Stereographic and energetic studies of acid blue 9 adsorption onto Spirulina platensis (strain LEB-52) based on statistical physics approach

Abstract

A monolayer model extended to two energy levels (monolayer model 2) has been developed to fit the adsorption isotherms of acid blue 9 on Spirulina platensis (Sp LEB-52). These isotherms were obtained at different values of pH and different temperatures. The adsorption isotherm modeling was based on a statistical physics approach. The evolutions of stereographic and energetic parameters involved in the model equation were presented in this work. The obtained values of nd₁ and nd₂ are always higher than unity, indicating that the adsorption of acid blue 9 molecules on Sp LEB-52 is a multimolecular adsorption. The highest adsorption capacity (Q_s = 1251.8 mg g⁻¹) is signaled at pH = 4 and T = 298.15 K. Furthermore, we have used the monolayer model 2 as local isotherm to determine the adsorption energy distribution (AED) and the pore size distribution (PSD). The adsorption energy values corresponding to active sites of type 1 and type 2 are, respectively, in the intervals [10.5 − 27.5 kJ mol⁻¹] and [15 − 25 kJ mol⁻¹]. Obtained PSDs indicate that acid blue 9 molecules are adsorbed on macro-pores of Sp LEB-52.

Keywords:

• Acid Blue 9
• Spirulina platensis LEB-52
• statistical physics
• adsorption energy distribution
• pore size distribution