Interaction Mechanisms and Predictive Model for the Sorption of Aromatic Compounds onto Nonionic Resins

Abstract

Understanding interaction mechanisms between porous sorbents and organic compounds is important in selecting or custom-synthesizing an appropriate sorbent. In this study, sorption isotherms of a set of 14 (XAD-4&7) or 11 (MN200) aromatic compounds were measured for three nonionic resins, and a phase conversion approach (from aqueous phase to n-hexadecane or gas phase) was applied to separate sorbate-sorbent interactions from the overall involved interactions. Subsequently, contributions of individual interactions to the overall ΔG were quantified by poly parameter linear free energy relationships (pp-LFERs). Cavity energy (V), energy costs for creating cavities in bulk water, is the dominant driving force for the sorption from aqueous phase. Meanwhile, sorption was substantially abated by H-bonding accepting capacities of the solutes (B) due to the high electron accepting capacity of water molecules. Solute’s H-bonding donating capacity (A) and polarity/polarizability (S) are predominantly responsible for the n-hexadecane or gas-phase converted sorptions; V is also important in the gas-phase converted sorption. XAD-7 has larger A and S coefficients than XAD-4 and MN200 for both the original and converted analyses, while the opposite is true for V coefficients. More promisingly, a predictive model, developed based on the sorption of 7 simple aromatic compounds by the resins, can accurately estimate the sorption behaviors of 7 other relatively complex aromatic compounds within a wide range of concentrations.