Effect of Brønsted acidity of HY zeolites in adsorption of methylene blue and comparative study with bentonite.

Abstract

In the present study, HY zeolite with various Si/Al ratios have been used as adsorbents for the removal of a cationic dye; methylene blue, from aqueous solution using a batch process, and a comparative study with bentonite was conducted. Characterizations of the adsorbents were carried out by nitrogen adsorption–desorption, pyridine chemisorption followed by infrared spectroscopy and X-ray fluorescence. The effects of various parameters such as contact time, initial MB concentration, adsorbent concentration and solution pH were investigated. The adsorption of methylene blue on the zeolites is directly related to the Brønsted acidity where each molecule of MB corresponds to one Brønsted acid site. This means that the adsorption mechanism occurs via a cation exchange. So, adsorption of MB can be used to determine the Brønsted acidity of HY zeolites. The highest removal efficiency (181 mg g−1) corresponding to 86% of the abatement rate has been obtained with the bentonite. At lower dye concentrations (≤ 50 mg L−1), HY (16.6) and bentonite have a close adsorption capacities, 93 mg g−1 (97%) and 96 mg g−1 (99%) respectively. For both material types, the pseudo-second-order kinetic model fits very well with the experimental data. Equilibrium data fitted well the Langmuir isotherm model in the studied concentrations range of MB.