A self-descaling Janus nanofibrous evaporator enabled by a "moving interface" for durable solar-driven desalination of hypersaline water

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2022-10, Vol.1 (39), p.2856-2865
• Main Authors: Li, Hao-Nan, Yang, Hao-Cheng, Zhu, Cheng-Ye, Wu, Jian, Greiner, Andreas, Xu, Zhi-Kang
• Format: Article
• Language: English
• Subjects: Accumulation; Desalination; Descaling; Evaporation; Evaporation rate; Evaporators; Hydrophilicity; Iron oxides; Night; Photothermal conversion; Poly(N-isopropylacrylamide); Polyacrylonitrile; Polyisopropyl acrylamide; Sodium chloride; Steam generation; Sunlight; Wettability
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta05555d

Solar-driven desalination by using porous evaporators has been deemed to be a sustainable pathway to obtain freshwater. Despite the emerging anti-scaling evaporators, the durable evaporation in hypersaline water remains a formidable challenge because of the unpreventable salt accumulation in the porous structures. To enhance the descaling capacity of evaporators, a self-descaling Janus evaporator (SJE) featuring a "moving interface" is developed for durable and efficient desalination of hypersaline water. This evaporator consists of an Fe 3 O 4 -embedded poly( N -isopropylacrylamide) (PNIPAM) nanofibrous layer and a hydrophilic polyacrylonitrile (PAN) nanofibrous layer constrcuted by sequential electrospinning. Integrating the photothermal conversion of Fe 3 O 4 and the thermal responsiveness of PNIPAM, the SJE exhibits a reversible solar-induced wettability transition from asymmetric wettability (under sunlight) to hydrophilic wettability (at night). Under sunlight, the top surface and the evaporation interface ( i.e. air-water interface) are separated to prevent salt accumulation on the evaporator, benefiting efficient solar steam generation. At night, the air-water interface moves to the upper surface, showing the self-descaling ability. With this design, the SJE exhibits a high-efficiency water evaporation rate of 1.76 kg m −2 h −1 under one sun and demonstrates long-term stability (over 5 days) when treating 20 wt% NaCl solution. Overall, this work provides an exciting material solution with photothermal responsive design for the practical application of Janus evaporators in brine desalination. A Janus evaporator featuring a "moving interface" is developed. The photothermal layer shows a reversible wettability transition from the daytime to the night, performing excellent de-scaling capacity when treating hypersaline feed.