Porous Zn(Bmic)(AT) MOF with Abundant Amino Groups and Open Metal Sites for Efficient Capture and Transformation of CO₂

Abstract

An efficient Zn(Bmic)(AT) MOF with available Lewis acid-base blocks was prepared by a solvothermal method combining the mixed ligands 5-aminotetrazole (HAT) and 1-benzimidazole-5-carboxylic acid (H₂Bmic). The prepared Zn(Bmic)(AT) catalyst is rich in amino groups, uncoordinated oxygen atoms, and multiple open metal sites (OMSs), which contribute to CO₂ adsorption of 79 cm³/g at 273 K and 52 cm³/g at 298 K, with high adsorption enthalpy (28 kJ mol^-1). Furthermore, its multiple functional sites facilitate CO₂ cycloaddition to various small-molecule epoxides to give five-ring cyclic carbonates with the assistance of a Bu₄NBr cocatalyst, achieving a high TON of 170 for propylene carbonates (PC) under solvent-free, mild conditions (80 °C, 5 bar). In addition, the Zn(Bmic)(AT) catalyst exhibits good recyclability for six consecutive cycles. Moreover, a feasible synergistic mechanism of Zn(Bmic)(AT)/Bu₄NBr catalysts for CO₂ conversion into cyclic carbonate is proposed.