Kinetic, isotherm and thermodynamic studies of the adsorption of phenol and tyrosine onto apatitic tricalcium phosphate

The present study was conducted to evaluate the feasibility of apatitic tricalcium phosphate with a Ca/P ratio of 1.50 for the adsorption of phenol and tyrosine from aqueous solutions. The adsorbent was synthesized at room temperature using an aqueous double decomposition method and characterized through physicochemical methods. Batch adsorption studies were conducted as a function of contact time, initial adsorbate concentration, temperature, and pH. The adsorption kinetics of phenol and tyrosine were well fitted to the pseudo-second-order model. The maximum adsorption capacity was found to be 5.56 mg/g for phenol and 9.65 for tyrosine mg/g at 298 K. The adsorption of phenol and tyrosine was well explained using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevick models. The Langmuir model is the most suitable, with a maximum monolayer adsorption capacity of 7.32 mg/g for phenol and 11.43 mg/g for tyrosine at 298 K. The thermodynamic parameters indicate that the adsorption process is favorable, spontaneous, exothermic, and controlled by physisorption with electrostatic interactions between compounds containing the phenolic group and apatite. The results of this study have demonstrated the potential utility of apatitic tricalcium phosphate, which could be developed into a viable technology for the adsorption of compounds containing the phenolic group from aqueous solutions

The Removal of Phenol Through Adsorption onto Synthetic Calcium Phosphates – A Study Encompassing Analyses of Kinetics and Thermodynamics

The characteristics and suitability of hydroxyapatite (HAP), tricalcium apatite phosphate (PTCa), and octocalcium apatite phosphate (OCPa), which possess similar attributes to those of an ideal adsorbent, were investigated to determine their efficacy in phenol removal. The aim of this paper is to assess the adsorption behavior of phenol on phosphates powders synthesized by the co-precipitation method at ambient temperature. Furthermore, the impact of initial phenol quantities and thermal conditions on the adsorption process was explored. X-ray diffraction analysis revealed the formation of HAP, PTCa, and OCPa structures under room temperature conditions. The sample morphologies were subjected to scrutiny utilizing MEB together with X-ray analysis. Additionally, chemical analysis revealed that Ca/P = 1.6, 1.5, and 1.33 for HAP, PTCa, and OCPa, respectively. The synthesized powders exhibited adsorption abilities of 2.86, 2.74, and 2.52 mg/g for HAP, PTCa, and OCPa, respectively, and reached equilibrium in approximately 80 minutes. The study revealed that the experimental data are appropriately represented by the Langmuir and Freundlich adsorption equations for HAP and PTCa, and Langmuir model in the case of OCPa, as well as by the pseudo-first-order and pseudo-second-order adsorption kinetics. Thermodynamic evaluations, including calculations of ΔG°, ΔH°, and ΔS°, were performed. The results indicated that the adsorption mechanisms exhibited physical characteristics, were thermally absorbing in the case of HAP and exothermic for the other two phosphates, PTCa and OCPa, and occurred spontaneously