文摘
Based on a combination of Density Functional Theory (DFT) and Surface Complexation Modeling (SCM), a general mechanism is suggested for (a) the interaction of non-polar S-containing pesticides, Methyl/Ethyl-Parathion, Fenthion, Methidathion, and Thiram with carbonates in solution and (b) their adsorption on chargeable oxides. Surface Complexation Models show that in the presence of carbonates, the species [pesticide-HCO3?/sup>] is formed in solution. At pH 5-7, the convolution of the pH-dependence of the [pesticide-HCO3?/sup>] concentration with the pH-dependent concentration of the {?#xA0;XOH2+} sites of a-Al2O3 determines the pH profile of the adsorption. The Density Functional Theory calculation for Methyl-Parathion and Thiram reveals that a significant fraction of negative charge is accumulated on the S-atoms of the pesticides while a net positive charge is localized on the -CH3 groups. Thus the combination of -CH3 and S is ultimately responsible for the charge imbalance on these pesticides.