To address the challenge of efficient antimony [Sb(III)] removal from wastewater, we developed a hierarchically structured β-FeOOH@PDA/PEI-PTFE composite membrane that combines synergistic adsorption and photocatalytic functions. A conformal PDA/PEI layer was deposited on PTFE membranes to promote Fe3+ chelation and support the in situ growth of vertically aligned β-FeOOH nanorods. Multiscale characterization (SEM, EDS, ATR-FTIR, XRD, and XPS) confirmed uniform β-FeOOH distribution, covalent Fe–O–C bonding, and the presence of functional groups (−NH2, Fe–OH), which are critical for Sb(III) uptake. The membrane demonstrated excellent adsorption performance, achieving 95% removal at pH 7, with a capacity of 420.01 mg/m2 and 5 mg/L Sb(III). Adsorption kinetics and isotherms followed pseudo-second-order and Freundlich models, indicating heterogeneous multilayer chemisorption. The presence of competitive ions (e.g., HPO42–, CO32–) had minimal impact, highlighting the membrane’s selectivity. Under UV irradiation, photocatalytic oxidation further increased Sb(III) removal to 98% within 60 min through •OH/h+-mediated oxidation to Sb(V), supported by Fe3+/Fe2+ redox cycling, as confirmed by XPS and ESR analyses. The PDA/PEI matrix enhanced structural stability via π–π conjugation and hydrogen bonding, allowing the membrane to retain 76.3% of its efficiency after five regeneration cycles, despite minor photocorrosion and pore blockage. This study reveals a dual-functional mechanism involving electrostatic attraction, complexation, and photocatalysis, offering a sustainable and scalable strategy for antimony remediation in complex water environments.