The study investigated the adsorption of sulfamethoxazole, a pharmaceutical water contaminant, on an adsorbent derived from reed canary grass. Adsorption isotherm data at different temperatures were analyzed by the Langmuir, Freundlich, Sips, Dubinin-Radushkevich, Fowler-Guggenheim, and Nitta isotherm models. Among the various isotherm models, Sips model simulated the experimental adsorption data slightly better with the least error, indicating a heterogeneous monolayer adsorption system with a maximum adsorption capacity of 147.9 mg/g and heterogeneity index of 1.15. Investigation of the Fowler-Guggenheim and Nitta models showed that interaction energy of adsorbed molecules was insignificant. Thermodynamic parameters were determined using Henry constants. Henery constants were 22.7, 17.5, and 10.8 L/g at 15celcius, 25celcius, and 35celcius. The change in enthalpy of adsorption was -27.5 kJ/mol, showing that the process is exothermic and physiosorption. The change in standard entropy was -23.2 J/(mol center dot K), suggesting a decrease in randomness during the adsorption process. Weighted mean of site energy distribution remained constant at 11.2 when adsorption temperature was increased from 15celcius to 25 celcius, and the weighted mean slightly decreased to 9.6 at 35 celcius, indicating weaker interactions at the higher temperature. The methodology used in this work to analyze interaction energy between adsorbed molecules can be transferrable to analyze data of adsorption of other pharmaceuticals or organics by various types of adsorbents.
