Adsorption–desorption behavior of naphthalene onto CDMBA modified bentonite: Contribution of the π–π interaction

To enhance the removal of aromatic hydrophobic contaminants and to explore the π–π interaction between solute and adsorbent, organoclays modified with an aromatic long-chain alkyl surfactant, cetyldimethylbenzylammonium (CDMBA), were synthesized in this study. The adsorption–desorption behavior of naphthalene (NA) onto the resultant CDMBA-Bent (organoclays modified with CDMBA) was studied using batch-adsorption experiments. ructural characteristics of organobentonites were studied using X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR). The interlayer surfactant of CDMBA-Bent adopted similar packing pattern to that of CTMA-Bent (organoclays modified with CTMA), and the alkyl chain packing density of CDMBA-Bent was lower than that of CTMA-Bent under the same surfactant loading. The adsorption coefficients (koc) of CDMBA-Bent towards NA were about 1.6 times higher than those of CTMA-Bent at all surfactant loadings tested. All desorption isotherms of NA from both CDMBA-Bent and CTMA-Bent showed hysteresis. The hysteresis index (calculated as kD/kA) of NA by CDMBA-Bent was much lower than that by CTMA-Bent, indicating a higher extent of irreversibility. A strong electron donor–acceptor interaction was explored between the aromatic rings of CDMBA and NA by 1H-NMR analysis. This specific π–π interaction may account for the high adsorption capacity and irreversibility of NA onto CDMBA-Bent. These results offered new insights of the adsorption mechanism of NA onto organoclay.