Investigation of montmorillonite clay for its potential application for pesticides adsorption in single and binary systems

Single-compounds and binary experimental data on the adsorption of 2,4-Dichlorophenoxyacetic acid (2,4-D) and Acifluorfen (ACF) onto montmorillonite are obtained at different temperatures (30, 40, 50 °C) to explain and understand the competitive interactions between these water contaminants. The experimental results indicate that the maximum adsorption capacities of ACF in the single-compound system are approximately 90, 130, and 161 mg/g, respectively. In the binary system, these capacities decrease to 73, 114, and 142 mg/g, respectively. For 2,4-D, single-compound adsorption capacities varied from 55, 89 to 119 mg/g, while in binary system, they decreased to 44, 71 and 98 mg/g, respectively. The reduction in adsorption performance is related to the competitive effect between the investigated molecules. To further elucidate the adsorption mechanisms in single-compound and binary systems, a theoretical study based on modeling analysis is conducted. A double-layer adsorption model for single-compound and a competitive adsorption model for binary systems are employed to deeper investigate the possible mechanisms involved.

The results indicate that ACF is adsorbed via an aggregation process, forming trimers at lower temperatures (30 °C), whereas this aggregation is reduced at higher temperatures (50 °C), leading to monomer formation. In contrast, 2,4-D is removed without undergoing an aggregation process. Binary modeling revealed that the presence of a second compound in solution creates an antagonistic effect, leading to reduced adsorption capacities. This theoretical approach demonstrates that ACF and 2,4-D are adsorbed primarily through physical interactions, with endothermic processes playing a key role in their removal.