Designing multivariate porphyrin-based metal-organic frameworks with Ni/Co dual-metal atom sites for cooperative NO₂ capture and NO retention

Selective adsorption using porous materials is a promising approach to removing ambient nitrogen dioxide (NO₂). However, the highly reactive nature of NO₂ and the often-associated release of nitric oxide (NO) render a formidable challenge in developing effective and stable adsorbents. Here, we designed multivariate porphyrin-based metal–organic frameworks (MTV-PMOFs Al-PMOF(Ni_xCo_y)) featuring atomically dispersed Ni/Co dual-metal centers in the porphyrin ring as active adsorption sites, as robust adsorbents capable of synergistically boosting NO₂ adsorption capability and retaining the evolved NO. The introduction of the Ni/Co dual-metal sites in MTV-PMOFs greatly enhanced the NO_x adsorption performance. Under dry conditions, Al-PMOF(Ni₁Co₁) exhibited a NO₂ adsorption capacity of 3.66 mmol/g (100 ppm NO₂ in feed), among the highest under similar conditions, a high NO retention ability, and good regenrability (85%). Under wet conditions, its NO₂ removal capacity was further elevated by more than 50% (5.65 mmol/g). Moreover, the Ni/Co ratio in MTV-PMOFs dictates a structure–property relationship between the released amount of NO and adsorbed capacity of NO₂. Such a corporative NO₂ and NO adsorption was for the first time established in MOFs. The material stability and potential economic value were also investigated to demonstrate the applicability of MTV-PMOFs as NO₂ adsorbents. This work provides new perspectives for the development of adsorption-based technology for mitigating ambient NO₂ pollution and managing other corrosive and toxic gases.