A new microporous metal-organic framework with a novel trinuclear nickel cluster for selective CO2 adsorption

Low temperature and facile synthesis of nitrogen-doped hierarchical porous carbon derived from waste polyethylene terephthalate for efficient CO2 capture

Waste polyethylene terephthalate (PET) with high carbon content (>60 wt%) has shown great potential in the field of synthesizing carbon materials for CO2 capture, attracting increasing attention. Herein, an innovative strategy was proposed to synthesize nitrogen-doped hierarchical porous carbon (PC) for CO2 capture using PET as precursor and sodium amide (NaNH2) as both nitrogen dopant and low-temperature activator. As-synthesized N-doped PC exhibited a significantly high micropore volume of 0.755 cm3/g and a rich content of N- and O-containing functional groups, offering ample active sites for CO2 molecules. Further, the adsorbents demonstrated excellent CO2 capture capacity, achieving 5.7 mmol/g (0 °C) and 3.3 mmol/g (25 °C) at 1 bar, respectively. This was primarily attributed to the synergistic effect of narrow micropores filling and electrostatic interactions. Moreover, as-synthesized PC exhibited rapid CO2 adsorption capability, and its dynamic adsorption process was effectively described using a pseudo-second-order kinetic model. After five consecutive cycles, PET-derived PC still maintained ~100 % of adsorption capacity. They also possessed good CO2/N2 selectivity and reasonable isosteric heat of adsorption. Therefore, as-synthesized nitrogen-doped PC is a promising CO2 adsorbent through low-temperature activation of carbonized PET with NaNH2. Such findings have substantial implications for waste plastic recycling and mitigating the greenhouse effect.

Pyrazine-cored covalent organic frameworks for efficient CO2 adsorption and removal of organic dyes

The rational introduction of nitrogen heterocycles to a linker of covalent organic frameworks (COFs) can effectively capture CO2 and remove dyes in sewage. Here we report the designed synthesis of...

Tailoring Amine-Functionalized Ti-MOFs via a Mixed Ligands Strategy for High-Efficiency CO2 Capture

Amine-functionalized metal-organic frameworks (MOFs) are a promising strategy for the high-efficiency capture and separation of CO₂. In this work, by tuning the ratio of 1,3,5-benzenetricarboxylic acid (H₃BTC) to 5-aminoisophthalic acid (5-NH₂-H₂IPA), we designed and synthesized a series of amine-functionalized highly stable Ti-based MOFs (named MIP-207-NH₂-n, in which n represents 15%, 25%, 50%, 60%, and 100%). The structural analysis shows that the original framework of MIP-207 in the MIP-207-NH₂-n (n = 15%, 25%, and 50%) MOFs remains intact when the mole ratio of ligand H₃BTC to 5-NH₂-H₂IPA is less than 1 to 1 in the resulting MOFs. By the introduction of amino groups, MIP-207-NH₂-25% demonstrates outstanding CO₂ capture performance up to 3.96 and 2.91 mmol g^-1, 20.7% and 43.3% higher than those of unmodified MIP-207 at 0 and 25 °C, respectively. Furthermore, the breakthrough experiment indicates that the dynamic CO₂ adsorption capacity and CO₂/N₂ separation factors of MIP-207-NH₂-25% are increased by about 25% and 15%, respectively. This work provides an additional strategy to construct amine-functionalized MOFs with the maintenance of the original MOF structure and high performance of CO₂ capture and separation.

A new tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-propionic acid: crystal structures of two triclinic polymorphs and of two potassium-organic frameworks

Two polymorphs of the title tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene))tetra-kis-(sulfanedi-yl]}tetra-propionic acid, C20H28N2O8S4, (H4L1), have been obtained, H4L1_A and H4L1_B. Each structure crystallized with half a mol-ecule in the asymmetric unit of a triclinic P unit cell. The whole mol-ecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of H4L1_B were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the -CH2-S-CH2-CH2- side chains compared to those in polymorph H4L1_A. In the crystal of H4L1_A, mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, enclosing R 2 2(8) ring motifs forming layers parallel to plane (100), which are linked by C-H⋯O hydrogen bonds to form a supra-molecular framework. In the crystal of H4L1_B, mol-ecules are also linked by two pairs of O-H⋯O hydrogen bonds enclosing R 2 2(8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the a-axis. Reaction of H4L1 with Hg(NO3)2 in the presence of a potassium acetate buffer did not produce the expected binuclear complex, instead crystals of a potassium-organic framework were obtained, poly[(μ-3-{[(3,5,6-tris-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazin-2-yl)meth-yl]sulfan-yl}propano-ato)potassium], [K(C20H27N2O8S4)] n (KH3L1). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carb-oxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO3)2 resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3'-{[(3,6-bis-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazine-2,5-di-yl)bis(methyl-ene)]bis-(sulfanedi-yl)}dipropionato)dipotassium], [K2(C20H26N2O8S4)] n (K2H2L1). Here, the organic di-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. Two symmetry-related acid groups are deprotonated and the charges are compensated for by two potassium ions.

