Abstract
A novel adsorption model for the description of adsorption isotherms of cobalt nitrate on porphyrins H2TPP and H2TTPP is developed in the present paper. Experimental data were measured at five temperatures using the quartz crystal microbalance technique and were discussed to choose the most reproductive adsorbent for the achievement of the vitamin B-12 nucleus. Then, the modeling treatment was established based on the grand canonical formalism in statistical physics by taking into account the lateral interaction between the adsorbate particles. This leads to a six parameter equation describing the complexation process at the molecular level. Actually, there is a good correlation between experimental data and those calculated by using the double-layer L.B.L. model. It was found that cobalt ions were adsorbed via a multi-docking mechanism onto the two adsorbents. The study of the density of receptor sites (P-M) confirmed the endothermic nature of the two complexation processes. The van der Waals parameters indicated that the disturbances following the lateral interactions between the adsorbates are the highest in the case of tetraphenylporphyrin. The magnitude of the calculated adsorption energies reveals that cobalt is physisorbed onto tetraphenylporphyrin, whereas chemical forces were found in the case of porphyrins (H2TTPP). In addition, the proposed model allows the prediction of some adsorption thermodynamic functions, which govern the adsorption mechanism, such as entropy, Gibbs free enthalpy, and internal energy.