Kinetics and thermodynamics of enhanced adsorption of the dye AR 18 using activated carbons prepared from walnut and poplar woods

Abstract

Activated carbons prepared from walnut and poplar woods are used as economical adsorbents for the rapid removal and fast adsorption of Acid Red 18 dye from the aqueous solutions; the kinetics, isotherm and thermodynamics studies of the process were well investigated and elucidated. The adsorption phenomenon may be possibly attributed to the formation of various binding bonds between the activated carbons, developed from the poplar and walnut woods, surface and the dye molecules; adsorption may firstly take place on the external surface of the developed adsorbent i.e. activated carbon developed from the walnut and poplar wood particles, where the attached functional groups play a crucial role in the rapid removal and fast adsorption. Secondly, adsorption may take place on the entire surface, which leads to a uniform distribution of adsorbed Acid Red 18 molecules onto the developed adsorbents. Forces that are responsible for the main adsorption mechanism are π–π attraction between Acid Red 18 dye molecules and the CC bonds of the developed adsorbents. Consequently, at least three types of adsorption sites might occur on the adsorbent surface; these are basal plane, edge plane and micropores. Neither pseudo-first order kinetic model nor pseudo-second order kinetic model was able to describe the adsorption process of AR18 molecules onto the activated carbon from poplar wood.