Ambient temperature NO₂ removal by reversible NO₂ adsorption on copper-based metal-organic frameworks (MOFs)-derived nanoporous adsorbents

Nitrogen dioxide (NO₂) is a potent atmospheric pollutant generated from fossil fuel combustion at power plants, industrial plants, and vehicles, which raises serious health concerns (e.g., respiratory diseases) and contributes to severe environmental pollution issues (e.g., acid rain and ground-level ozone). Adsorption is an efficient approach for ambient temperature NO₂ removal, whose efficiency highly depends on the design of the adsorbents. The widely reported activated carbon adsorbents suffer from low and typically irreversible NO₂ capacity apart from co-generation of considerable amounts of polluting NO (up to 50% of adsorbed NO₂), which is released back into the atmosphere. Herein we report copper-based metal–organic framework (MOF)-derived carbon materials (i.e., Cu@C(CuBTC) and Cu@C(CuBDC)) featuring high NO₂ capacity coupled with minimal release of NO and outstanding reusability for NO₂ removal under ambient temperature. Both Cu@C(CuBTC) and Cu@C(CuBDC) showed an impressive improvement (up to 13.5 times) in NO₂ capacity over their pristine MOFs counterparts, with Cu@C(CuBTC) showing the highest NO₂ capacity (4.97 mmol/g) and minimal (<20 % of adsorbed NO₂) release of NO in this study. Such a massive improvement in the NO₂ capacity of carbonized composites is attributed to highly active and homogenously dispersed Cu nanoclusters, which serve as adsorption sites and play the dominant role in NO₂ removal. Further, for the first time, Cu@C(CuBTC) exhibited outstanding reusability for NO₂ removal under humid conditions, reflected by stable NO₂ capacity in the cyclic adsorption tests (5 cycles), suggesting a great potential for real-world applications. This study provides a general and facile strategy for designing highly dispersed, water-resistant, and stable copper nanoclusters on carbon support for efficient adsorptive removal of various toxic gases under ambient temperature.