Zero-emission NO2 capture using divalent metal cation-exchanged zeolites for air purification

The global adoption of hydrogen and biofuels, though central to decarbonization, risks aggravating NO₂ pollution as their combustion drives up NOx emissions through hotter flames and excess oxygen. Effective ambient NO₂ removal is critical for protecting human health, yet existing adsorbents often release toxic NO, limiting practical deployment. Here, we overcome this grand challenge by developing divalent metal cation-exchanged zeolites that achieve complete NO₂ capture with "zero" NO emission. Exemplified by Ca²⁺- and Mn²⁺-exchanged zeolites, these materials operate under both dry and humid (70% RH) conditions, even at NO₂ concentrations up to 500 ppm. Mechanistic studies reveal that divalent cations, acting as surface active sites, can suppress NO formation via stabilizing its intermediate. We further demonstrate real-world applicability by integrating these zeolites into a wearable air-purifying respirator, enabling a "zero-NOx shield" for personal protection. This work establishes NO₂ adsorption chemistry and offers a scalable pathway to clean air solutions.