Application of Innovative Analytical Modeling for the Physicochemical Analysis of Adsorption Isotherms of Silver Nitrate on Helicenes: Phenomenological Study of the Complexation Process

Abstract

The interaction between the silver ion and the cyclic aromatic molecules, namely, the helicenes, is the subject of this paper. In fact, a silver complexation system based on quartz crystal microbalance (QCM) sensor with a functional film of helicenes has been designed and developed at four temperatures. The developed system, in which the sensor response reflects the adsorption of the hexahelicene and the heptahelicene, was able to control the complexed mass of silver for each concentration. Experimental outcomes indicated that the quartz crystal coated with heptahelicene is the adequate material for silver adsorption. Then, a theoretical study has been performed through two statistical physics models (SMPG and SMRG) in order to analyze the experimental adsorption isotherms of the two helicenes at the ionic scale. The SMRG model was developed using the real gas law and was satisfactorily applied for the microscopic investigation of the hexahelicene isotherms indicating that the lateral interactions between the adsorbates are responsible of the decrease of the adsorbed quantity at saturation. The interpretation of the two models’ parameters indicated that the adsorption of the two helicenes is an endothermic phenomenon. Interestingly, the heptahelicene is recommended for silver complexation because it shows the highest adsorption energies involving chemical bonds during the complexation process. The SMPG model and the SMRG model also allow prediction of three thermodynamic functions (configurational entropy, Gibbs free enthalpy, and internal energy) which govern the adsorption mechanism of silver on the two helicenes.

Calculation of adsorption isotherms by statistical physics models: a review

“…Another approximation is to ignore the rotational, vibrational, electronic, and nuclear degrees of freedom. Indeed, for a mono-atomic adsorbate, there are no vibrational and rotational degrees of freedom (Souissi and Ben Yahia 2021) and are frozen in a liquid medium (Alyousef et al 2020c). If the electronic and nuclear energy levels of the adsorbate are higher, the corresponding freedoms cannot be thermally excited (Yahia et al 2017b).…”

“…If the electronic and nuclear energy levels of the adsorbate are higher, the corresponding freedoms cannot be thermally excited (Yahia et al 2017b). Only the translation degree of freedom can be taken into account because it can be excited at the surrounding temperature (Marwa et al 2016;Souissi and Ben Yahia 2021;Yahia et al 2017b). On the other hand, it is considered that a unit mass of solid phase contains N M adsorption sites, and each site, characterized by its energy -ε, can adsorb a variable number of adsorbate species (Selim et al 2019b).…”

“…Some studies highlighted the impact of temperature on the evolution of the values of the Van der Waals parameters. Souissi et al (Souissi and Ben Yahia 2021) noticed that the interaction between the particles of the adsorbate is weak at high temperatures (decrease in the values of the parameter "a"). Furthermore, increasing the value of the parameter "b" suggested that increasing the temperature promoted repulsion between silver ions.…”