Effective adsorption of metals on porphyrins: Experiments and advanced isotherms modeling

Abstract

Abstract In this article, the investigation of the adsorption process of six metal compounds (aluminum chloride, aluminum sulfate, iron chloride, iron sulfate, indium chloride and indium sulfate) on the promising macromolecule named porphyrin was performed to prove new insights about the metals-porphyrin complexes. The experimental adsorption data of the six complexation systems were controlled at four reaction temperatures using the well-known microbalance apparatus (QCM). In fact, the experimental outcomes and the physical modeling treatment indicated that the complexation process of aluminium and iron should be analyzed via the mono-layer adsorption model whereas; the interaction between the two indium compounds and the porphyrin was described via the double-layer model. Actually, the physicochemical description showed that the three metals were adsorbed via a multi-docking mechanism. The fitted values of the paramount parameter density of the adsorbent sites showed the endothermic character of the studied processes. Thus, some porphyrin sites were activated only at high temperature. The down trend of the iron isotherms was explained through the van der Waals parameters which describe the lateral interactions influences. The calculation of the adsorption energies which describe the interactions between the adsorbates and the adsorbent showed that chemical bonds were carried out between the aluminum and the porphyrin. The thermodynamic study, through the two thermodynamic functions (the configurational entropy and the free enthalpy), showed that the disorder of the six processes is maximum at the level of the energetic parameters and that the six complexation mechanisms advanced spontaneously towards saturation. For the iron, the behavior of the enthalpy indicated that the lateral interactions between the adsorbates disfavored the adsorption of iron chloride and iron sulfate at high concentration. The double-layer process of the indium was confirmed by the trends of the free enthalpies which showed two stability states for the two indium compounds.