Method to calculate the adsorption free energy of a pollutant as function of temperature Alhadji Malloum 1,2 , Jeanet Conradie 1 1 Department of Chemistry, University of the Free State, South Africa, 2 Department of Physics, Faculty of Science, University of Maroua, Cameroon Adsorption is one the techniques used in wastewater treatment, which is affordable and easy to implement. The aim of adsorption is to identify cheap and abundant materials to adsorb pollutants 1 . Up to now, most of the works performed on the adsorption of pollutants are based on experimental investigations, which is desirable. However, experimental investigations are slow and require considerable resources (both human and financial). Molecular modeling can considerably speed up the discovery of materials with high adsorption capacity for wastewater treatment. Despite considerable efforts in computational studies, the molecular modeling of adsorption processes has several limitations in reproducing experimental conditions. Handling the environmental effects (solvent effects) and the temperature effects are part of the important limitations in the literature. In this work, we address these two limitations using the adsorption of phenol onto coronene as case study. In the proposed model, for the solvent effects, we used a hybrid solvation model, with n explicit water molecules and implicit solvation. We increasingly used n=1 to n=12 explicit water molecules. To account for the temperature effects, we evaluated the adsorption efficiency using the adsorption free energy for temperatures varying from 200 to 400 K. We generated initial configurations using classical molecular dynamics, before further optimisation at the wB97XD/aug-cc-pVDZ level of theory. Polarizable continuum solvation model (PCM) is used for the implicit solvation. The adsorption free energy is evaluated to be -1.3 kcal/mol at room temperature. It has been found that the adsorption free energy is more negative at low temperatures. Above 360 K, the adsorption free energy is found to be positive 2 . References 1. Cam, L. M.; Van Khu, L.; Ha, N. N. Theoretical study on the adsorption of phenol on activated carbon using density functional theory, J. Mol. Model. 19 (2013) 4395--4402. 2. A. Malloum, J. Conradie, Adsorption free energy of phenol onto coronene: Solvent and temperature effects, J. Mol. Graph. Model. 118 (2023) 108375.
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