Fabrication of a facile self-floating lignin-based carbon Janus evaporators for efficient and stable solar desalination

Desalination with solar-driven photothermal evaporator is extremely attractive for tackling the current freshwater shortage of humanity, and a scalable and efficient interfacial solar evaporator is thus highly desirable. In this work, a facile low-cost Janus evaporator with excellent evaporation performance and energy conversion performance was fabricated from potassium hydroxide (KOH)–activated lignin-based carbon (KLC) and commercial melamine foam (MF). The KLC with rich and multiple microscale/nanoscale pores presented high light absorption (90%) and excellent photothermal conversion capacity (up to 60.4 °C) in the full solar spectrum (200–2500 nm). Subsequently, the KLC was simply coated on the upper surface of MF to obtain the self-floating Janus KLC/MF evaporator. The hydrophilic nature and the porous structure of MF ensured sufficient water supply to the evaporation interface and facilitated effective diffusion of water vapor. The solar steam generation test revealed that the water evaporation rate of the Janus KLC/MF under simulated sunlight was 1.539 kg m⁻² h⁻¹, with a superior photothermal conversion efficiency of 95.88%, which is higher than previously reported melamine-framed evaporators. Moreover, the evaporator has an excellent recycling ability and shows a stable water evaporation rate, indicating preferable durability in practical desalination. Overall, this work demonstrates the great potential of using low-cost lignin as a feedstock for the preparation of solar-driven interfacial evaporation systems integrating multiple functionalities for clean water production and thus offers a viable strategy for the application of lignin-based functional materials.