Short-term sorption of toluene vapor onto natural organic materials

The effects of surface area, micro-porosity, and surface chemical structure on the sorption of toluene vapor onto three model natural organic materials (NOMs), including two peats (CH and HS) and one tree bark compost (TB) were examined. The BET surface area, pore size distribution, element composition, sorption kinetics and isotherms, and carbon functionality (CP/MAS ¹³C-NMR spectra) were measured for the model organic matters. All the three NOMs have small BET-surface areas (below 5 m² g^-1), and small porosity (ranging from 0.6 to 3.4 cm³ g^-1 ). Sorption of toluene vapor on NOMs was found to reach equilibrium in about one hour. A weak interaction (van der Waals' forces) was found between toluene and the three NOMs, with sorption uptake in the order of peat-CH > compost TB > peat HS. This toluene uptake order is similar to that for pore volume. Compared to the pore size distribution data measured by liquid nitrogen, sorption of toluene vapor onto the model NOMs may be attributed to the mechanisms similar to that for nitrogen adsorption, suggesting that nitrogen may be used as a probe for determining the sorption of toluene on the three NOMs. For peat HS and compost TB, the sorption processes may be regarded as 'pore-filling' in a glassy phase SOM. In addition, based on the functional group composition analysis with CP/MAS- ¹³C-NMR, it was not aromatic carbon group but the alkyl carbon group that probably supplied a more flexible space (rubbery phase SOM) for toluene to penetrate. This flexible space may contribute somewhat to the sorption capacity so that the uptake of toluene by peat CH is higher than that of nitrogen.