Significant promotion of NO separation selectivity from flue gas by the –NH2 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. The bimetallic metal–organic frameworks 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. FeNi-BDC-NH2 demonstrated superior NO adsorption performance and high adsorption selectivity, indicating that the introduction of NH2 on the ligand can improve the adsorption capacity and selectivity of the material for NO, which also provides a new strategy for adsorption and separation of NO in a flue gas environment. (Image credit: Li Hao.) [ABSTRACT FROM AUTHOR]