Improved N2O capture performance of chromium terephthalate MIL-101 via substituent engineering

The capture of N 2 O from CO 2 by an adsorption-based mechanism remains a significant challenge due to their similar molecular sizes and physical properties. Although substituent engineering has been widely employed for the selectivity regulation and improvement of gas mixtures in metal-organic frameworks, its effect on N 2 O/CO 2 separation has yet not been explored. Herein, four isoreticular MTN-type metal-organic frameworks (MOFs) with different substituents (-H, –NH 2 , -Br or –NO 2 ) are reported for the capture of N 2 O from a N 2 O/CO 2 mixture. As revealed by isothermal measurements, thermodynamic studies and ideal adsorbed solution theory computations, the N 2 O/CO 2 separation potential can be effectively improved by an electron-donating group (-NH 2 ), whereas electron-withdrawing groups (-NO 2 or -Br) exhibit the opposite effect. Notably, MIL-101(Cr)–NH 2 exhibits, by far, the highest ideal adsorbed solution theory equilibrium adsorption selectivity of 1.91 for 50/50 N 2 O/CO 2 . The N 2 O/N 2 separation ability of the modified materials is also studied and functionalization with a -Br group yields an improved separation potential compared to the parent MIL-101(Cr) material. The strategy of using substituents to enhance the N 2 O/CO 2 separation efficiency of MOFs could also be extended to other porous materials for chemical separation processes.