Synergistic PEDOT:PSS/Fe-Mn Oxide Functional Coating on PVDF Membrane for Enhanced Arsenate Removal: Surface Properties, Interfacial Adsorption Behavior, and Ligand Exchange Mechanism

In this study, a functional surface coating composed of Fe-Mn binary oxide (FM) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, PP) was applied to a PVDF membrane (PP-FM-PVDF) for efficient arsenate (As(V)) removal. PP acts as a dispersant and hydrophilic modifier, ensuring uniform FM distribution and reducing the water contact angle to 50.1°. The PP-FM-PVDF membrane achieves a maximum As(V) adsorption capacity of 30.43 mg/g, outperforming pristine and singly modified membranes. The batch adsorption data fit the Langmuir isotherm (R2 = 0.999) and pseudo-second-order kinetic model (R2 = 0.99), indicating monolayer chemisorption. The coating increases the specific surface area to 27.33 m2/g and the tensile strength to 6.41 MPa. Dynamic filtration shows that 2.70 L (2149.7 L/m2) of 100 μg/L As(V) solution can be treated before the permeate concentration exceeds the WHO guideline of 10 μg/L. After alkaline regeneration (pH 11), 62.9% of the initial capacity is retained. Complementary surface-sensitive analyses (zeta potential, XPS, and EXAFS) reveal that arsenate adsorption occurs primarily through ligand exchange between arsenate oxyanions and Fe/Mn surface hydroxyl groups on the coating, forming inner-sphere bidentate complexes (Fe–O–As and Mn–O–As), while electrostatic interactions play a secondary, pH-dependent role. This surface engineering strategy—synergistically integrating a conductive hydrophilic polymer with a metal oxide as a functional coating on PVDF—offers a reusable, high-performance platform for arsenate remediation, underscoring the critical role of interface design in environmental membrane applications.