Crosslinking-controlled interfacial water-state regulation in a hierarchical PDA@Fe3O4/PVA hydrogel for accelerated solar evaporation

Interfacial water states are regulated by PDA@Fe 3 O 4 -crosslinked PVA. • Heat localization and mass transport are balanced via triple-layer hydrogels. • Optimized H-bond relaxation kinetics are revealed by spectroscopy and MD. • Hypersaline wastewater treatment is achieved by the robust system. Solar-driven interfacial evaporation (SIE) holds immense potential for decentralized clean water production, yet intrinsic transport bottlenecks and high kinetic barriers of vaporization often limit its practical outputs. Here, we present a functionally graded triple-layer evaporator designed through interfacial barrier engineering to decouple heat localization from mass transport. By constructing a hydration-regulated gradient—comprising a photothermal PDA@Fe 3 O 4 top-layer, a crosslinking-tuned intermediate hydrogel, and a macroporous scaffold—we demonstrate precise control over water states. Crucially, our results suggest that the evaporation enhancement is more closely associated with interfacial water-state regulation and hydrogen-bond relaxation behavior than with a simple ‘enthalpy reduction’ interpretation, as consistently supported by the combined spectroscopic observations and molecular dynamics analysis. This gradient architecture enables an evaporation rate of 3.10 kg m −2  h −1 with approximately 92% efficiency under one-sun. Our work provides a mechanistic framework for overcoming the transport-energetics trade-off in SIE, offering a robust solution for treating diverse hypersaline and complex wastewater.