Enhanced CO2 adsorption and selectivity over N2 and CH4 in UiO-67 modified by loading CuO NPs through solvent exchange

Abstract

There is an urgent need for new CO₂ adsorbents to overcome the rapidly increasing CO₂ pollution. New CuO@UiO-67 composites were prepared by encapsulating CuO nanoparticles (NPs) in the shallow pore channels of UiO-67 through postsynthetic exchange (PSE) to form a core–shell structure. The composites were characterized via TEM, XRD, and BET analyses, and single component adsorption isotherm measurements of CO₂, CH₄ and N₂ were performed at different temperatures. The selectivities of CO₂/CH₄ and CO₂/N₂ and the isosteric heats of CO₂ adsorption were estimated based on the ideal adsorption solution theory (IAST) and the Clausius–Clapeyron equation, respectively. The highest CO₂ uptake of CuO@UiO-67 was achieved at 273 K and 100 kPa with 61.9 cc g⁻¹, which was twice that of parent UiO-67. The significant increase in CO₂ uptake was not only due to the introduction of CuO NPs in the pore channel of CuO@UiO-67, but also due to the new open nitrogen sites due to ligand substitution. The adsorption selectivities of CO₂/CH₄ and CO₂/N₂ at 298 K and 100 kPa were 9.2 and 54.3, respectively. Furthermore, CuO@UiO-67 could efficiently separate the CO₂/N₂ mixture under a dynamic flow condition. These excellent properties suggest that the CuO@UiO-67 composite is a promising and efficient CO₂ adsorbent material. This study lays a solid foundation for metal oxide-modified MOFs and is a great contribution to the preparation of new adsorbents.