NOx de-pollution by hardened concrete and the influence of activated charcoal additions

The atmospheric pollution by nitrogen oxides affects the health of millions of people located in urban areas. Our work demonstrates that, even in the absence of photocatalysts, concrete walls can strongly absorb NO2 and limit the intensity of pollution peaks. Our results show that concretes can continuously absorb a significant fraction of NO2 from the surrounding atmosphere over long periods, probably due to a reaction with strongly alkaline cement hydrates. Moreover, the introduction of a small amount of activated charcoal into the concrete mix can significantly enhance and prolong this NO2 absorption without greatly increasing total porosity or decreasing strength. We hypothesize that the NO2 is adsorbed irreversibly by a neutralization reaction with the alkaline aqueous solution covering the surfaces of the hydrates and the activated charcoal. Simple calculations suggest that walls made of activated charcoal concrete could ameliorate the problem of NO2 pollution peaks in road tunnels and parking garages.

► Even in the absence of photocatalysts, concrete can strongly absorb NO2.
► Concretes can absorb NO2 due to a reaction with alkaline cement hydrates.
► Introduction of activated charcoal in concrete enhances the NO2 absorption rate.
► A constant de-pollution was established for a minimum of 20 h of continual exposure.