Effects of -NO2 and -NH2 functional groups in mixed-linker Zr-based MOFs on gas adsorption of CO2 and CH4

This study was undertaken to evaluate the effects of mixing BDC-NO2 and BDC-NH2 linkers in the synthesis of Zr-based metal organic frameworks (Zr-MOFs) on their adsorption and separation of CO2 and CH4. UiO-66 with single or binary -NO2 and -NH2 samples were synthesized under solvothermal conditions and activated by solvent exchanging using methanol. Structural analyses of the materials were conducted using FTIR, XRD, TGA, SEM, (HNMR)-H-1 and N-2 adsorption/desorption techniques and adsorption of CO2 and CH4 at high pressures and different temperatures (273 and 298 K) was investigated. It was found that UiO-66-NH2 exhibited higher CO2 and CH4 adsorption capacities than those of UiO-66-NO2. Addition of -NH2 functional group in UiO-66-NO2 could enhance CO2 and CH4 adsorption due to the extra CO2 adsorption sites of -NH2 functional groups. Addition of -NO2 functional group to UiO-66-NH2 at a low loading could also increase CO2 and CH4 adsorption, however, a high loading of NO2 functional group to UiO-66-NH2 would result in decreased adsorption.