Effect of structural variations on sorption and desorption of phenanthrene by sediment organic matter

Sorption and desorption isotherms of phenanthrene (PHE) on sediment organic matter (SOM) prepared at different combustion temperature were studied to examine the impact of SOM structure on sorption and desorption. With the increase of combustion temperature from 0 to 400°C, the aromatic groups (-CC) in SOM samples increased, while the aliphatic groups (-CH, -CH(2)) and polar structures (-C-O, -OH) decreased. When the combustion temperature increased to 500°C, aliphatic structures, polar structures and most aromatic structures were burnt out, and the mineral materials were dominant in the sample. The increase of combustion temperature decrease the sorption isotherm nonlinearity index n value, and enhanced the adsorption capacity and desorption hysteresis for PHE on SOM. However, higher n value, lower sorption capacity and sorption irreversibility were presented in the sample treated at 500°C (T500). Positive correlations between single-point organic carbon-normalized distribution coefficient log K(oc) values and aromatic carbon (p<0.01) and negative correlations between log K(oc) values and aliphaticity or H/C ratios (p<0.05) were observed. There was a negative relation between hysteresis index (HI) value and aromatic carbon (p<0.01) and a negative trend of the sorption isotherm nonlinearity index n values and aromatic carbon (p<0.01). The above results indicated the dominance of aromatic structures in the sorption nonlinearity, sorption capacity and desorption hysteresis of PHE on SOM.