Oxalamide-Functionalized Metal Organic Frameworks for CO2 Adsorption

Metal-organic frameworks (MOFs) have received great attention in recent years as potential adsorbents for CO₂ capture due to their unique properties. However, the high cost and their tedious synthesis procedures impede their industrial application. A series of new CO₂-philic oxalamide-functionalized MOFs have been solvothermally synthesized: {[Zn₃(μ₈-OATA)_1.5(H₂O)₂(DMF)]·5/2H₂O·5DMF}_n (Zn-OATA), {[NH₂(CH₃)₂][Cd(μ₄-HOATA)]·H₂O·DMF}_n (Cd-OATA), and {[Co₂(μ₇-OATA)(H₂O)(DMF)₂]·2H₂O·3DMF}_n (Co-OATA) (H₄OATA = N,N'-bis(3,5-dicarboxyphenyl)oxalamide). In Zn-OATA, the [Zn₂(CO₂)₄] SBUs are connected by OATA^4- ligands into a 3D framework with 4-connected NbO topology. In Cd-OATA, two anionic frameworks with a dia topology interpenetrated each other to form a porous structure. In Co-OATA, [Co₂(CO₂)₄] units are linked by four OATA^4- to form a 3D framework with binodal 4,4-connected 4²·8⁴ PtS-type topology. Very interestingly, Cu-OATA can be prepared from Zn-OATA by a facile metal ions exchange procedure without damaging the structure while the CO₂ adsorption ability can be largely enhanced when Zn(II) metal ions are exchanged to Cu(II). These new MOFs possess channels decorated by the CO₂-philic oxalamide groups and accessible open metal sites, suitable for highly selective CO₂ adsorption. Cu-OATA exhibits a significant CO₂ adsorption capacity of 25.35 wt % (138.85 cm³/g) at 273 K and 9.84 wt % (50.08 cm³/g) at 298 K under 1 bar with isosteric heat of adsorption (Q_st) of about 25 kJ/mol. Cu-OATA presents a very high selectivity of 5.5 for CO₂/CH₄ and 43.8 for CO₂/N₂ separation at 0.1 bar, 298 K. Cd-OATA exhibits a CO₂ sorption isotherm with hysteresis that can be originated from structural rearrangements. Cd-OATA adsorbs CO₂ up to 11.90 wt % (60.58 cm³/g) at 273 K and 2.26 wt % (11.40 cm³/g) at 298 K under 1 bar. Moreover, these new MOFs exhibit high stability in various organic solvents, water, and acidic or basic media. The present work opens a new opportunity in the development of improved and cost-effective MOF adsorbents for highly efficient CO₂ capture.

Cobalt-Based Metal-Organic Frameworks for Adsorption of CO2 and C2 Hydrocarbons: Effect of Auxiliary Ligands with Different Functional Groups

Recently, metal-organic frameworks (MOFs) have been investigated as potential materials for CO₂ capture and light hydrocarbon storage/separation due to their high porosity, large surface area, and tunable skeleton structures. In this work, the six cobalt-based MOFs 1-6 were successfully synthesized under solvothermal conditions by a mixed-ligand strategy. 1 and 2 have the same framework structure with a topology of {4²·5}₂{4⁴·5¹⁰·6⁷·7⁶·8}, while the structures of the 3-6 frameworks are the same with a topology of {4²·5}₂{4⁴·5¹⁰·6⁹·7⁴·8}. The adsorption properties of these MOFs for CO₂ and C₂ hydrocarbons were then investigated, and the effect of the functional groups was discussed. The results revealed that the introduction of amino and bromo groups could effectively strengthen the adsorption performance.

Sonochemical synthesis and characterization of four nanostructural nickel coordination polymers and photocatalytic degradation of methylene blue

Four nanostructural nickel(II) coordination polymers {[Ni(ttpa)(1,4-ndc)(H₂O)₂]·2H₂O}_n (1), {[Ni(ttpa)(1,3-bda)]·2H₂O·DMF}_n (2·2H₂O·DMF), {[Ni(ttpa)(1,4-bdc)]·H₂O}_n (3) and {[Ni(ttpa)(aip)(H₂O)]·3H₂O}_n (4·3H₂O) were synthesized using hydrothermal and sonochemical methods (ttpa = tris(4-(1,2,4-triazol-1-yl)phenyl)amine, 1,4-ndc = 1,4-naphthalenedicarboxylate, 1,3-bda = 1,3-benzenediacetate, 1,4-bdc = 1,4-benzenedicarboxylate, aip = 5-aminoisophthalate), and characterized by elemental analysis, IR spectra, scanning electron microscopy, single-crystal and powder X-ray diffraction analysis, optical band gaps, VB XPS spectra and luminescence. The effects of sonication power, time and frequency on the size and morphology of nano-sized 1-4 have been studied. 1 exhibits an unusual 2D + 2D → 3D inclined polycatenated motif based on the (3,3)-coordinated 6³-hcb topology. 2 shows a (3,4)-coordinated 2D network of the bey topology. 3 presents a rare example of the 4-fold interpenetrating array of (3,5)-coordinated 3D network belonging to the 35T1 topology type. 4 displays an unusual 2D → 3D polythreaded network based on 2D sql networks. 1-4 exhibit luminescent emissions at 409, 399, 413 and 402 nm, respectively. 1-4 are semiconducting in nature, with E_g of 2.12 eV (1), 2.34 eV (2), 2.32 eV (3), and 2.47 eV (4). 1-4 are good catalysts for the degradation of MB under visible light irradiation. The effects of the size and morphology of nano-sized 1-4 on the photocatalytic efficiencies were studied. The higher sonication frequency obtains uniform and smaller nano-sized coordination polymers which have higher catalytic efficiencies.

Synthesis, structure and adsorption properties of lanthanide-organic frameworks with pyridine-3,5-bis(phenyl-4-carboxylate)

Under solvothermal conditions, reactions of pyridine-3,5-bis(phenyl-4-carboxylic acid) (H2L) with lanthanide metal salts give rise to three new metal-organic frameworks (MOFs) with the formula {[Ln4(L)3(μ3-OH)4(H2O)4]·(NO3)2·solvent}n [Ln = Er (1), Yb (2) and Lu (3)]. The complexes were characterized by single crystal and powder X-ray diffraction, IR and thermogravimetric analyses. They have the same two-fold interpenetrating three-dimensional (3D) framework structures with [Ln4(COO)6(μ3-OH)4(H2O)4] clusters as secondary building units (SBUs) and a rare 6-connected lcy topology with the point (Schläfli) symbol of {3(3)·5(9)·6(3)}. Interestingly, 1-3 show selective and hysteretic sorption of CO2 over N2, and the photoluminescence properties of the complexes were also investigated.