Micronano Structured Polyimide Films Fabricated Using a Femtosecond Laser for Seawater Desalination

In the face of the global freshwater shortage crisis, solar-driven interfacial evaporation (SDIE) technology has emerged as a promising and sustainable solution. However, its practical application is constrained by severe salt accumulation and insufficient long-term evaporation stability. In this work, a polyimide (PI) photothermal film was prepared by femtosecond laser treatment technology, and coral-like micronanostructures were formed on the surface of the film to achieve efficient and stable desalination and wastewater purification. Due to the micronanostructures, hydrophilicity, and water transport channels on the surface, it exhibits a high light absorption rate (93%) and evaporation efficiency (67.3%). More importantly, this structure provides sufficient water for surface evaporation and prevents salt accumulation on the evaporator surface. Therefore, under one-sun irradiation, the evaporation rate can reach 2.94 kg m^–2 h^–1 in a 3.5 wt % NaCl solution. A stable average evaporation rate of 2.83 kg m^–2 h^–1 was achieved for 6 consecutive hours. In outdoor environments, a freshwater collection amount of 4.2 kg m^–2 per day can be obtained. This research provides a pathway for the development of stable and efficient freshwater acquisition technologies, demonstrating great application prospects in the fields of seawater desalination and wastewater treatment.