Investigation of adsorption performances of green walnut hulls for the removal of methylene blue

Abstract

Green walnut hulls are agricultural wastes released in vast amounts in Turkey. In this study, green walnut hulls were used, without complex preparation, for the adsorption of methylene blue from an aqueous medium. The influence of the optimum pH, initial dye concentration, adsorbent dose, and agitation time on adsorption was explored. Optimal experimental conditions were detected to be pH 10, 0.5 g/L of the adsorbent dose with 1,440 min of agitation time. The experimental data complied with the Langmuir isotherm model, indicating chemisorption. According to this model, the adsorbent capacity was 1,000 mg/g, and this process followed the pseudo-second-order kinetic model. According to the thermodynamic investigation, the adsorption process of methy-lene blue on green walnut hulls was exothermic, feasible, and spontaneous. Desorption studies and analytical applications were also executed. The usage of green walnut hulls ensures not only reduced green walnut hulls wastes for environmental safety, but also provides a cheap and abundant adsorbent for dye removal.