Enhanced cationic dyes adsorption: Experimental and theoretical insights into Moroccan clays vs. commercial montmorillonite

The adsorption of cationic dyes, such as crystal violet (CVD), is particularly important due to their widespread use in industrial sectors like textiles, paper, and plastics, leading to significant environmental discharges, especially in wastewater. This study assesses the potential of Moroccan clays as adsorption agents for crystal violet dye (CVD), a cationic dye that poses a serious threat to aquatic ecosystems. Three types of clays, natural red clay (RC), gray clay (GC), and commercial Montmorillonite (MMT-K10). These clays were thoroughly characterized using techniques such as scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), zeta potential (zeta potential) analysis, and BET surface area. Batch experiments were conducted to evaluate the impact of various parameters on the CVD adsorption process, including adsorbent quantity, pH, contact time, and temperature, followed by isothermal, kinetic, and thermodynamic analyses. The results indicate that adsorption equilibrium is reached within one hour for all clay types, and the process is well-described by the pseudo-second-order model. The adsorption data for natural red fit the Freundlich model better, while the Langmuir models are suitable for gray clay and Montmorillonite, with respective maximum adsorption capacities of 47.62 mg g- 1, 42.56 mg g- 1, and 171.25 mg g- 1. Thermodynamic studies indicate that the adsorption processes are endothermic, physically driven, and occur spontaneously. RC and GC exhibit desorption rates of 63.94 % and 60.93 %, respectively, and demonstrate the capability to undergo regeneration for up to five cycles. Density functional theory (DFT) analysis was conducted using the B3LYP/ 6-31+G(d,p) model, incorporating solvent effects via the Polarized Continuum Model (PCM), revealing non- covalent interactions through Multiwave function analysis and visualization with Visual Molecular Dynamics (VMD) software. Monte Carlo (MC) simulations and non-covalent interaction (NCI) models further elucidated the surface interactions between the clays and CVD. These results highlight the potential of natural clays as costeffective alternatives to commercial adsorbents, offering promising prospects for sustainable water treatment strategies.