A self-regenerating air-laid paper wrapped ASA 3D cone-shaped Janus evaporator for efficient and stable solar desalination

Solar desalination is one of the most sustainable and effective techniques to solve the long-standing challenge of fresh water supply. However, most of the current solar evaporators are designed with the light absorbing surface in parallel with the water evaporating surface, which causes significant salt accumulation and stability issues. Herein, a facile but scalable approach is reported to build tree-inspired, cone-shaped 3D Janus evaporators by spatially isolating absorption surface and evaporation surface, which exhibit self-regenerating behavior and significantly extended durability. Such evaporators employ hydrophobic polymer-based inner cones as the light absorbing surface, which were fabricated via 3D printing and featured wavelike and porous surface texture, that provides remarkable solar harvesting and fast thermal response. The outer surface of the cone was wrapped with superabsorbent air-laid paper, which not only provides efficient water supply featuring a bottom-up thickness gradient for evaporation but also avoids salt accumulation directly on the evaporation surface. Overall, the rational structure design and material combination enable the evaporator feature excellent heat-localization, efficient interfacial evaporation and remarkable long-term stability. It exhibited a stable evaporation rate of 1.713 kg m–2 h−1 for 14 days to 3.5% artificial seawater (solar/dark conditions for 9/15 h per day), without measurable decay. Most importantly, both experiments and COMSOL Multiphysics calculations reveal that the evaporator could also gain extra heat from surroundings. This work could provide new insights on the design of practical devices for effective water purification to address the critical water shortages challenges.