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

•The adsorption capacity of CDMBA-Bent towards naphthalene was outstanding.•The adsorption process of naphthalene to CDMBA-Bent was irreversible.•The special π–π interaction was proposed to contribute to the adsorption affinity.

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.The structural 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.

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