Breaking the trade-off between hydration and stability: an interface-locked, non-swelling zwitterionic hydrogel membrane for durable oil/water separation

Hofmeister effect induces a dense network with <10% swelling ratio over 7 days. • In-situ SnO 2 growth and PDA anchoring prevent hydrogel coating delamination. • High flux (∼2323 L m −2 h −1 bar −1 ) and >99.3% efficiency for O/W emulsions. • Superior durability against fouling, hydraulic shear, and harsh chemicals. Hydrogel-functionalized membranes hold immense promise for the purification of oily wastewater but are persistently plagued by the intrinsic trade-off between hydration capacity and structural stability—specifically, excessive swelling and interfacial delamination. Herein, a robust, interface-locked zwitterionic hydrogel composite membrane (SPSPM) is engineered to defy these limitations for sustainable, high-performance oil/water separation. The strategy involves the in-situ growth of SnO 2 nanoparticles on a stainless-steel mesh to create a hierarchical micro/nanostructured foundation, followed by polydopamine anchoring to ensure robust interfacial adhesion. Crucially, a zwitterionic PSBMA/polyvinyl alcohol hydrogel coating is constructed via a Hofmeister effect-induced salting-out strategy. This approach synergistically promotes dense physical crosslinking and polymer chain crystallization, endowing the hydrogel with exceptional anti-swelling resistance (swelling ratio < 10% over 7 days) and high mechanical toughness. The resulting membrane exhibits superior superhydrophilicity and underwater superoleophobicity, achieving great separation efficiency (>99.3%) and high permeation flux (∼2323 L m −2 h −1 bar −1 ) for diverse surfactant-stabilized emulsions. Moreover, the SPSPM demonstrates remarkable long-term stability against dynamic hydraulic shear, chemical corrosion (acid/alkali/salt), and irreversible fouling, maintaining >96% flux recovery over extended cycles. This work presents a facile and effective strategy to resolve the swelling and delamination issues of hydrogel membranes, providing a reliable material for durable oily wastewater treatment. Download: Download high-res image (203KB) Download: Download full-size image