Transition-Metal-Containing Porphyrin Metal-Organic Frameworks as pi-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 pi-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 pi-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 pi-backbonding adsorbents