Polydopamine-Coated Waste Cardboard Roll Evaporator for High-Performance Solar Desalination

Abstract

: Global freshwater scarcity has stimulated increasing interest in solar-driven interfacial evaporation for decentralized water purification. However, the development of low-cost evaporators that simultaneously achieve efficient photothermal conversion, continuous water supply, and functional separation of light harvesting and water transport remains a major challenge. Herein, we report a waste-cardboard-derived Janus cylindrical evaporator that integrates spatially separated photothermal conversion and water transport functions through a simple edge-immersion polydopamine (PDA) coating strategy followed by a rolling process. The PDA-coated upper region serves as a broad-band light absorber with a solar absorption exceeding 95% across 250–2500 nm and exhibits hydrophilicity, while the uncoated lower region retains the natural capillary network of cellulose fibers for continuous water supply. Under one-sun illumination, the evaporator delivers an evaporation rate of 2.07 kg m − 2 h − 1 with a photothermal conversion efficiency of 88.1%. In practical tests, it achieves over 99.9% rejection of primary ions (Na + , Mg 2+ , K + , Ca 2+ ) and removes organic dyes with efficiencies exceeding 99%. This work presents a sustainable “waste-to-clean-water” strategy that valorizes discarded cardboard, offering a promising pathway toward decentralized and low-cost solar water purification.