Kinetics, equilibrium and thermodynamics studies of C.I. Reactive Blue 19 dye adsorption on coconut shell based activated carbon

Abstract

In this work, low cost coconut shell based activated carbon (CSAC) was produced from agricultural wastes for the kinetics, equilibrium and thermodynamics studies of Reactive Blue 19 (RB19) dye adsorption from aqueous solution. CSAC was characterized using the UV/visible spectrophotometer, Fourier transforms infrared spectroscopy (FT-IR), field emission dual beam-scanning electron microscopy/focused ion beam (FES-SEM/FIB). Batch adsorption experiments were conducted to examine the effects of contact time (10–50 min), initial dye concentration (10–50 mg/L), pH (3–12), and solution temperatures (28°C–80 °C) on the dye removal. Thermodynamic analysis shows the standard Gibb's free energy change (ΔG°) to have negative values, confirming the feasibility and spontaneity of the process. The changes in enthalpy (ΔH°) and entropy (ΔS°) were found to be 7.771 kJ/mol and 0.035 kJ/mol K, respectively. Equilibrium data were fitted to Langmuir and Freundlich isotherm models with good correlation coefficients and coefficient of determination. The kinetic data were fitted to pseudo-first-order rate law, pseudo-second-order kinetics, and intra-particle diffusion model. The experimental data were found to have the best agreement with the pseudo-second-order kinetic model. Activation energy, (Ea) was evaluated as 57.84 kJ/mol. The specific adsorption rate constant, k2 increased virtually 39-fold when temperature was raised to 80 °C.