Modeling of heavy metal ion adsorption isotherms onto metallophthalocyanine film

Tetrakis [bis(pentafluorophenyl)methoxy]phthalocyaninato zinc(II) (4) coated quartz crystal microbalance (QCM) sensor was developed to detect the heavy metal ions in aqueous solution. The results of the sensor test experiments show that compound 4 is powerful sensing layers capable of working also in the liquid phase to detect heavy metal ions. The equilibrium sorption data were fitted into Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Jovanovic isotherms. The rate constants, equilibrium capacities and related correlation coefficients for each isotherm model were calculated and discussed. Regression analysis showed that the Langmuir isotherm model was the most appropriate for fitting the experimental data for Cu²⁺ ions. The maximum monolayer coverage from Langmuir isotherm model was determined to be 1.64 × 10⁴ mg/g. The obtained values of the separation factor indicating a favourable sorption. On the other hand, it was observed that there is an accessible competition between Freundlich and Langmuir models for the sorption of Co²⁺ ions onto the sensing layer. Results also show that the linear regression analysis with respect to Jovanovic isotherms generates a straightline that best fit to the data of sorption of Fe²⁺, Mg²⁺ and Zn²⁺ ions.