Adsorptive removal of dye crystal violet onto low-cost carbon produced from Eichhornia plant: kinetic, equilibrium, and thermodynamic studies

Eichhornia charcoal is used as a potential adsorbent to remove dye crystal violet (CV) from aqueous solutions. Material was characterized for its surface chemistry by elemental analysis, Boehm titrations, point of zero charge measurements, Brunauer–Emmett–Teller, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Adsorption conditions were optimized by considering the effect of contact time, pH, initial concentration of the dye, and temperature. It is surmised that adsorption of CV increases with increase in pH, temperature, amount of adsorbent, ionic strength, and contact time. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Temkin, Dubinin and Radushkevich and generalized isotherms models. Adsorption kinetics were contemplated using pseudo-first order, pseudo-second order, intraparticle diffusion, Elovich model, and Bangham’s model. Equilibrium adsorption of CV was better explained by Langmuir adsorption model and evidenced the maximum adsorption capacity as 58.13 mg g−1. Higher coefficient of determination (R2 > 0.99) and better agreement between the qe,cal and qe,exp values suggested that pseudo-second-order kinetic model better represents the kinetic adsorption data with rate constant 0.011, 0.015, and 0.024 g mg−1 min−1 at 303, 313, and 323 K, respectively. The energy of activation for the present system was found to be 31.82 kJ mol−1. Thermodynamic parameters manifested that adsorption process is spontaneous and endothermic in nature.