Application of advanced statistical physics modeling for the physicochemical analysis of adsorption isotherms of manganese (II) on porphyrins H2TPP and H2TTP

Abstract

A quartz crystal coated with porphyrins H2TTP and H2TPP was used to examine the adsorption mechanisms of manganese chloride and manganese nitrate. The experimental adsorption isotherms were performed at four temperatures (from 288 to 318 K) in order to compare the adsorption capacities of tetratolylporphyrin (H2TTP) and tetraphenylporphyrin (H2TPP). The experimental results demonstrated that manganese chloride and the porphyrin (H2TTP) are the adequate materials for ionophore fabrication. Then, theoretical investigation was established through statistical physics formalism in order to analyze the experimental isotherms on the ionic scale. A single-layer model was developed using the real gas law and was satisfactorily applied for the microscopic investigation of MnCl2 isotherms, indicating that the chloride ions have no impact on the complexation mechanism. The contribution of NO3− anions in the quadruple-layer adsorption of Mn(NO3)2 was interpreted via layer by layer formulation. Based on the physical significance of the two model parameters, the manganese adsorption was found to be typical of an endothermic phenomenon by the intermediacy of the steric parameters n and Pm. The interpretation of the van der Waals parameters a and b confirmed the highest stability of Mn(Cl)2-H2TTP among all complexes. Interestingly, the adsorption system manganese chloride-tetratolylporphyrin was recommended for ionophore application because it showed the highest adsorption energies involving chemical bonds during the complexation process. The single-layer model also allowed prediction of two thermodynamic functions (configurationally entropy and Gibbs free enthalpy) which govern the adsorption mechanism of MnCl2 on H2TTP. Graphic abstract: Chemical structure of manganese (II)—porphyrin complex: Ionophore nucleus [Figure not available: see fulltext.]