Transition-Metal-Containing Porphyrin Metal–Organic Frameworks as π-Backbonding Adsorbents for NO₂ Removal

Mitigating ambient nitrogen dioxide (NO₂) pollution via selective adsorption on porous materials is a promising approach to tackle such an increasingly pressing environmental health issue. However, very few porous adsorbents have sufficiently high NO₂ adsorption capacity and good regenerability simultaneously. Here we attempt to address this challenge by developing π-backbonding adsorbents in the transition metal (TM) incorporated porphyrin metal–organic frameworks (PMOFs). Breakthrough experiments show that PMOFs with inserted TMs achieve appreciable NO₂ capacity and good regenerability. Combined in situ DRIFTS, synchrotron powder XRD, and DFT calculations reveal the adsorption mechanism: NO₂ partially transforms to N₂O₄ and interacts with transition metal via π-backbonding and Al-node via hydrogen bonding. This work affords new insights for designing next-generation adsorbents for ambient NO₂ removal and presents PMOFs as a platform to tailor π-backbonding adsorbents.