Organic cosolvent effects or sorption equilibrium at hydrophobic organic chemicals by organoclays

Isotherms were measured for sorption of naphthalene and diuron by four organoclays in equilibrium with various mixtures of methanol and water. The organoclays were prepared from Wyoming montmorillonite by replacing the natural exchangeable cations of the day by the quaternary ammonium ions TMA (tetramethylammonium), TMPA (trimethylphenylammonium), HDTMA (hexadecyltrimethylammonium), and BDTDA (benzyldimethyltetradecylammonium). TMPA-clay showed the greatest sorptive capacity for naphthalene, while BDTDA-clay was the most effective sorbent for diuron. The sorption mechanism for each sorbate-sorbent combination was related to the arrangement of the quaternary ammonium cations in the exchanged clay acid the volume fraction of methanol in solution (f(c)). As expected from the solvophobic theory, the linear sorption coefficients decreased loglinearly with increasing f(c) in the binary solvent mixture, except for TMPA-clay at f(c) > 0.5. In addition to solute-solvent and solvent-sorbent interactions, an additional effect involving solute-organoclay interactions influenced the sorption of naphthalene and diuron by organoclays from aqueous and mixed solvents.