Counterion Effects on the Adsorption of Acid Orange 8 from Aqueous Solution onto HDTMA-Modified Nanozeolite from Fly Ash

Surfactant-modified nanozeolites from coal fly ash were used for the removal of Acid Orange 8 (AO8) from water. The zeolitic material was modified by two cationic surfactants i. e., hexadecyltrimethyl ammonium bromide (HDTMA-Br) and hexadecyltrimethyl ammonium chloride (HDTMA-Cl). Both the modified nanozeolites were characterized using various techniques to obtain its physical and chemical constituents. The adsorbents before and after adsorption were characterized by X-ray diffraction (XRD). The dynamical data obtained at different concentrations for the two organozeolites fit well with pseudo-second-order kinetic model. The equilibrium adsorption data were interpreted in terms of the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. The results showed that the adsorption of AO8 was influenced by HDTMA-zeolite counterion. Zeolite modified with HDTMA-Br was most efficient than zeolite modified with HDTMA-Cl for AO8 removal. Negative values of Gibbs free energy change (ΔGo) for dye adsorption onto HDTMA-modified zeolites indicates that the adsorption process is spontaneous and thermodynamically favorable. As a result, surfactant-modified nanozeolites from coal fly ash could be used as effective adsorbents for AO8 removal from wastewater.