Modeling of adsorption isotherms of zinc nitrate on a thin layer of porphyrin

Abstract

Adsorption isotherms of zinc nitrate are achieved at four temperatures using Tetraphenylporphyrin (TPP) coated onto Quartz crystal used as biosensor. These isotherms are fitted by models established through statistical physics formalism. It is found that a multilayer model with two energies is able to give good approximation of the experimental data. In this model, six parameters affecting the adsorption process were introduced and interpreted. Such parameters are namely the number of ions per site, the density of receptor sites, the two energetic parameters and the numbers of layers. The modeling of experimental isotherms using statistical formalism shows a powerful method to explain and interpret the adsorption process at microscopic level. The Simulation results suggested that the zinc is anchored onto two receptor sites. The values of the adsorption energies are less than 30kJ/mol which indicate that this cation is physically adsorbed by the TPP.