Polyaniline-modified sea sand suppresses phase-change-driven microplastic transport via regenerable interfacial retention for long-term solar desalination

Solar interfacial evaporation (SIE) provides a low-carbon route for seawater desalination, but its nonequilibrium phase-change interface may facilitate microplastic transfer from seawater to condensate. To mitigate this water-quality risk, a low-cost, regenerable photothermal interface was constructed by modifying natural sea sand with polyaniline (PANI@SS). The PANI coating enhanced broadband solar absorption and promoted interfacial water activation, achieving an evaporation rate of 2.20 kg·m-2·h-1. Adsorption, spectroscopy, thermodynamic analysis, and molecular dynamics simulations showed that PANI converted the weak physical retention of pristine sea sand into stable interfacial anchoring, counteracting phase-change-driven microplastic transport. Reversible protonation/deprotonation enabled pH-regulated interfacial affinity, supporting facile regeneration and sustained antifouling performance. PANI@SS effectively retained seven representative microplastics with different structures and polarities, indicating broad applicability. In a 30-day outdoor test using natural seawater from the Yellow, Yangtze, and Pearl River estuaries, cumulative freshwater production exceeded 220 kg·m-2, while major ion concentrations met drinking-water guideline limits. Evaporation performance, microplastic retention, and material structure remained stable after repeated evaporation-regeneration cycles. This study reveals the competition between phase-change transport and interfacial retention as a key mechanism governing microplastic migration and product-water safety in SIE, providing a practical strategy for efficient, durable, and regenerable solar desalination.