pH-Induced Two Co (II) Metal–Organic Frameworks with Different Topologies: Magnetism and CO<sub>2</sub>/CH<sub>4</sub> Separation
Yujuan Zhang, Yujuan Zhang, Yaqing Zhang, Yaqing Zhang, Xiutang Zhang, Tuoping Hu
Abstract
The self-assembly process of the metal–organic framework (MOF) is affected by many factors, so the construction of the MOF with unique structure and properties is still a great challenge. Herein, based on 3,5-bis (2,5-dicarboxylic phenyl) benzoic acid (H 5 L), two novel 3D porous Co-MOFs, {[Co 3 (HL) 2 (μ 2 -H 2 O) 2 ]·2NH 3 ·4CH 3 CN·4H 2 O} n (Co-MOF 1 ) and {[Co 2.75 (L)(H 2 O) 3.5 (μ 3 -OH)]·0.5NH 3 ·3CH 3 CN·3H 2 O} n (Co-MOF 2 ), were designed and constructed by changing the pH under solvothermal condition. Co-MOF 1 displays a 2-node (4, 8)-c flu topological network with the symbol of {4· 12 6· 12 8 4 }{4 6 } 2, while Co-MOF 2 exhibits a 3-n (4,4,6)-c 4,4,6T17 (MOF.ttd) topology type with the symbol of {4· 2 8 4 }{4· 4 6 2 } 4 {4· 7 6· 8 8 2 } 2 . Meanwhile, the magnetic test results of Co-MOFs show that Co-MOFs have antiferromagnetic interaction between Co (II) ions. Furthermore, the adsorption selectivities ( S ads ) of Co-MOFs for 0.05/0.95 CO 2 /CH 4 binary mixture are 27.1 (Co-MOF 1 ) and 38.0 (Co-MOF 2 ) at 298 K, respectively, and the high adsorption performance of Co-MOFs for CO 2 was attributed to the smaller dynamic radius, larger quadrupole moment, and higher polarizability of CO 2, the strong adsorption heat of Co-MOFs for CO 2, and the strong interaction force between Co-MOFs and CO 2 . In addition, the action sites and bond energy of the hydrogen bonds between CO 2 and Co-MOF 2 (O–H···O) are obviously better than those between CO 2 and Co-MOF 1 (C–H···O) simulated by Grand canonical Monte Carlo simulations.