Study of the effect of variation in temperature and pH on the adsorption process of natural Gardenia yellow dye into TiO2 mesoporous for dye sensitized solar cells using the statistical physics formalism: Physicochemical and thermodynamic investigation

Abstract

In this paper, three adsorption isotherms of natural yellow Gardenia dye, at three different temperatures and at three pH values, were fitted by models established through statistical physics treatment. A double-layer model with two energies is able to give good fitting of these experimental data. Four physicochemical parameters are involved in the fitting of the experimental adsorption isotherms such as the number of adsorbed dye molecules per site n, the density of receptor sites Nm and the two energetic parameters C1 and C2. From the numerical simulation, the number of molecules per site showed that the adsorbate molecules have two anchorage positions parallel and nonparallel respectively when pH and temperature vary. The variation of the adsorbed quantity at saturation with temperature shows the exothermic nature of aggregation process of the natural Gardenia yellow dye. In the case of variation of pH, the acidic conditions are more favorable for the adsorption process. The numerical values of the calculated adsorption energies have revealed that the Gardenia yellow dye is physisorbed onto TiO2 mesoporous. A new method based on Kelvin equation in liquid phase has been developed to determine the pore size distribution (PSD) of TiO2 mesoporous in comparison with other experimental measurements. The result of PSD shows a significant effect of the variation with temperature and with pH values on the morphology of pore size structure. Finally, the calculated thermodynamic functions such as entropy, free enthalpy and internal energy exhibited that the system evolved spontaneously.