Modified Silica Adsorbents for Toluene Adsorption under Dry and Humid Conditions: Impacts of Pore Size and Surface Chemistry.

The pore surface structure and chemistry of the ordered mesoporous silica adsorbent (KIT-6) were modified for toluene removal, including the substituent groups on the silica surface and the pore size uniformity. Uniform pore size was obtained by low-temperature heat treatment of the template at 200 °C. In the dynamic adsorption process, better channel uniformity led to higher adsorption capacity under no humidity condition because of faster pore diffusion. However, better channel uniformity resulted in poor hydrophobicity under high humidity condition because it favors the adsorption of water vapor to a greater extent. The result of Biot number indicated that triphenyl-grafted KIT-6 had a faster intraparticle mass transfer rate than pure KIT-6. Triphenyl-grafted KIT-6 had a higher adsorption capacity for toluene as compared to phenyl-grafted KIT-6 under no humidity condition because of its higher surface area ( SA). The higher SA was owing to the low modification of phenyl, which was caused by the isolated grafting of silicon triphenyl rather than a more even coverage by silicon phenyl. As a result, triphenyl-grafted KIT-6 exposed more hydrophilic Si-O-Si groups and therefore was less hydrophobic than phenyl-grafted KIT-6.