Adsorption behavior of [meso-tetrakis(4-carboxylatophenyl)porphyrinato]oxovanadium(IV) tetrasodium in aqueous solution onto chitosan

The adsorption behavior of [meso-tetrakis(4-carboxylatophenyl)porphyrinato]oxovanadium(IV) tetrasodium, [VO(tcpp)]Na₄, in aqueous solution onto chitosan 7B has been investigated. The factors affecting the sorption process such as solution pH, initial concentration of [VO(tcpp)]Na₄ solution and temperature were determined in batch mode. Adsorption kinetic data obtained from different batch experiments was tested using pseudo first-, second-order, Elovich, intraparticle, and film diffusion kinetic models. Langmuir, Temkin, and Freundlich isotherm models were used for the description of equilibrium adsorption data. The best results were achieved with the pseudo second-order kinetic and Freundlich isotherm equilibrium models, respectively. The film diffusion and intraparticle diffusion were the rate-limiting steps. The equilibrium adsorption capacity (q _e) increased with increasing the initial concentration of [VO(tcpps)]Na₄ solution, showing maximum adsorption capacity of 69.35 μmol/g. The activation energy (E _a) of sorption kinetics was estimated to be 46.21 kJ/mol in the temperature range 25–40 °C. Thermodynamic parameters such as changes in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were also evaluated by applying the Van’t Hoff equation. The values of thermodynamic parameters for [VO(tcpp)]Na₄ adsorption onto chitosan 7B indicate that it was spontaneous and endothermic nature.