Rapid and Reversible Capture of PFOS from Complex Water Matrices by an Earth-Abundant Iron(III)-Carboxylate...

Perfluorooctane sulfonate (PFOS) is a globally recognised persistent, bioaccumulative and toxic pollutant. Under China GB 5749-2022 and the US EPA 2024 drinking water MCL, permissible levels have fallen to 40 ng L^-1 and 4 ng L^-1, respectively, placing unprecedented demands on remediation technologies.

An iron(III)-carboxylate metal-organic framework prepared from low-cost precursors (denoted MOF-LC, [Fe₃O(BDC)₃Cl]·x(solvent)) was synthesised via a one-pot solvothermal route from FeCl₃·6H₂O and terephthalic acid (H₂BDC). The material was characterised by PXRD, N₂ adsorption, FTIR, TGA, XPS, elemental analysis and ICP-OES. Adsorption performance was evaluated under varying initial concentrations, contact times, pH values, coexisting inorganic anions (Cl^-, NO₃^-, SO₄^2-, HCO₃^-, PO₄^3-) and humic acid backgrounds, and by a panel of six water matrices.

MOF-LC exhibited a BET surface area of 1528 m² g^-1 and a dominant pore centred at 1.9 nm, which is geometrically compatible with the 1.36 nm molecular length of PFOS. Adsorption reached ≈95% of equilibrium capacity within 30 min and was best described by the pseudo-second-order model (R² = 0.998). Measured uptake reached 800.6 mg g^-1 at 298 K, corresponding to a Langmuir maximum capacity of 802 mg g^-1 (note that all adsorption experiments were conducted at mg L^-1 concentrations, several orders of magnitude above the regulatory limits cited above). Removal exceeded 88% across all six water matrices. PFOS removal efficiency fell from 99.2% to 85.8% over seven adsorption-regeneration cycles using a 1% NH₄Cl/methanol eluent, with 90.6% of the initial BET surface area retained and Fe leaching below 45 µg L^-1.

Electrostatic, hydrophobic and pore confinement contributions are proposed as cooperative interpretations consistent with the observations. MOF-LC is identified as a technically promising laboratory-scale sorbent for PFOS removal from complex water matrices. Performance at environmentally relevant ng L^-1 concentrations and economic viability at scale remain to be established.