Fabrication and application of novel core–shell MIL-101(Cr)@UiO-66(Zr) nanocrystals for highly selective separation of H2S and CO2

Abstract

Removal of H2S and CO2 is essential in diverse industrial applications such as natural gas treatment for avoiding their corrosion, toxicity, and environmental damages. To improve selective separation of H2S and CO2 at ambient temperature, we designed novel core–shell-structure MOFs based on a porous MIL-101(Cr) as seeds and a less porous UiO-66(Zr) shell. MU-4 and MU-8 nanocrystals, with different shell growth times, were synthesized and characterized by different techniques. The adsorption isotherms of H2S, CO2, CH4, and N2 on individual and hybrid samples were measured, using a volumetric method in a wide pressure region and at different temperatures. MU nanocrystals exhibited high adsorption capacity for both H2S (20.62 mmol g−1 at 15 bar) and CO2 (17.21 mmol g−1 at 35 bar), elevated up to 84.4 % and 121.8 % compared to pristine UiO-66(Zr). Most importantly, ideal adsorbed solution theory (IAST) showed that adsorption selectivity of H2S/CH4, H2S/N2, CO2/CH4, and CO2/N2 was significantly improved up to 7.8 %, 47.0 %, 32.1 % and 59.9 % at highest pressure compared to pristine MIL-101(Cr). Besides additional open metal sites, this high separation efficiency was ascribed to the size exclusion separation due to optimized pores diameter of MU nanocrystals. According to impressive preferential gas adsorption along with excellent cyclic adsorption–desorption performance and thermal stability, MU nanocrystals can broaden the horizon of H2S and CO2 capture and separation.