| Adsorption of the herbicides atrazine, diuron, and simazine and metabolites DIA (de-isopropyl-atrazine) and DEDIA (de-ethyl-de-isopropyl-atrazine) were studied on an activated carbon fiber (ACF) using a batch test method. The specific surface area (1,217m2/g) and mean micropore width (1.24 nm) of ACF were determined by measuring the N2 adsorption at 77K (-196°C). Boehm's titration method and pH drift method were used to determine amount of surface functional group (total acidity: 238 meq/g and total basicity: 498 meq/g) and pHPZC (7.49), respectively. Single component adsorption and competitive binary adsorption isotherm experiments were conducted for low initial concentrations (20 ppb to 500 ppb). The Freundlich isotherm models described the single component adsorption process well (r 2 > 0.96 in all cases); however, there was a discrepancy between expected and observed adsorption capacities because of some uncertainty in Kow values of the solutes and differences in the geometry of the molecules. The Ideal Adsorbed Solution Theory (IAST) was used to describe competitive binary adsorption. The IAST was well adapted to describing competition involving the weakly adsorbed compounds (DIA and DEDIA), but the IAST proved less appropriate for describing competition among highly adsorbed compounds (atrazine, diuron, and simazine). |
