Statistical and physical interpretation of dye adsorption onto low-cost biomass by using simulation methods

Abstract

In this work, statistical physics approach has been developed to investigate the adsorption of Basic Blue 3G dye onto low-cost biomass (coffee residues). Thermodynamic, energetic, and stereographic parameters controlling the dye adsorption were theoretically determined. Five models have been suggested as monolayers, double layers and three layers. Additionally, steric and energetic factors related to the adsorption process, such as the number of adsorbed molecules per site (n1, n2, n3), the receptor sites density (N1m, N2m, N3m), and the concentration at half-saturation have been taken into account. Thermodynamic potential functions such as internal energy Eint, entropy S and Gibbs free energy G have been analyzed and the selection of the models is coherently based on assumptions in good correlation with experimental conditions/findings. All the investigated parameters were deduced by using an adequate numerical fitting method. A detailed exploration of adsorption isotherms at microscopic scale was presented. The steric study explained the increase of the amount adsorbed at saturation as function of temperature. The discussion about energies showed that the adsorption was physical and exothermic, where the interactions are mainly of Debye and London type. The entropy quantification clearly demonstrated that the disorder increased before half-saturation and decreased after half-saturation, while the findings of free enthalpy and internal energy confirmed exothermicity and spontaneity.