Significant promotion of NO separation selectivity from flue gas by the –NH 2 functional group on Fe–Ni bimetallic MOF at ambient conditions

In this paper, the bimetallic metal–organic frameworks (MOFs) of FeNi-BDC and FeNi-BDC-NH₂ (BDC, 1,4-benzenedicarboxylate) with similar Fe/Ni molar ratio, crystal structure, porosity and thermal stability were synthesized by a solvothermal method. The results of adsorption experiments at ambient conditions showed that the adsorptive uptake of NO, CO₂, O₂ and N₂ on FeNi-BDC were all very small under different adsorption partial pressures, with FeNi-BDC displaying a weak adsorption property because of its lack of unsaturated adsorption sites. On the contrary, at 100 kPa, the adsorption of NO by FeNi-BDC-NH₂ was considerably higher than that by FeNi-BDC, indicating that the incorporation of NH₂ on the ligand could effectively enhance the adsorption of NO. The adsorption capacity of FeNi-BDC-NH₂ for NO reached 142.17 cm³ g⁻¹, which was considerably higher than its capacity for CO₂, O₂ and N₂ under the same conditions. Ideal Adsorption Solution Theory simulations calculated the adsorption selectivity for NO/CO₂ and NO/O₂ under a mixed atmosphere to reach 1325 and 13,346 respectively, demonstrating high adsorption selectivity. Through in situ infrared experiments and calculations of the enthalpy of adsorption, it was demonstrated that FeNi-BDC-NH₂ adsorbed NO because NO can combine with NH₂ in the material to form a NONOate structure. A preliminarily exploration of the mechanism of NO adsorption and the influence of NH₂ functional groups on the adsorption and separation of NO revealed that the selectivity of adsorption was closely related to the variability of the enthalpy of adsorption. This also provided a new strategy for the adsorption and separation of NO in the flue gas environment.