Methylene blue dye’s adsorption on a natural clay surface from Southeast Morocco: modeling and experimental equilibrium studies

Abstract

The present research work revolves around the evaluation of the elimination of the cationic dye Methylene Blue (MB) from an aqueous solution by the exploitation of natural clay (TMG) from South-East Morocco. Several physicochemical techniques were used to characterize our TMG adsorbate, namely: X-ray diffraction (XRD), Fourier transform infrared absorption spectroscopy (FTIR), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and zero charge point (pHpzc). The morphological properties and elemental composition of our material were identified using scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer (SEM-EDS). The batch technique was used under different operating conditions to produce quantitative adsorption, namely the amount of adsorbent, dye concentration, contact time, pH, and solution temperature. The maximum adsorption capacity of MB on TMG was 81.185 mg g-1 for a concentration of 100 mg L-1 MB at pHinitial= 6.43, temperature 20 °C, and 1 g L-1 adsorbent. The adsorption data were examined by Langmuir, Freundlich, and Temkin isotherms. The Langmuir isotherm provides the best correlation with the experimental data, and the pseudo-second-order kinetic model is more appropriate for the adsorption of the MB dye. The thermodynamic study of MB adsorption indicates that the process is physical, endothermic, and spontaneous. The Box-Behnken method was applied to identify the optimal conditions for MB removal in the design of batch experiments. The parameters examined result in >99% removal.