Metal-organic frameworks composed of nitro groups: Preparation and applications in adsorption and catalysis

In this review, metal–organic frameworks functionalized with nitro groups (MOF-NO₂s) were analyzed, for the first time, in terms of their preparation and applications. MOF-NO₂s were obtained by direct synthesis from nitro-functionalized linker precursors and by post-synthetic modification of a pristine MOF without a –NO₂ group. Additionally, the applications of MOF-NO₂s, specifically in adsorption and catalysis, were discussed. CO₂ capture using MOF-NO₂s was highly effective due to the polar nitro group which aided in quadrupole–dipole interactions. Furthermore, on account of the electron-withdrawing nitro group, MOF-NO₂s were efficient in the adsorption of other gases, such as nitrogen. Similarly, MOF-NO₂s were promising for the removal of hazardous organics from water and particulate matter from the air mainly due to the charge separation on the nitro group. MOF-NO₂s could be very useful in catalysis that relies on the Lewis acidity because the electron-withdrawing nitro group can increase Lewis acidity. MOF-NO₂s can be used in other applications, such as detection of H₂S. Based on the analysis of the achievements thus far, the prospects of MOF-NO₂s for further research were provided.