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.