Isotherm Study of Anthracene Adsorption on Natural Zeolite and Zeolite Modified with CTAB and SDS Surfactants

This study investigates the adsorption of anthracene onto natural clinoptilolite zeolite and natural zeolite modified with the surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). Initially, anthracene solutions with varying concentrations (mg/L) were prepared in an ethanol-water solvent mixture at a ratio of 9 : 1. Their absorbance was measured using a UV spectrophotometer at 357 nm to establish a calibration curve. Subsequently, the adsorption of anthracene solutions on both unmodified and modified zeolites was measured and determined. The results indicated that anthracene adsorption on SDS-modified zeolite was greater than that on CTAB-modified zeolite, which in turn exhibited higher adsorption capacity than unmodified zeolite. Adsorption isotherms (qe versus Ce) plotted using Curve Expert and Excel software demonstrated that the adsorption process follows a monolayer adsorption model. Isotherm examinations revealed that the unmodified zeolite exhibited the most favorable fit with several two-parameter isotherms, encompassing Langmuir, Freundlich, Temkin, Jovanovich, and Elovich models, as well as with three-parameter isotherms such as Hill-Debuer, Frumkin, Fowler-Guggenheim, Kiselev, Reich-Peterson, Sips, Hill, Radke-Prausnitz, Koble–Corrigan, and with four-parameter models like Weber–Van Vliet, Fritz–Schlunder and Baudu. The CTAB-modified zeolite demonstrated the highest compatibility with two-parameter Dubinin–Radushkevich and three-parameter Frumkin isotherm, in addition to four-parameter Fritz–Schlunder and Baudu models. Similarly, the SDS-modified zeolite conformed best to two-parameter isotherms including Elovich, Langmuir and Jovanovich, as well as three-parameter models such as Kiselev, Dubinin–Astakhov, Jossens, Sips, Hill, and four-parameter models Weber–Van Vliet, Fritz–Schlunder, and Baudu.