Biosorption of cationic dye from aqueous solutions onto lignocellulosic biomass (Luffa cylindrica): characterization, equilibrium, kinetic and thermodynamic studies

In the present study, biomass fiber (Luffa cylindrica) has been successfully used as biosorbent for the removal of a cationic dye namely, methylene blue, from aqueous solution using a batch process. The characterization of the biosorbent was carried out by the infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The chemical composition has been established by the energy dispersive X-Ray spectroscopy (EDS). The effects of various parameters such as the contact time (0–160 min), solution pH (2–10), biosorbent dose (0.5–8 g L^-1), particle size, initial MB concentration (20–300 mg L^-1) and temperature (20–60 ˚C) were optimized. The biosorption isotherms were investigated by the Langmuir, Freundlich, Dubinin–Radushkevich and Tempkin models. The data were well fitted with the Langmuir model, with a maximum biosorption capacity of 49.46 mg g^-1 at 20 ˚C. The kinetics data were analyzed by the pseudo-first-order and pseudo-second-order models. The mass transfer model in terms of interlayer diffusion was applied to examine the mechanisms of the rate-controlling step (R^2 = 0.9992–0.9999). The thermodynamic parameters: free energy (ΔG˚ = -5.428 to -3.364 kJ mol^-1), enthalpy (ΔH˚ = -20.547 kJ mol^-1) and entropy (ΔS˚ = -0.052 kJ mol^-1 K^-1) were determined over the temperatures range (20–60 ˚C). The results indicate that Luffa cylindrica could be an interesting biomass of alternative material with respect to more costly adsorbents used nowadays for dye removal