Preparation, characterization and application of a CTAB-modified nanoclay for the adsorption of an herbicide from aqueous solutions: Kinetic and equilibrium studies

In this study, surfactant-modified pillared montmorillonites (MMT) were prepared using cetyltrimethylammonium bromide (CTAB) by the intercalation method and used as adsorbent to remove bentazon from aqueous solutions. The main compositions of MMT and CTAB/MMT were characterized by Fourier transform–infrared spectroscopy (FT–IR), X-ray diffraction (XRD), scanning electron micrography (SEM) and energy dispersive X-ray (EDX) spectroscopy. The removal efficiency of bentazon was studied as a function of adsorbent dosage, pH, initial bentazon concentration and ionic strength (sodium carbonate, sodium bicarbonate, sodium sulfate and sodium chloride). The removal efficiency of bentazon by CTAB/MMT was more than that of MMT in similar conditions. By increasing adsorbent dosage and initial bentazon concentration, the removal efficiency was increased and declined, respectively. The results showed that the maximum adsorption of organo-modified montmorillonite was obtained at pH 3. The maximum adsorption capacity was estimated to be 500 mg/g at pH 3 and room temperature. The study of the adsorption kinetic model revealed that the pseudo-second order model was the best applicable one to describe the adsorption of bentazon onto CTAB/MMT. Adsorption data were analyzed by both Langmuir and Freundlich adsorption isotherms and the results showed that it was better described by the Langmuir model. The adsorption capacities of the samples were found to increase with Na₂CO₃ anion saturation, while they decreased in the presence of NaHCO₃, Na₂SO₄ and NaCl.