Nitrogen-doped microporous carbon material decorated with metal nanoparticles derived from solid Zn/Co zeolitic imidazolate framework with high selectivity for CO2 separation

Abstract

To enhance CO2 separation selectivity and adsorption capacity for CCS applications, a core-shell Zn/Co zeolitic imidazolate framework (ZIF) synthesized through solvent-thermal reactions at 120 ℃ was pyrolyzed at different temperatures (ranging from 600 to 725 ℃) to obtain nanoporous carbon (NPC) materials with increased metal-N2 active sites and enhanced moisture stability. The NPC sample pyrolyzed (at 725 ℃) showed the highest CO2 uptake (3.22 mmol/g at 273 K and 1 bar), which was 2.13 times higher than that of the raw core-shell Zn/Co ZIF. In addition, it also exhibited the highest heat of adsorption towards CO2 (40 kJ/mol) and superior moisture stability compared to the other samples. Ideal adsorbed solution theory (IAST) calculations showed that this sample also possessed the highest CO2 separation selectivities of 24.3 and 40.2 for model biogas (CO2/CH4, volume ratio = 40:60) and coal-fired flue gas (CO2/N2, volume ratio = 15:85) mixtures, respectively, which were much higher than the corresponding values (2.11 and 3.71) for the raw core-shell Zn/Co ZIF. Through a combination of XPS, FTIR, PXRD, N2 adsorption-desorption, SEM, and TEM experimental techniques, it was demonstrated that the unsaturated metal sites (Me-N2) and pyridinic nitrogen groups were dominant active sites for CO2 adsorption via strong electrostatic interactions. The results obtained herein demonstrate that nitrogen-doped NPCs derived from core-shell Zn/Co ZIF are promising solid CO2 separation materials for industrial power plant flue gas and biogas purification applications.