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Activated carbons from banana peels for the removal of nickel ions

Bibaj, E., Lysigaki, K., Nolan, J. W., Seyedsalehi, M., Deliyanni, E. A., Mitropoulos, A. C., Kyzas, G. Z.
International journal of environmental science and technology 2019 v.16 no.2 pp. 667-680
Gibbs free energy, activated carbon, adsorption, banana peels, enthalpy, entropy, equations, hot water treatment, ions, models, nickel, pH, phosphoric acid, pollutants, pyrolysis, scanning electron microscopy, surface area, temperature
This work aims the study of two types of activated carbons, produced with hydrothermal treatment (BAC-H samples) and pyrolysis (BAC-P samples) using from banana peels as source. The activation was done with H₃PO₄ (at three different temperatures 400, 500, 600 °C) in order to examine the effect of this time differentiation. The samples prepared a brief characterization which was also presented observing the morphology of the carbon samples with SEM images and their specific surface area (BET analysis). The adsorption ability of the prepared activated carbons was extensively evaluated using as model pollutant nickel ions. Adsorption experiments were realized to evaluate the optimum solution pH (6). Detailed equilibrium analysis was done running three isotherm models for the fitting of equilibrium data (Langmuir, Freundlich and Langmuir–Freundlich equations). The equilibrium data were repeated similarly at four different temperatures (20, 30, 40, 50 °C) in order to result the respective thermodynamic evaluation of this system. Generally, the adsorption capacity of pyrolized carbons was higher than that of hydrothermal ones; this slight difference may be attributed to the different surface area (slightly higher of pyrolized 415–488 m²/g than of hydrothermal 315–320 m²/g). Furthermore, in the pyrolized carbons, the increase in temperature drastically improved (30%) the Qₘₐₓ of BAC400-P from 229 (20 °C) to 299 (50 °C). Based on the fact that four different temperatures were examined in equilibrium, the respective thermodynamic analysis was done in order to export some very important parameters as enthalpy, entropy and free energy for the system (ΔH°, ΔG°, ΔS°).