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Kinetics, Isotherm, and Thermodynamic Studies of the Adsorption Mechanism of PFOS and PFOA Using Inactivated and Chemically Activated Maize Tassel

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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 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 MT is endothermic. The PFOS and PFOA adsorption processes using both MT and CAMT were greatly influenced by electrostatic and hydrophobic interactions.

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Data Availability

Processed data that are significantly related to the present research showing the effect of adsorption dosage on the adsorption mechanism of PFAS using MT and CAMT as adsorbents and has been reviewed and stored in the Mendeley Data Repository. It is available at https://data.mendeley.com/datasets/ykb39rn322/1

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Acknowledgments

Part of this work was carried out with the support of the core facilities of the RECETOX research infrastructure (Czech Ministry of Education, Youth and Sports: LM2015051 and CZ.02.1.01/0.0/0.0/16_013/0001761). Many thanks to Mr. Petr Senk who assisted with HPLC-MS/MS analyses of samples.

Funding

Omo-Okoro PN is grateful to the Tshwane University of Technology for the funding granted towards her doctoral studies. She also appreciates support from INTERWASTE project that enabled her study visit to the Czech Republic, funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 734522.

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Correspondence to Jonathan O. Okonkwo.

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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.

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Omo-Okoro, P.N., Curtis, C.J., Karásková, P. et al. Kinetics, Isotherm, and Thermodynamic Studies of the Adsorption Mechanism of PFOS and PFOA Using Inactivated and Chemically Activated Maize Tassel. Water Air Soil Pollut 231, 485 (2020). https://doi.org/10.1007/s11270-020-04852-z

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  • DOI: https://doi.org/10.1007/s11270-020-04852-z

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