Construction of a bifunctional Zn(ii)-organic framework containing a basic amine functionality for selective capture and room temperature fixation of CO2

Abstract

Selective carbon capture and utilization (CCU) as a C1 feedstock for the synthesis of value-added chemicals under ambient conditions catalyzed by porous MOFs constitutes one of the most promising solutions to mitigate the growing CO2 concentration in the atmosphere. Consequently, the synthesis of a novel 3D, microporous, bifunctional Zn(II)–organic framework, {[Zn2(TDC)2(DATRZ)]·(3H2O)·(DMF)}n (Zn-DAT) (where TDC = 2,5-thiophene dicarboxylate ion and DATRZ = 3,5-diamino-1,2,4-triazole), was achieved using a mixed ligand strategy. Single crystal X-ray structural analysis of the MOF revealed the presence of a 3D microporous structure with two types of 1D channels of dimensions 12.5 × 8.7 Å2 and 7.0 × 4.8 Å2 along the crystallographic c- and b-axes, respectively. The presence of basic –NH2 functionalized pores in Zn-DAT induces a selective adsorption property of CO2 with a high heat of adsorption (Qst) value of 39.5 kJ mol−1 which is supported by a theoretically computed binding energy (BE) of 40.9 kJ mol−1 . Interestingly, the Qst value observed for Zn-DAT is about 8 kJ mol−1 higher than that of the analogous MOF {[Zn2(TDC)(TRZ)2]·(DMA)·(MeOH)}n (Zn-TAZ) containing the 1,2,4-triazole (TAZ) linker, which highlights the critical role of –NH2 groups in enhancing the interaction energy for CO2. The significantly high value of Qst can be attributed to the stronger interaction of the acidic CO2 molecule with the basic –NH2 groups present in the 1D channels of the Zn-DAT MOF. Furthermore, the presence of both Lewis acidic Zn2+ ions and basic –NH2 groups resulted in the Zn-DAT MOF as an efficient heterogeneous catalyst for chemical fixation of CO2 into cyclic carbonates under mild conditions at RT. Herein, we report a rare example of porous MOFs for the capture and utilization of CO2 at RT and the influence of basic –NH2 groups on the high value of Qst and catalytic conversion of carbon dioxide.