Chemisorptive removal of a synthetic dye from single and binary basic dye systems using sawdust of locust bean tree: Isotherm, kinetics, error function and thermodynamics

Abstract

Adsorptive properties of sawdust of locust bean tree, an agrowaste toward the removal of methylene blue from single and binary dye systems in aqueous solution is investigated so as to determine the effects of the composition of the solution on adsorption process. The sawdust was characterized using Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) spectrophotometry, X-Ray diffraction and pH point of zero charge. Batch adsorption experiments were carried out to investigate the effects of adsorbent dose, solution pH, contact time, initial dye concentration and temperature on the dye adsorption. The equilibrium data obtained were subjected to Langmuir, Freudlich, Temkin and Harkin- Jura isotherm equations. The data on kinetics were tested with pseudo-first order, pseudo-second order and Weber-Morris equations, while the thermodynamics of the sorption processes were also studied. The adsorption isotherm in all the dye systems follow Freundlich model. The adsorption process in single and binary dye systems is well described by both pseudo first order and pseudo second order kinetics. All the adsorption processes were spontaneous, endothermic and with increased randomness (+ve DS).