Experimental and Theoretical Study of Methylene Blue Adsorption on a New Raw Material, Cynara scolymus—A Statistical Physics Assessment

Abstract

Methylene blue (MB) adsorption was performed on a natural material powder of Cynara scolymus as a new inexpensive adsorbent identified by Cs. To analyze the Cs material, FTIR, SEM, isoelectric point (pHpzc) analysis, TGA, and DRX were used. The maximum experimental adsorption capacity of the Cs material was 203.333, 192.187, and 179.380 mg•g−1 at 298, 303, and 313 K, respectively. The correlation coefficients (R2) and average percentage errors APE (%) values for the kinetic and isotherms models indicated that the adsorption kinetics followed a pseudo-nth order model and that the traditional isotherm model Redlich–Peterson (R–P) correctly described the experimental data obtained at 298, 303, and 313 K, respectively. The steric, energetic, and thermodynamic characteristics of the most relevant advanced model (double-energy single-layer model (AM 2)) were analyzed in detail. The number of active sites for the first receptors (n1) was determined to be 0.129, 0.610, and 6.833, whereas the number of second active sites (n2) was determined to be 1.444, 1.675, and 2.036 at 298, 303, and 313 K, respectively. This indicated the presence of both multi–docking and multimolecular modes for the first style of MB ions (n1), while only a multimolecular mode for the second style of MB ions (n2). Thermodynamic characteristics demonstrated that MB adsorption onto the Cs adsorbent is spontaneous and feasible.