Renewable β-FeOOH nanorods modified polyvinylidene fluoride membrane enables high potable water quality: Performance and mechanisms

Abstract

To overcome conventional membrane challenges in eliminating natural organic matter (NOM) from natural water, we successfully integrated β-iron hydroxide oxide (β-FeOOH) nanorods onto a PAA-PVDF blend membrane fabricated from poly(acrylic acid) (PAA) and polyvinylidene fluoride (PVDF).Contact angle assessments with various fluids confirmed the strong organic matter adsorption property of the membrane, with a dispersion component of surface energy at 26.7 mJ/m² for β-FeOOH@PAA-PVDF. This membrane consistently removed over 80 % of dissolved organic matter in the cross-flow filtration of water containing 50–150 ppm fulvic acid (FA) under neutral conditions. Such remarkable performance is attributed to the interactions between the Fe-OH groups and the carbonyl (2.960 eV) and phenolic (2.864 eV) groups of FA, overcoming the size sieving limits. Under acidic conditions, zeta potential tests revealed effective ferric coagulation, resulting in over 90 % FA (50 ppm) removal. We thoroughly investigated that common cations (e.g., K⁺ and Ca²⁺) have impacts on FA removal using β-FeOOH@PAA-PVDF. The used membranes regained nearly original fluxes after washing with trace hydrogen peroxide (H₂O₂) under ultraviolet (UV) light illumination, outperforming traditional washing with sodium hypochlorite (NaClO). Electron spin resonance spectrometry elucidated the cleaning mechanism of β-FeOOH@PAA-PVDF was superoxide anion radical (O₂⁻) and singlet oxygen (¹O₂) active species. In summary, β-FeOOH@PAA-PVDF showed a superior adsorption capacity (2200 mg/m²) and efficient photocatalytic degradation towards NOM in natural water, providing an efficient cleaning technology for membrane reuse.