New Insights into the Capture of Low-level Gaseous Pollutants in Indoor Environment by Carbonaceous Materials: Effects of Functional Groups, Pore Size, and Presence of Moist

Abstract

Abating the common indoor pollutants by adsorption is profoundly governed by the properties of adsorbent and the presence of water. We carried out Monte Carlo simulations of adsorption of five common indoor pollutants (benzene, hydrogen sulfide, sulfur dioxide, formaldehyde and ammonia) on functionalized graphitic pores at 298 K with and without the presence of water to investigate the effects of concentration and type of functional groups (FGs) and pore size. The simulation results for the isotherm, the isosteric heat at zero loading, and the spatial distribution of water and pollutant were analyzed to evaluate the effectiveness of remediation of these pollutants. It is found that adsorption of the pollutants at typical indoor concentrations (sub-ppm) occurs in the Henry's law region where the interaction between pollutant and adsorbent dominates the intermolecular interaction of pollutant. Regardless of the pollutants water is always strongly attracted to the FGs in forms of clusters, and the abatement of the pollutant rests on its electrostatic interactions with water molecules in the clusters and van der Waals interactions with the graphitic surface. The relative interplay of these interactions depends on the properties of the pollutant, and this gives rise to two distinct phenomena: competition and cooperation. For ammonia and formaldehyde whose electrostatic interactions with water (in the cluster on the FGs) are strong, their capture is enhanced. On the other hand, the abatement of benzene and hydrogen sulfide is negatively affected because of their weaker interactions with water. Given the inevitable occupation over the FGs by water, more attention should be paid on the interactions between adsorbed water and the pollutants.