Statistical physics modeling of synthetic dyes adsorption onto Spirulina platensis nanoparticles

Experimental adsorption of synthetic dyes, FD&C red no. 40 and Tartrazine, onto Spirulina platensis has been analyzed using a statistical physics treatment at different temperatures (298, 308, 318, and 328 K) and at different values of pH (4, 6, and 8). The statistical physics formalism was used to develop the analytical expressions of models. The interpretation of the adsorption of these dyes on Spirulina platensis was achieved by choosing the adequate model and by presenting the evolution of the parameters involved in the analytical expression of this model such as the number of adsorbed dye molecules per site (n_d), the receptor sites density (D_r), the adsorbed quantity at saturation (q_s), and the molar adsorption energy (ΔE). Thus, several interpretations and results describing the adsorption of dyes on Spirulina platensis are extracted regarding the behaviors of these parameters at different temperatures and different values of pH. Thermodynamic functions such as the Gibbs free energy, the internal energy, and the entropy are studied at different values of pH.