Adsorption of [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4–) onto chitosan in aqueous solution

Adsorption of [meso-tetrakis(4-sulfonatophenyl)porphyrinato]oxovanadate(IV)(4–), [VO(tpps)], onto chitosan 7B in aqueous solution was investigated in a batch system. The effects of solution pH, initial concentration of [VO(tpps)], and temperature were studied. Adsorption kinetic data obtained from different batch experiments was modeled using both pseudo first- and second-order kinetic equations. Freundlich, Tempkin, and Langmuir models were used for the description of adsorption equilibrium data. The best results were achieved with the pseudo second-order kinetic and Langmuir isotherm equilibrium models, respectively. The equilibrium adsorption capacity (q _e) increased with increasing the initial concentration of [VO(tpps)], showing maximum adsorption capacity of 441.21 μmol/g. The activation energy (E _a) of sorption kinetics was estimated to be 19.84 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 of [VO(tpps)] adsorption onto chitosan 7B indicate its spontaneous and endothermic nature. The present work provides a first example for the preparation of chitosan–[VO(tpps)] complex in aqueous solution.