Enhancement of Nigerian Montmorillonite Clay Mineral by HDTMA+ and TMPA+ Cation Intercalation for Multi-Component Adsorption of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) in Aqueous Solution

This study investigates the enhancement of Nigerian montmorillonite clay through intercalation with hexadecyltrimethylammonium (HDTMA⁺) and trimethylphenylammonium (TMPA⁺) cations for the adsorption of benzene, toluene, ethylbenzene, and xylene (BTEX) from aqueous solutions. The modified clays, Mt-HDTMA and Mt-TMPA, were characterized for physicochemical properties, revealing increased hydrophobicity and cation exchange capacity. Batch adsorption experiments demonstrated that Mt-HDTMA exhibited higher adsorption capacities (7.73–12.95 mg/g) compared to Mt-TMPA (5.81–9.73 mg/g), attributed to the longer alkyl chain of HDTMA⁺ enhancing hydrophobic interactions. Kinetic studies indicated that adsorption followed a pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm analysis revealed that the Freundlich model best described the adsorption process, indicating multilayer adsorption on heterogeneous surfaces. Thermodynamic studies confirmed the endothermic and spontaneous nature of BTEX adsorption, with Gibbs free energy (ΔG) values becoming more negative at higher temperatures. Density functional theory (DFT) calculations supported experimental findings, showing stronger adsorption energies for Mt-HDTMA (-34.56 to -40.15 kJ/mol) than Mt-TMPA (-28.74 to -34.67 kJ/mol), with xylene exhibiting the highest affinity due to π-π interactions. These results highlight the potential of surfactant-modified montmorillonite as an efficient and cost-effective adsorbent for BTEX removal from contaminated water, with HDTMA+-modified clay showing superior performance.