Influence of humidity on the removal of volatile organic compounds using solid surfaces

In recent years, much attention has been devoted to understand how the humidity affects the volatile organic compound (VOC) removal efficiencies using absorbents, photocatalysts or dark-catalysts and both positive and negative effects of humidity on VOC removal have been reported. We show that sorption capability of VOCs of absorbents with high surface areas can be significantly reduced by the competitive adsorption with water in the air and, by hydrophobically modifying the absorbent surfaces, selective sorption of VOCs to water molecules is achieved. For the TiO₂ photocatalysts, humidity was found to have both positive and negative effects on catalytic activity; humidity facilitates the total oxidation of toluene to CO₂ allowing the long-term stability of the catalytic activity, on the other hand, reduces the adsorption of VOCs on the catalyst surface. By depositing TiO₂ islands on hydrophilic nanodiamond nanoparticles, positive effect of humidity becomes more pronounced. Positive and negative effects of humidity analogous to those on photocatalyst were also observed for the dark-catalysts, NiO nanoparticle decorated mesoporous silica. TiO₂ interlayer with a high affinity toward toluene was applied between SiO₂ and NiO and, as a result, negative effect of humidity, reduction of toluene adsorption in the presence on water, is suppressed.