Single and binary adsorption of sulfonamide antibiotics onto iron-modified clay: linear and nonlinear isotherms, kinetics, thermodynamics, and mechanistic studies

Iron-modified raw kaolinite clay (Fe-MC) was synthesized by co-precipitation method, characterized, and then applied as a low-cost adsorbent to sequester sulfachloropyridazine (SCP) and sulfadimethoxine (SDM), emergent water contaminants, from aqueous media by batch equilibration at circumneutral pH. The adsorption rate was kinetically described by the pseudo-second-order model. Equilibrium monocomponent sorption data were fitted to three two-parameter linear and nonlinear isotherm models. The data were best described by Temkin and Langmuir nonlinear equations. Linearization of adsorption isotherms is demonstrated to be an unsuitable analytical tool for predicting adsorption isotherms. The Langmuir monolayer maximum adsorption capacities were 4.561 and 1.789mg/g for SCP and SDM, respectively. The binary adsorption study showed an antagonistic adsorption process of SCP (R-q,R- SCP=0.625) in the presence of SDM (R-q,R- SDM=1.032). The thermodynamic parameters, namely enthalpy (H), Gibbs free energy (G), entropy (S), Arrhenius activation energy (E-a), and sticking probability (S-*), indicated that the processes are spontaneous, exothermic, and physical in nature. The adsorption process was attributed to hydrogen bonding and negative charge-assisted H-bonding (CAHB). Using the Langmuir isotherm, the amount of Fe-MC required for a given volume of effluent of known contaminant concentration could be predicted. [GRAPHICS] .