Effect of solution-ph on methylene blue dye adsorption on hydrogen titanate nanotubes processed via hydrothermal method

Abstract

Hydrothermally processed hydrogen titanate nanotubes (HTN) have been utilized for the removal of methylene blue (MB) dye from an aqueous solution via surface-adsorption mechanism. The HTN have been characterized using different analytical techniques such as the scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and Brunauer-EmmettTeller (BET) specific surface-area measurement techniques. The amount of MB dye adsorbed on the surface of HTN at equilibrium (qe ) has been examined as a function of contact time, initial dye-concentration, and initial solution-pH. A new model has been proposed to explain the observed variation in qe as a function of above variables. Within the investigated range of initial solution-pH (2.5–11), the MB dye adsorption on the surface of HTN has been observed to follow the pseudo-second-order kinetics with the dye-adsorption capacity of 105 mg • g–1observed at the initial solution-pH of ∼10. The adsorption equilibrium follows the Langmuir isotherm in a highly acidic solution (initial solution-pH ∼ 2.5) and Dubinin-Kaganer-Radushkevich (DKR) isotherm in a highly basic solution (initial solution-pH ∼11); while, within the intermediate range of initial solution-pH (∼7.5 and 10), it exhibits a transition from the Langmuir to DKR isotherm.