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

• Pore size distribution tuning of MOFs for optimal selective performance was achieved by implementing a core-shell strategy. • A size exclusion mechanism for effective selective separation of H 2 S and CO 2 from gas streams was successfully validated. • High H 2 S and CO 2 uptake capacity on core-shell MU nanocrystals can be seen, comparable and/or higher than literature data. • Core-shell MU nanocrystals possessed higher H 2 S/CH 4 , H 2 S/N 2 , CO 2 /CH 4 and CO 2 /N 2 selectivity than pristine MIL-101(Cr). • The core-shell MU nanocrystals showed outstanding recyclability for long-term cyclic operations. Removal of H 2 S and CO 2 is essential in diverse industrial applications such as natural gas treatment for avoiding their corrosion, toxicity, and environmental damages. To improve selective separation of H 2 S and CO 2 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 H 2 S, CO 2 , CH 4 , and N 2 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 H 2 S (20.62 mmol g -1 at 15 bar) and CO 2 (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 H 2 S/CH 4 , H 2 S/N 2 , CO 2 /CH 4 , and CO 2 /N 2 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 H 2 S and CO 2 capture and separation.