Synthesis and Characterization of Covalent Triazine Framework CTF-1@Polysulfone Mixed Matrix Membranes and Their Gas Separation Studies

Covalent triazine framework CTF-1 and polysulfone (PSF) are used to form mixed-matrix membranes (MMMs) with 8, 16, and 24 wt% of the porous filler material CTF-1. Studies on permeability and selectivity are carried out concerning the gases O2, N2, CO2, and CH4. CO2 permeability of the synthesized MMMs increases by 5.4 Barrer in comparison to the pure PSF membrane. The selectivity remains unchanged for O2/N2 and CO2/CH4 but was found to be increased for CO2/N2. Further, comparisons to theoretical models for permeability prediction yield a permeability for CTF-1 which is about six times higher than the permeability of PSF. The inverse of the sum of the free fractional volumes (FFV) of the polymer and the filler correlate linearly to the logarithm of the permeabilities of the gases which conversely indicates that the porosity of the filler contributes to the gas transport through the membrane

Mixed-Matrix Membranes of the Air-Stable MOF‑5 Analogue [Co₄(μ₄‑O)(Me₂pzba)₃] with a Mixed-Functional Pyrazolate-Carboxylate Linker for CO₂/CH₄ Separation

The synthesis of the isostructural MOF-5 analogue 3D-[Co₄(μ₄-O)­(Me₂pzba)₃] with the bi- or mixed-functional pyrazolate-carboxylate linker was improved by the use of microwave heating instead of previously described conventional thermal heating, giving a higher yield at drastically shorter reaction time with nearly doubled BET surface area, smaller size, and less aggregation. The significantly increased air/moisture stability of [Co₄(μ₄-O)­(Me₂pzba)₃] compared to MOF-5 made the Co-MOF amenable for the preparation of moisture-tolerant [Co₄(μ₄-O)­(Me₂pzba)₃]/Matrimid mixed-matrix membranes (MMMs) without the use of inert conditions. Uniformly embedding of the small metal–organic framework (MOF) particles was achieved in the polymer, without aggregation and with good MOF–polymer compatibility. [Co₄(μ₄-O)­(Me₂pzba)₃]/Matrimid MMMs exhibited an improved CO₂/CH₄ separation performance over neat Matrimid membranes with an increase in mixed-gas selectivity from 41 for Matrimid to 60 for the 24 wt % MMM at 3 bar transmembrane pressure, which is also higher than reported for moisture-sensitive MOF-5/Matrimid MMMs (maximal <i>S</i> = 45)

Comparative Evaluation of Different MOF and Non‐MOF Porous Materials for SO2 Adsorption and Separation Showing the Importance of Small Pore Diameters for Low‐Pressure Uptake

The search for adsorbents for flue gas desulfurization processes is a current interest. For the first time, a comparative experimental study of SO2 adsorption by porous materials including the prototypical metal–organic frameworks NH2‐MIL‐101(Cr), Basolite F300 (Fe‐1,3,5‐BTC), HKUST‐1 (Cu‐BTC), the zeolitic imidazolate frameworks (ZIF)‐8, ZIF‐67, the alumosilicate Zeolite Y, the silicoaluminumphosphate (SAPO)‐34, Silica gel 60, the covalent triazine framework (CTF)‐1, and the active carbon Ketjenblack is carried out. Microporous materials with pore sizes in the range of 4–8 Å or with nitrogen heterocycles are found to be optimal for SO2 uptake in the low‐pressure range. The SO2 uptake capacity at 1 bar correlates with the Brunauer‐Emmett‐Teller‐surface area and pore volume rather independently of the surface microstructure. Zeolite Y and SAPO‐34 are stable toward humid SO2. The materials Zeolite Y and CTF‐1(600) show the most promising SO2/CO2 selectivity results with an ideal adsorbed solution theory selectivity in the range of 265–149 and 63–43 with a mole fraction of 0.01–0.5 SO2, respectively, at 293 K and 1 bar.Microporous materials with pore sizes in the range of ≈4–8 Å and with nitrogen heterocycles are optimal for the uptake of SO2 in the ‰ range

Encapsulation of a Porous Organic Cage into the Pores of a Metal–Organic Framework for Enhanced CO₂ Separation

We present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient-wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO₂ affinity were successfully encapsulated into the nanospace of Cr-based MIL-101 while retaining the crystal framework, morphology, and high stability of MIL-101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL-101, more affinity sites for CO₂ are created in the resulting CB6@MIL-101 composites, leading to enhanced CO₂ uptake capacity and CO₂/N₂, CO₂/CH₄ separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications

High performance MIL-101(Cr)@6FDA-mPD and MOF-199@6FDA-mPD mixed-matrix membranes for CO2/CH4 separation

Combination of the polyimide 6FDA-mPD (6FDA = 4,4′-hexafluoroisopropylidene diphthalic anhydride and mPD = m-phenylenediamine) and crystallites of the metal–organic frameworks (MOFs) MIL-101(Cr) or MOF-199 (HKUST-1, Cu-BTC) produces mixed-matrix membranes (MMMs) with excellent dispersion and compatibility of the MOF particles within the polymer matrix. Permeation tests of a binary CO2/CH4 (50/50) gas mixture showed a remarkable increase of CO2 permeabilities for MIL-101(Cr)@6FDA-mPD and significantly higher selectivities for MOF-199@6FDA-mPD. The CO2 permeability increased from 10 (neat polymer) to 50 Barrer for the 24 wt% MIL-101(Cr)@6FDA-mPD membrane (with essentially constant selectivity) due to the high pore volume of MIL-101(Cr). The CO2/CH4 selectivity increased from 54 to 89 from the neat 6FDA-mPD polymer to the 24 wt% MOF-199@6FDA-mPD membrane, apparently due to the high CO2 adsorption capacity of MOF-199.Financial support (MAT2013-40556-R) from the Ministry of Economy and Competitiveness (MINECO) is gratefully acknowledged by JC. The work of CJ was supported by the Federal German Ministry of Education and Research (BMBF) under grant Optimat 03SF0492C.Peer reviewe

Covalent Triazine Frameworks Based on the First Pseudo-Octahedral Hexanitrile Monomer via Nitrile Trimerization: Synthesis, Porosity, and CO2 Gas Sorption Properties

Herein, we report the first synthesis of covalent triazine-based frameworks (CTFs) based on a hexanitrile monomer, namely the novel pseudo-octahedral hexanitrile 1,4-bis(tris(4′-cyano-phenyl)methyl)benzene 1 using both ionothermal reaction conditions with ZnCl2 at 400 °C and the milder reaction conditions with the strong Brønsted acid trifluoromethanesulfonic acid (TFMS) at room temperature. Additionally, the hexanitrile was combined with different di-, tri-, and tetranitriles as a second linker based on recent work of mixed-linker CTFs, which showed enhanced carbon dioxide captures. The obtained framework structures were characterized via infrared (IR) spectroscopy, elemental analysis, scanning electron microscopy (SEM), and gas sorption measurements. Nitrogen adsorption measurements were performed at 77 K to determine the Brunauer-Emmett-Teller (BET) surface areas range from 493 m2/g to 1728 m2/g (p/p0 = 0.01–0.05). As expected, the framework CTF-hex6 synthesized from 1 with ZnCl2 possesses the highest surface area for nitrogen adsorption. On the other hand, the mixed framework structure CTF-hex4 formed from the hexanitrile 1 and 1,3,5 tricyanobenzene (4) shows the highest uptake of carbon dioxide and methane of 76.4 cm3/g and 26.6 cm3/g, respectively, at 273 K