Synergistic Nitrogen Binding Sites in a Metal-Organic Framework for Efficient N2/O2 Separation

Porous materials with d(3) electronic configuration open metal sites have been proved to be effective adsorbents for N-2 capture and N-2/O-2 separation. However, the reported materials remain challenging to address the trade-off between adsorption capacity and selectivity. Herein, we report a robust MOF, MIL-102Cr, that features two binding sites, can synergistically afford strong interactions for N-2 capture. The synergistic adsorption site exhibits a benchmark Q(st) of 45.0 kJ mol(-1) for N-2 among the Cr-based MOFs, a record-high volumetric N-2 uptake (31.38 cm(3) cm(-3)), and highest N-2/O-2 selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL-102Cr can efficiently capture N-2 from a 79/21 N-2/O-2 mixture, providing a record 99.99 % pure O-2 productivity of 0.75 mmol g(-1). In situ infrared spectroscopy and computational modelling studies revealed that a synergistic adsorption effect by open Cr(III) and fluorine sites was accountable for the strong interactions between the MOF and N-2.