stability. Herein, we report epn-grafted Mg₂(dobpdc) (epn = 1-ethylpropane-1,3-diamine) showing a CO₂ capacity of 12.2 wt % at an acceptable concentration of 1000 ppm and a practically low desorption temperature of 70 °C, which surpasses the performance of conventional solid adsorbents under the given conditions. After poly(dimethylsiloxane) coating, this material reveals a significant adsorption amount (∼10 wt %) in humid conditions (up to 98% relative humidity) with structural durability.

Femto- to Millisecond Time-Resolved Photodynamics of a Double-Functionalized Push-Pull Organic Linker: Potential Candidate for Optoelectronically Active MOFs

The design of improved organic linkers for the further engineering of smarter metal–organic framework (MOF) materials has become a paramount task for a wide number of material scientists. In this report, a luminescent double-functionalized push–pull (electron donor–acceptor) archetype organic molecule, dimethyl 4-amino-8-cyanonaphthalene-2,6-dicarboxylate (Me₂CANADC), has been synthesized and characterized. The optical steady-state properties of Me₂CANADC are strongly influenced by the surrounding environment as a direct consequence of its strong charge transfer (CT) character. The relaxation from its first electronically excited singlet state follows a double pathway: (1) on one side deactivating from its local excited (LE) state in the sub-picosecond or picosecond time domain, and (2) on the other side undergoing an ultrafast intramolecular charge transfer (ICT) reaction that is slowing down in viscous solvents. The deactivation to the ground state of these species with CT character is the origin of the Me₂CANADC luminescence, and they present solvent-dependent lifetime values ranging from 8 to 18 ns. The slow photodynamics of Me₂CANADC unveils the coexistence of a non-emissive triplet excited state and the formation of a long-lived charge separated state (2 µs). These observations highlight the promising optical properties of Me₂CANADC linker, opening a window for the design of new functional MOFs with huge potential to be applied in the fields of luminescent sensing and optoelectronics.

Adsorption Properties and Microscopic Mechanism of CO2 Capture in 1,1-Dimethyl-1,2-ethylenediamine-Grafted Metal-Organic Frameworks

The adsorption properties and microscopic mechanism of CO₂ adsorption in 1,1-dimethyl-1,2-ethylenediamine (dmen) functionalized M₂(dobpdc) (dobpdc^4-=4,4'-dioxidobiphenyl-3,3'-dicarboxylate; M = Mg, Sc-Zn) have been completely unveiled for the first time via comprehensive investigations based on first-principles density functional theory (DFT) calculations. The results show that for the primary-primary amine, dmen prefers to interact with the open metal site of M₂(dobpdc) via the end with smaller steric hindrance. The binding energies of dmen with MOFs are in the range of 104-174 kJ/mol. In presence of CO₂, it fully inserts into the metal-N bond, forming ammonium carbamate. The CO₂ binding energies vary from 53 to 89 kJ/mol, showing strong metal dependence. Among the 11 metals, dmen-Sc₂(dobpdc) and dmen-Mg₂(dobpdc) have the highest CO₂ binding energies of 89 and 84 kJ/mol, respectively, and may have large CO₂ adsorption capacity for practical applications. More importantly, the microscopic CO₂ capture process of dmen-M₂(dobpdc) is revealed at the atomic level. The whole reaction process includes two steps, that is, formation of zwitterion intermediate (step 1) and rearrangement of the zwitterion intermediate (step 2). The first step in which nucleophilic addition between CO₂ and the metal-bound amine and proton transfer from the metal-bound amine to free amine simultaneously occur is a rate-determining step, with higher energy barriers (0.99-1.35 eV). The second step with much lower barriers (maximum of 0.16 eV) is extremely easy, which can promote the whole CO₂ uptake process in dmen-M₂(dobpdc). This study provides a fundamental understanding of the underlying mechanism of the rather complicated CO₂ adsorption process and sheds important insights on design, synthesis, and optimization of highly efficient CO₂ capture materials.

Investigation of CO2 Adsorption on Triethylenetetramine Modified Adsorbents of TETA(n)/Zr-TSCD

In the present study, a new type of material of Zr-TSCD was first synthesized and modified with different amounts of triethylenetetramine (TETA). The properties of the adsorbents were characterised with X-ray diffraction, UV-vis diffuse reflectance spectroscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, N2 adsorption–desorption, energy dispersion spectrum, and thermogravimetric analysis. The results suggested that Zr-TSCD (TSCD=Na3C6H5O7·2H2O) was successfully synthesized through the coordination of Zr atoms from ZrOCl2·8H2O and O species in –COO– groups. After functionalization with TETA, the structure of Zr-TSCD was preserved and the adsorption capacity of CO2 was enhanced dramatically. At 75°C, TETA(30)/Zr-TSCD achieved a maximum absorption capacity of 175.1mg g−1 in a stream of 10mL min−1 CO2. The adsorption capacity ratio of CO2/N2, CO2/O2, and CO2/SO2 was 10.5, 7.4, and 1.2, respectively. In addition, the adsorption capacity of CO2 remained stable during 10 adsorption–desorption cycles.

Synthesis of micro–mesoporous CPO-27-Mg@KIT-6 composites and their test in CO2 adsorption

Novel composites were synthesised through a fusion between CPO-27-Mg framework and mesoporous silica KIT-6 and tested in the CO₂ adsorption.

Three metal–organic framework isomers of different pore sizes for selective CO2 adsorption and isomerization studies

Three MOF isomers including framework-catenation and framework-topological isomers were synthesized for adsorbing carbon dioxide with high selectivity.

Synergistic catalysis of Pd nanoparticles with both Lewis and Bronsted acid sites encapsulated within a sulfonated metal-organic frameworks toward one-pot tandem reactions

The development of a suitable catalytic system in the single catalyst has always been the pursuit for synthetic chemists in order to perform the traditional stepwise reactions in one-pot mode. In this work, an ultra-stable bifunctional catalyst of Pd@MIL-101-SO₃H was successfully constructed and applied in the one-pot oxidation-acetalization reaction whose products have been widely utilized as fuel additives, perfumes, pharmaceuticals and polymer chemistry. The excellent catalytic performance (>99% yields), on the one hand, can be ascribed to the synergistic effects of Pd NPs with both Lewis and Bronsted acid encapsulated within a sulfonated MIL-101(Cr). On the other hand, the exceptionally high capacity of water adsorption in MIL-101(Cr) could promote the equilibrium movement via interrupting the reversible process. More importantly, Pd@MIL-101-SO₃H is recyclable and can be reused for at least 8 times without sacrificing its catalytic activities. As far as we know, this is the first time that a water adsorption enhanced equilibrium movement of reversible reaction by porous catalyst to achieve high yields has been realized in Pd@MIL-101-SO₃H, which may provide an absolutely new and efficient strategy especially for designing reaction-oriented catalysts.

Water Enables Efficient CO2 Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework

Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO₂ emissions. However, the separation of CO₂ from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO₂ partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO₂ strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO₂. High partial pressures of O₂ (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO₂ capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO₂ capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO₂ by a cooperative mechanism that enables access to a large CO₂ cycling capacity with a small temperature swing (2.4 mmol CO₂/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO₂ capture in 2-ampd-Mg₂(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO₂ adsorption, thereby increasing the thermodynamic driving force for CO₂ binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg₂(dobpdc), its high CO₂ adsorption capacity, and its high CO₂ capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.