Phenomenological statistical physics modeling of metalloporphyrins adsorption at the molecular level

Abstract

This paper is aimed to investigate the copper chloride and tin chloride adsorption phenomenon by using a quartz-crystal-adsorbent operating with both auspicious porphyrins: (i) the 5,10,15,20-tetrakis-(4-tolylphenyl)-porphyrin and (ii) the 5,10,15,20-tetraphenyl-porphyrin. Theobjectiveis to find out new insights about suitable adsorption materials used in the manufacture of metalloporphyrin. By means of the microbalance-(QCM)-method, the measurements of the equilibrium isotherms are done at six temperatures of adsorption (starting from 290 K to 315 K). Experimental observations have proven that, on the one hand, the copper chloride adsorption is performed through a mono-layer process, on the other hand, the tin chloride double-layer adsorption with the chloride ions’ participation is done via the layer by layer process. Referring to the experimental curves’ modeling, it has been shown that the two ions follow a multi-interaction procedure because the number of ions per adsorbent-site n is less than 1. Remarkably, the physicochemical-investigation of the four adopted models indicates that the tested porphyrins’ complexation-mechanism is an endothermic-process since the two steric-parameters (n and PM) increase along with the temperature increasing. Considering the investigation of the adsorption curves of H2TPP with the adsorption models including the a and b parameters (lateral interactions description), it is to be noted that the created metal-porphyrin(H2TPP) complex stability is the lowest one. The energetic-study reveals that the adsorption-energies |−ΔE1/2| of CuCl2 on H2TTPP, performed via a chemical adsorption mechanism, are greater than 40 kJ/mol and the adsorption mechanisms of the two ions on H2TPP, done through a physical process, present |−ΔE1/2| values inferior to 40 kJ/mol. Referring to the entropy, the enthalpy and the internal-energy, known as the three thermodynamic functions, the thermodynamic study shows that the four processes’ disorder is maximal at the energetic-parameters’ level and that the four complexation-mechanisms move-spontaneously to saturation. Considering H2TPP, the enthalpy behavior points out that the lateral-interactions between the adsorbates disfavor the copper chloride and the tin chloride adsorption at high concentration. The tendencies of the internal energies, which present two stability states corresponding to both adsorbents, affirm the tin chloride double-layer process.