Efficient extraction of U(Ⅵ) from uranium-containing wastewater over a wide pH range using sulfonate-rich electrode materials

Efficient uranium removal from acidic and pH-fluctuating wastewater remains challenging because conventional binding groups are prone to protonation and deactivation under acidic conditions, while competing electrochemical side reactions can decrease the efficiency of U(VI) reduction. Herein, a sulfonic acid-rich polypyrrole electrode, PPy-SO3H, was fabricated by covalently grafting 4,4'-diaminostilbene-2,2'-disulfonic acid (DSDA) onto carboxyl-functionalized polypyrrole (PPy-COOH). The introduced -SO3H/-SO3- groups possess extremely low pKa values and can maintain negatively charged binding sites over a wide pH range, thereby promoting uranyl enrichment and interfacial coordination. Compared with pristine PPy-COOH, PPy-SO3H exhibited markedly enhanced U(VI) removal performance, achieving an experimental equilibrium capacity of 579.4 mg g-1 and a Langmuir-fitted maximum capacity of 667.4 mg g-1 at pH 6. More importantly, PPy-SO3H consistently exhibited higher U(VI) removal capacities than pristine PPy-COOH across a broad initial pH range, demonstrating enhanced pH adaptability. Electrochemical analyses indicated that the sulfonate-rich interface facilitated uranyl-related cathodic reactions and could partially suppress hydrogen evolution under more negative polarization. Mechanistic characterizations and DFT calculations revealed that U(VI) removal proceeded through a coupled process involving sulfonate-assisted uranyl enrichment, coordination/ion exchange, electrochemical reduction and surface immobilization of uranium-containing species. In addition, PPy-SO3H showed favorable selectivity toward U(VI) in mixed-ion systems and retained 87.1% of its initial removal capacity after 10 cycles. This work provides a sulfonate-rich interface engineering strategy for designing efficient, selective and reusable electrode materials for uranium-containing wastewater remediation.