Effects of carbon phase deposition in silica gel pores on NO2 reactive adsorption at ambient conditions on carbon/silica composites.

Silica-carbon composite samples containing various carbon contents deposited within a silica gel matrix were synthesized. The composites were evaluated as nitrogen dioxide adsorbents at ambient conditions in either wet (70% RH) or dry air streams. The surface chemistry and textural features of the initial and exposed samples were characterized using nitrogen adsorption, potentiometric titration, thermal analysis, and FT-IR. The deposition of the carbon phase significantly increased the amount of NO2 adsorbed in comparison with that adsorbed on the silica gel. With an increase in the amount of carbon an increase in the performance was found. The positive effect was especially noticed when water was present in the system. An oxidation of the surface and release of NO was observed. The acidification/oxidation of the surface is more pronounced in moist conditions, and it is linked to the formation of nitric acid adsorbed in the pore system. The carbon phase besides providing some level of hydrophobicity also brings phenolic groups to the system, on which immobilization of NO2 takes place via nitrification reactions.