Modification of sodium montmorillonite by two quaternary ammonium surfactants with different chain lengths: Preparation, characterization and adsorption of acetaminophen

The objective of this study is to synthesize and characterize two types of organic montmorillonites, namely H-Mt and O-Mt, through the modification of sodium montmorillonite (Na-Mt) using quaternary ammonium salt surfactants, specifically hexadecyl dimethyl benzyl ammonium chloride (HDBAC) and octadecyl dimethyl benzyl ammonium chloride (ODBAC). And the application of H-Mt and O-Mt as acetaminophen (PCT), an adsorbent for an emerging pharmaceutical contaminant, in wastewater treatment was investigated. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD) results demonstrated the successful intercalation of both modifiers into Na-Mt. The intermittent adsorption experiments demonstrated that the optimal dosages of H-Mt and O-Mt modifiers were 1.6 CEC and 1.0 CEC (CEC is the cation exchange capacity of Na-Mt), respectively. The saturated adsorption capacities of PCT reached 25.9087 mg/g (H-Mt) and 14.7313 mg/g (O-Mt) at pH 5, respectively, while the original Na-Mt exhibited a significantly lower adsorption capacity of only 0.7668 mg/g. Additionally, it was observed that the adsorption capacity of O-Mt on PCT was inferior to that of H-Mt, suggesting that the longer alkyl hydrocarbon chain has a larger steric hindrance during the adsorption process, which prevents PCT from entering the adsorption site in the organic montmorillonite. The adsorption of PCT by two types of organic Mt was more accurately described by the pseudo-second-order kinetic model and the Freundlich adsorption isotherm equation. The negative Δ G° values and negative Δ H° values determined by the thermodynamic parameters study confirmed that the adsorption of PCT on H-Mt and O-Mt was a spontaneous exothermic process. The present study validated the potential of Na-Mt functionalized with HDBAC and ODBAC as a highly effective adsorbent for emerging pharmaceutical contaminant.