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

Abstract

This study deals with the adsorption of two pesticides, carbendazim and flumetsulam, from aqueous solutions onto four homoionic-montmorillonite clays (Ag + , Zn 2+ , Cu 2+ , 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 (R2 ), sum of squared errors (SSE), and chi-square test (χ 2 ). 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 2+ , and Cu 2+ 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 R2 and smaller SSE and χ 2 values. Thus, the nonlinear method is a better way to obtain the isotherm parameters.