Adsorption of single and mixed colors by kaolinite clay: Experimental research combined with a theoretical examination using DFT

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Adsorption of the most suitable dyes on locally available clay minerals is considered the most promising, efficient, and inexpensive approach. Indeed, the main objective of this study was to explain the selectivity of an adsorbing surface between the two dyes in a mixture of a solution, using a density functional theory (DFT) calculation based on the global electrophilic index ω of the evaluated cationic dyes. Thus, to study the effect of adsorption of these two dyes, Basic Yellow 28 (BY28) and Malachite Green (MG), in a mixture, and separated by a kind of natural clay from the city of Safi, composed mainly of Kaolinite, determined using structural and textual analysis DRX., FTIR., XRF., SEM., EDX., pHZPC. Subsequently, the study of the effect of different parameters, such as the dose of adsorbent, concentration, pH, and the temperature of the work, allows for optimizing working conditions. The experimental data were analyzed using the isothermal, Langmuir, Temkin, and Freundlich models. The Langmuir model obtained the best fit with a maximum monolayer adsorption capacity of 28.41 mg.g−1 for basic yellow 28, and 23.75 mg.g−1 for the malachite green in the mixture. The adsorption of the mix was found to be of a different nature (ΔH°BY28.mixt = -13.37 KJ.mol−1, ΔH°MG.mixt = 9,82 KJ.mol−1), while the positive value for MG.mixt of entropy 66.7 J.mol−1.K−1 indicated increased randomness at the solid/liquid interface. The adsorption kinetics data were correctly fitted with the pseudo-second-order kinetic model. Local Parr functions were used to accurately describe the most reactive adsorption sites, and the most selective dye was then assessed.