Kinetics, Isotherm, and Thermodynamic Studies of the Adsorption Mechanism of PFOS and PFOA Using Inactivated and Chemica
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Kinetics, Isotherm, and Thermodynamic Studies of the Adsorption Mechanism of PFOS and PFOA Using Inactivated and Chemically Activated Maize Tassel Patricia N. Omo-Okoro & Christopher J. Curtis & Pavlína Karásková & Lisa Melymuk & Opeyemi A. Oyewo & Jonathan O. Okonkwo
Received: 10 June 2020 / Accepted: 27 August 2020 # Springer Nature Switzerland AG 2020
Abstract The extreme persistence, bioaccumulative, and toxicity tendencies of per- and polyfluoroalkyl substances (PFAS) have contributed to the ever-increasing quest for effective and low-cost technologies for removing PFAS from aqueous solutions. Therefore, in the
Highlights • Electrostatic attraction is highly involved in the adsorption of PFOS and PFOA. • Hydrophobic interactions play a significant role in the adsorption of PFOS and PFOA. • Maximum adsorption capacities were observed when the Freundlich model was applied. • The applied materials are promising adsorbents for PFAS removal from water systems. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11270-020-04852-z) contains supplementary material, which is available to authorized users. P. N. Omo-Okoro : C. J. Curtis Department of Geography, Environmental Management and Energy Studies (GEMES), Faculty of Science, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa P. N. Omo-Okoro : J. O. Okonkwo (*) Department of Environmental, Water & Earth Sciences, Faculty of Science, Tshwane University of Technology, Arcadia Campus, Private Bag X680, Pretoria 0001, South Africa e-mail: [email protected] P. Karásková : L. Melymuk RECETOX, Masaryk University, 625 00 Brno, Czech Republic O. A. Oyewo Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria 0001, South Africa
present study, maize tassel (MT) was activated using phosphoric acid. The chemically activated maize tassel (CAMT) was thereafter applied as an adsorbent for removing perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) from aqueous media in comparison with the inactivated MT. The adsorption behaviors of PFOS and PFOA onto MT and CAMT were investigated via adsorption experiments. It was found that the isothermal data fit better with the Freundlich isotherm model than with the Langmuir isotherm model. Maximum adsorption capacities of 1552.5 mg g−1 (3.10 mmol g−1) and 380.32 mg g−1 (0.92 mmol g−1) were recorded for PFOS and PFOA, respectively, using CAMT, when the Freundlich model was applied. Equilibrium was attained within 60 min using both MT and CAMT. The pseudo-second-order kinetics model suited the kinetics data better. It was observed from the thermodynamic studies that the adsorption mechanism of PFOS and PFOA on MT and CAMT is spontaneous and feasible. All the values for the Gibb’s free energy change (ΔG0, kJ mol−1) obtained in the present study were below − 20 kJ mol−1. The adsorption of PFOS and PFOA using CAMT is exothermic in nature (enthalpy, ΔH0 was negative) whereas the adsorption of PFOS and PFOA using
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