A stable metal-organic framework with suitable pore sizes and rich uncoordinated nitrogen atoms on the internal surface of micropores for highly efficient CO2 capture

An air-stable tetrazolate-containing framework, [ZN(2)L(2)]center dot 2DMF (NENU-520, H2L = 4-(1H-tetrazole-5-yl) biphenyl-4-carboxylic acid), with uncoordinated N atoms on its internal surface was solvothermally synthesized and structurally characterized. This metal-organic framework (MOF) exhibited high CO2 uptake of 79.9 cm(3) cm(-3) at 298 K and 100 kPa, as well as excellent adsorption selectivity for CO2 over CH4 and N-2. Particularly, its exceptionally high selectivity of CO2 over N-2 at 298 K has ranked NENU-520 among the highest MOFs for selective CO2 separation. Furthermore, the potential application of NENU-520 for the fixed bed pressure swing adsorption (PSA) separation of CO2 from CH4 and N-2 has been validated via simulated breakthrough experiments. The small channel with the size of 3.6 angstrom, combined with CO2-accessible free nitrogen atoms directed toward the inner surface, is believed to contribute to its high CO2 uptake capacity and selectivity. Thus, this work represents a unique way to target MOF materials for highly selective CO2 separation by incorporating CO2-philic functional sites on pore surfaces, and at the same time optimizing pore sizes.