Coconut coir dust as a low cost adsorbent for the removal of cationic dye from aqueous solution

Adsorption of methylene blue from aqueous solution onto coconut coir dust (CCD) a low cost agricultural waste material in a batch process was investigated. Adsorption was studied as a function of amount of adsorbent, pH and concentration with time. It was found that percentage adsorption varied linearly with the amount of adsorbent and concentration with time but varies non-linearly with pH. Adsorption equilibrium data were represented by isotherm, kinetics and thermodynamics models. Three isotherm models namely Langmuir, Freundlich and Temkin were tested and adsorption was found to fit well into these models with R2 ⩾ 0.90. The kinetic data were well described by the pseudo-second order kinetic model. The adsorption process was endothermic with a mean change in enthalpy (ΔH) (+17.87 KJ mol−1) and spontaneous with a mean free energy change (ΔG) (−9.69 KJ mol−1). FTIR analyses of the adsorbent suggest that adsorption of the dye was through a chemical interaction of the functional groups on the surface of the adsorbent.