Physicochemical Characterization of Clay and Study of Cationic Methylene Blue Dye Adsorption

Abstract

In an attempt to examine novel adsorbents in accessing an ideal adsorption system, this study aimed to help understand the main and secondary characteristics of a Moroccan natural clay. X-ray fluorescence, infrared, and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis (SEM-EDX) were used for the identification. The findings demonstrate that this Clay is composed of a mixture of quartz, calcite, magnetite, and Rutile in very high proportions. SEM revealed the presence of clay grains in the presence of fine particles and irregularly contoured sticks. The results of semiquantitative detection by EDX also reveal the presence of certain mineral species (Si, Al, Mg, Fe, K, Cl, S, Ca, and Na). The exploited kinetic technique was achieved using two different kinetic models: first- and second-order rate laws. Commensurate to the obtained results, the 2-sec order model better described the adsorption of dye MB onto the natural clay. The results confirmed that the adsorption process followed the Langmuir model with the high coefficient correlation obtained which are very close to 1. In the sequel, DFT results revealed that the HOMO and LUMO surfaces of the methylene blue dye are mostly distributed on all dye parts, reflecting possible strong interactions with the clay. The quantum descriptors investigated in this study identify the most nucleophilic and electrophilic centers that can be used to suggest a suitable mechanism for the adsorption of the dye by the clay. The values of enthalpy ΔH 0 and entropy ΔS 0 of activation were −15.88 kJ mol–1 and −0.021 J mol–1 K–1, respectively, show that the nature of the adsorption process of MB on clay is exothermic and the order of distribution of the dye molecules on the adsorbent increases with respect to that of the solution so the negative values of ΔG 0 (from −9. 62 to −8.99 kJ mol–1) indicate that the adsorption process is spontaneous.