Nitrogen dioxide (NO₂) pollution causes serious environmental problems and poses substantial health threats to human beings. NO₂ leads to the formation of photochemical smog, acid rain, as well as some human diseases. Various NO₂ emission sources, such as exhaust from vehicles and flue gas from the burning of fossil fuels, contribute to the accumulation of NO₂ in the atmosphere. Although the state of the art selective catalytic reduction technology applicable to NO₂ conversion at high temperatures (250-600 ^oC) has been widely used in industry, the control and abatement of ambient NO₂ emission is still an elusive challenge. Dr. Jin Shang Group in School of Energy and Environment in collaboration with researchers from the Australian Synchrotron, Jilin University, and Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences develops an efficient technology for ambient NO₂ removal based on selective adsorption on porous materials and the results were published on a top General Chemistry journal – Angewandte Chemie International Edition (https://doi.org/10.1002/anie.202007054).

In this study we attempt to address this challenge by developing π-backbonding adsorbents in the transition metal incorporated porphyrin metal-organic frameworks (PMOFs). The idea is originated from nature – the ferroporphyrin in a natural molecule-hemoglobin shows strong affinity toward π molecules, such as oxygen and carbon monoxide, via a unique interaction called π-backbonding. The π-backbonding can be formed and tuned between transition metals and π molecules to realize selective binding, which can be used to enable selective gas adsorption. In other words, it allows for gas purification by selectively removing a certain gas component from a mixture gases stream, such as removing NO₂ from air. Since NO₂ is a π molecule, we designed PMOFs featuring a large density of transition metal sites to selectively bind NO₂ and thus remove it from air, achieving appreciable NO₂ capacity and good regenerability. Our work affords new insights for designing next-generation adsorbents for ambient NO₂ removal and presents PMOFs as a platform to tailor π-backbonding adsorbents for various gas separation applications pertaining to energy production and environmental remediation.