Adsorption isotherm modeling of carbendazim and flumetsulam onto homoionic-montmorillonite clays: comparison of linear and nonlinear models

This study deals with the adsorption of two pesticides, carbendazim and flumetsulam, from aqueous solutions onto four homoionic-montmorillonite clays (Ag , Zn , Cu , and H) . Equilibrium adsorption isotherm data were analyzed using Freundlich, Dubinin–Radushkevich, and Temkin isotherms. Linear and nonlinear fitting methods were compared to determine the best-fitting isotherms for the experimental data. Three error analysis methods were used to evaluate the data for each method: the coefficient of determination (R) , sum of squared errors (SSE), and chi-square test (χ) . Equilibrium adsorption isotherms exhibited that the carbendazim adsorption mainly involved cation exchange with homoionic-montmorillonite adsorbents. However, for flumetsulam, the main mechanisms were possibly the cation bridging by Ag , Zn , and Cu cations and the surface complexation reactions of the adsorption on homoionicmontmorillonite (H) adsorbent. The modeling results showed that the nonlinear Freundlich model could fit the data better than the Dubinin–Radushkevich or Temkin models, with relatively higher R and smaller SSE and χ values. Thus, the nonlinear method is a better way to obtain the isotherm parameters.