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 Ų and 7.0 × 4.8 Ų 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 (Q_st) 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 Q_st 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 Q_st 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 Q_st and catalytic conversion of carbon dioxide.