Enhanced As(V) removal by a Zr-doped β-FeOOH functionalized PTFE membrane: Interfacial structure, selectivity, and ligand exchange

Arsenic (As) contamination poses a critical threat to water safety, yet efficient removal of As(V) remains challenging due to the lack of robust adsorbents with high selectivity and stability. Herein, a Zr-doped β-FeOOH-functionalized PTFE membrane (Zr/β-FeOOH-PDA/PEI-M) has been reported and fabricated via in situ mineralization on a PDA/PEI interlayer. By optimizing the Fe-to-Zr molar ratio to 3:2, an unprecedented balance between abundant Zr-O active sites and the preservation of β-FeOOH lattice integrity was achieved, as evidenced by multi-scale characterization. The optimized membrane delivers a remarkable As(V) removal efficiency of 97% with an adsorption capacity (Q_e) of 442.01 mg/m² in cross-flow filtration, outperforming most state-of-the-art materials. Notably, it exhibits exceptional tolerance to coexisting ions (Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, CO₃^2-, PO₄^3-) and natural organic matter, maintaining > 80% removal in real Pearl River water and meeting discharge standards. Mechanistically, we reveal a diffusion-ligand exchange-inner-sphere complexation pathway in which Zr⁴⁺ enhances Lewis acidity and coordination affinity, while Fe-O sites play an auxiliary role, collectively accounting for the superior selectivity. This work not only provides a scalable, high-performance membrane for As(V) remediation but also offers insights into the rational design of Zr-based adsorbents for capturing toxic oxyanions.