Enhancing CO2 adsorption capacity and selectivity of UiO-67 through external ligand modification

Abstract

To address the escalating issue of CO2 pollution, the development of innovative CO2 adsorbents has been necessitated, leading to the exploration of UiO-67-based materials. In this study, UiO-67 was synthesized with meticulous selection of the appropriate modulators in optimal ratios. Subsequently, 4-iodopyrazole, a ligand distinguished by its local electric fields and polar sites, was incorporated to fabricate UiO-67-I. This novel material underwent examination employing techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) analysis. The adsorption rates of gases including CO2, CH4, and N2 were measured at various temperatures. Utilizing the ideal adsorbed solution theory (IAST) and the Clausius-Clapeyron equation, the selectivity of CO2 against CH4 and N2 was calculated, along with the CO2 adsorption isotherms. Remarkably, UiO-67-I(50) demonstrated a CO2 adsorption capacity of 1.84 mmol/g at 298 K and 1 bar, representing a significant enhancement attributable to the ligand's enhanced local electric fields and polar sites. The selectivities for CO2 over CH4 and CO2 over N2 were determined to be 14.2 and 84.6, respectively, under these conditions. Moreover, UiO-67-I(50) proved effective in the separation of CO2 from N2 under dynamic flow conditions, showcasing its potential for practical application in gas separation.