Biosorption of dye crystal violet on Tragopogon sp. leaf powder: Equilibrium, kinetics, thermodynamics, and DFT calculations

Crystal violet, CV, was adsorbed on dead mass of Tragopogon sp. in aqueous solutions and the adsorption process was evaluated by analytical, visual, and theoretical means. The functional groups on the biosorbent surface were detected by FT-IR (Fourier Transform Infrared Spectrophotometry), and the surface morphology was visualized by SEM (Scanning Electron Microscopy), and EDX (Energy Dispersive X-Ray Analysis). Some of the biosorption conditions, pH, time, adsorbent mass, and temperature, were optimized. Three isotherm models, Langmuir, Freundlich, and Dubinin-Radushkevich, employed for the understanding of the reaction kinetics, suggested a spontaneous endothermic reaction that took place on the surface of Tragopogon sp cells. Iterative usability experiments, involving four biosorption-desorption rounds, showed that Tragopogon sp. biomass retained approximately 42% of its sorbent activity. Calculations, using the Gaussian software packages B3LYP, HF, and M06-2x, indicated a very high biosorption capacity of Tragopogon sp. for crystal violet. Crystal violet had -7.2067 HOMO and 0.1921 LUMO values.