Crystal structures and Hirshfeld surface analyses of two new tetra-kis-substituted pyrazines and a degredation product

The two new tetra-kis-substituted pyrazines, 1,1',1'',1'''-(pyrazine-2,3,5,6-tetra-yl) tetra-kis-(N,N-di-methyl-methanamine), C16H32N6, (I) and N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline), C36H40N6, (II), both crystallize with half a mol-ecule in the asymmetric unit; the whole mol-ecules are generated by inversion symmetry. There are weak intra-molecular C-H⋯N hydrogen bonds present in both mol-ecules and in (II) the pendant N-methyl-aniline rings are linked by a C-H⋯π inter-action. The degredation product, N,N'-[(6-phenyl-6,7-di-hydro-5H-pyrrolo-[3,4-b]pyrazine-2,3-di-yl)bis(methyl-ene)]bis-(N-methyl-aniline), C28H29N5, (III), was obtained several times by reacting (II) with different metal salts. Here, the 6-phenyl ring is almost coplanar with the planar pyrrolo-[3,4-b]pyrazine unit (r.m.s. deviation = 0.029 Å), with a dihedral angle of 4.41 (10)° between them. The two N-meth-yl-aniline rings are inclined to the planar pyrrolo-[3,4-b]pyrazine unit by 88.26 (10) and 89.71 (10)°, and to each other by 72.56 (13)°. There are also weak intra-molecular C-H⋯N hydrogen bonds present involving the pyrazine ring and the two N-methyl-aniline groups. In the crystal of (I), there are no significant inter-molecular contacts present, while in (II) mol-ecules are linked by a pair of C-H⋯π inter-actions, forming chains along the c-axis direction. In the crystal of (III), mol-ecules are linked by two pairs of C-H⋯π inter-actions, forming inversion dimers, which in turn are linked by offset π-π inter-actions [inter-centroid distance = 3.8492 (19) Å], forming ribbons along the b-axis direction.

Two zinc metal-organic framework isomers based on pyrazine tetracarboxylic acid and dipyridinylbenzene for adsorption and separation of CO2 and light hydrocarbons

Two highly porous metal-organic framework isomers Zn₂(TCPP)(DPB) (1 and 2, H₄TCPP = 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine and DPB = 1,4-di(pyridin-4-yl)benzene) were successfully synthesized using different solvents and acid species to adjust the topologies of these two MOFs. Both of them were constructed by paddlewheel Zn₂(COO)₄, TCPP^4-, and DPB ligands. In compound 1, the Zn₂(COO)₄ paddlewheel units were fitted together by the TCPP^4- ligands to form two-dimensional layers, which were further connected by DPB ligands as pillars to construct a two-fold catenated 3D framework. In compound 2, the cross-linkage of Zn₂(COO)₄ paddlewheel units and TCPP^4- ligands resulted in a three-dimensional framework of Zn-TCPP, in which DPB ligands coordinated to two axial vertical dinuclear Zn₂(COO)₄. Both activated MOFs exhibited permanent porosity with high BET areas (1324 m² g^-1 for 1 and 1247 m² g^-1 for 2) and possessed narrow pore size distributions (0.93 nm for 1 and 1.02 nm for 2). Moreover, the adsorption behaviors of the two activated MOFs for CO₂ and light hydrocarbons (C1, C2, and C3) at low pressure were evaluated and favorable selectivity was proven for C₃H₈/C₃H₆ over CH₄. These two MOF materials reported in this study for selective CO₂ and light hydrocarbon capture have immense potential applications for environmental protection.