Computational study of acid blue 80 dye adsorption on low cost agricultural Algerian olive cake waste: Statistical mechanics and molecular dynamic simulations

The present study is focused on the adsorption of acid blue 80 dye on a low-cost sorbent, i.e. agricultural Algerian olive cake waste. FTIR analysis of the sorbent shows that the main compositional fractions are cellulose (cellobiose), hemicelluloses (xylose) and lignin. Batch isotherm studies are carried out under different experimental conditions in terms of temperature and pH. A subsequent FTIR spectrum analysis of the spent sorbent is adopted for a phenomenological interpretation of adsorption. Experimental adsorption isotherms show the presence of two steps, depending on the dye concentration. Adsorption isotherms are interpreted by statistical physics as well by molecular dynamics simulations. Based on statistical physics approach, a heterogeneous Bimodal-Gauss monolayer model is developed to evaluate the adsorption energy distribution and the isosteric heat of adsorption (Qst). The evaluations of adsorption energy distribution and Qst show that the interactions between adsorbent and adsorbate have greater magnitude than the adsorbate-adsorbate ones and aggregates of dye molecules are formed during the adsorption process. Furthermore, the heterogeneity of adsorbent is evaluated according the modeling approach showing that the temperature catalyzes the heterogeneity of surface and then different kinds of interaction occur during adsorption process. These interactions were identified by molecular simulations as Hydrogen, Van der Waals and electrostatic bonds. Finally, simulations results allow highlighting the lignin as the main compositional fraction of the sorbent responsible for adsorption of the investigated dye.