Adsorption of Linuron by the chitosan-bentonite composite: Kinetic, thermodynamic, and theoretical studies

Abstract

There is an increasing need for research on the use of cost-effective materials to decontaminate wastewater polluted with Linuron. In this context, we investigated the application of a chitosan-bentonite composite for the removal of Linuron from aqueous solutions. The experiments were conducted in batch mode under varying experimental conditions. Adsorption was examined as a function of mass ratio, adsorbent amount, initial herbicide concentration, contact time, and pH. The Langmuir and Freundlich models were applied to analyze the results, while the kinetics were described using the pseudo-first and pseudo-second-order models. The results indicated that the Langmuir model provided a better fit for Linuron adsorption, whereas the pseudo-first-order model more accurately described the kinetics at the optimum pH. On the other hand, the molecular geometry of Linuron in aqueous solutions was determined using the Density Functional Theory (DFT) method at the B3LYP/6-311+g(d,p) level of theory, along with the Conductor-like Polarizable Continuum Model (CPCM) solvation model. The global chemical reactivity indicators were calculated based on the frontier molecular orbitals. Local reactivity indices were determined using Mulliken charges, natural population charges, and Fukui functions. Furthermore, the optimal adsorption configuration of Linuron molecules was identified to accurately estimate the energy involved and ensure the success of the adsorption process. To analyze and calculate adsorption energies, a model was developed to represent the interaction between the adsorbed molecule and the clay surface. The Monte Carlo (MC) method was used to thoroughly examine the configuration. The presence of strong interactions and negative adsorption energies indicates that Linuron molecules are attracted to and stable at the interface. Molecular dynamics (MD) simulations further validated the robustness of the results.