Kinetic and Mechanism Study of PFOS Removal by Microscale Zero-Valent Iron from Water

This study compares the removal of perfluorooctanesulfonic acid (PFOS, C₈F₁₇SO₃H) by microscale zero-valent iron (mZVI) and activated carbon (AC) and investigates the contribution of both the magnetic and nonmagnetic portions of reacted mZVI to the removal of PFOS. Results showed that the mZVI had a significantly higher areal adsorption capacity (21 mg/m²) compared to AC (0.813 mg/m²). 10 g/L of mZVI at neutral pH reduced PFOS concentrations from 50 to 6 mg/L within 8 h. Magnetic solids showed a removal capacity significantly higher than those of iron oxides and hydroxides. Low F^- concentration (∼1 mg/L) suggested that defluorination was not the main removal mechanism. Acid-washed mZVI showed only minor improvements in removal efficiency, indicating the iron oxide layer does not significantly affect PFOS adsorption. The in situ ATR-FTIR spectra revealed that the removal of PFOS by mZVI was not due to the formation of covalent bonds between PFOS and mZVI. The negatively charged mZVI significantly removed PFOS anions at pH > 7, indicating that the removal mechanism was not due to the electrostatic attraction. Furthermore, the presence of NaCl enhanced PFOS removal, proving the hydrophobic effect as a key mechanism. The results of this study will benefit the development of a high specific surface area mZVI for treating PFOS.