Janus membranes with dynamically reversible solar evaporation interfaces

Interfacial solar evaporation is an innovative technique that has attracted significant attention for its potential applications across a variety of fields. Traditional evaporators either apply the hydrophobic surface or the hydrophilic, exposed to solar irradiation. However, both situations result in the poor heat and mass transfer with the long-term operations, further lower down evaporation performance. Herein, Janus membranes (FePP) were designed with dynamically reversible solar evaporation interfaces; the top surface exhibited superhydrophobic exposed to solar irradiation while superhydrophilic in the dark environment. This property minimizes salt fouling by regulating salt deposition during evaporation cycles, while facilitating easy recovery during the hydrophilic state. The solar evaporation performance has improved with the average rate of 1.48 ± 0.05 kg m⁻²h⁻¹, 2.6 times more than the control group of water interface without FePP under one-sun irradiation. Furthermore, it demonstrated excellent stability and strong salt-resistance ability in the long-term desalination and highly saline water operation. Even outdoor field tests, FePP also showed strong solar evaporation and desalination performance exposed to the changing irradiation under the sun. This work further promotes the practical applications of the solar interfacial evaporators into the wastewater treatment, water desalination and purification, and energy production.