A Picosecond Laser-Processed Gradient-Distributed Fe3O4@PDMS Evaporator for Efficient Seawater Desalination

Solar-driven interfacial steam generation technology is regarded as an effective method for freshwater production. Nevertheless, conventional evaporators suffer from weak light absorption and a trade-off between high evaporation rate and salt resistance, which restricts their practical applications. Herein, we developed a picosecond laser-modified gradient Fe3O4@polydimethylsiloxane (LG-Fe3O4@PDMS) interfacial evaporator fabricated via layered curing combined with laser processing. This evaporator features a gradient composition along its thickness direction. The upper layer with a high Fe3O4 content serves as the photothermal conversion layer, while the underlying PDMS substrate suppresses heat conduction toward the bulk water at the bottom. The periodic grooved arrays on the surface enhance light harvesting via multiple light reflections and scattering and simultaneously enable the enrichment of Fe3O4 particles on the evaporation surface. The LG-Fe3O4@PDMS exhibits a light absorptivity of nearly 98% across the full solar spectrum of 250-2500 nm, accompanied by outstanding photothermal temperature rise performance and hydrophobicity. Under 1 sun illumination (1 kW m-2), the evaporation rate reaches 2.79 kg m-2 h-1. In addition, the material retains 72.4% of its original evaporation performance even in a 25 wt % high-salinity solution. Seven-cycle stability tests verify its outstanding resistance to salt crystallization. The design concept of this gradient composite structure offers a simple and feasible strategy for fabricating high-performance and long-term stable interfacial evaporators, as well as for practical applications in seawater desalination and organic wastewater purification.