Role of sulfur and nitrogen surface groups in adsorption of formaldehyde on nanoporous carbons

S-doped nanoporous carbon, and commercial activated carbons, as received or modified by an incorporation of sulfur and nitrogen functional groups to their surface, were tested as low concentration formaldehyde (1 ppmv) adsorbents. The breakthrough capacities, in dry and wet conditions, were measured. The surface properties of the samples were evaluated using nitrogen sorption, potentiometric titration, thermal analysis, and XPS. The incorporation sulfur and/or nitrogen functional groups led to an increase in the amount of HCHO removed from air. These group (pyridines, amines, thiophenes, sulfones) when located in large pores increase the utilization of the carbon surface for formaldehyde adsorption providing chemical reactivity. In this aspect, rich in sulfur carbon of a relatively low surface was found as the most efficient formaldehyde adsorbent. Its HCHO adsorption capacity was 7.15 × 10-4 mg m-2 whereas on melamine modified carbon of a high surface area 4.23 × 10-4 mg m-2 were adsorbed. On the microporous carbon of basic nature reactions of HCHO with phenols block this carbon porosity and thus excluded the adsorption centers in ultramicropores for physical adsorption decreasing the adsorption capacity. Water in the system decreases the HCHO capacity between 10 and 30%, owing to its competitive adsorption on polar centers.