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

Abstract

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, ¹HNMR and N₂ 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.