Ethylenediamine-entrapped defective UiO-66(Zr) frameworks for improved CO2 adsorption and selectivity

Abstract

In this work, ethylenediamine was entrapped to defected UiO-66(Zr) frameworks to harvest defective amine@UiO-66(Zr) adsorbent (ED@DUiO) that showed improved CO2 performance and good renewability owing to a synergetic effect of creating defects and introducing amine molecules. The UiO-66(Zr) framework was in-situ modified using an acetic acid modulator, followed by grafting of ethylenediamine into the defected UiO-66(Zr) in n-hexane media. Results indicated that the defected UiO-66(Zr) framework had enhanced porosity and exposed more coordinatively unsaturated sites of Zr4+, favouring grafting amine molecules. Gas adsorption experiments revealed that ED@UiO exhibited significantly enhanced CO2 performance compared to the pristine MOF. At 25 °C and 100 kPa, the optimized ED@DUiO entrapped with ∼ 38.3 wt% amines exhibited a CO2-absorbing amount of ∼ 3.48 mmol/g, and IAST-CO2/CO and CO2/N2 selectivity of ∼ 46 and ∼ 78, respectively. Furthermore, the defected UiO-66 entrapped with ethylenediamine exhibited good separation of CO2 in the mixture with CO or N2 under dynamic flow adsorption conditions. The study provides a new strategy combining engineering defects and grafting alkylamine within MOF, which is a promising strategy for developing CO2-selective adsorbent materials.