Breath figure-derived Janus membrane with CCM/PNIPAM hydrogel layer for highly efficient salt-tolerant evaporation

Using the green BF method instead of traditional membrane pore-forming technology • The Janus structure provides optimized water transport and light absorption. • CCPN-PPM delivers an evaporation rate of 1.87 kg m −2  h −1 , 97.7% efficiency. • Resistant to high salt content (20 wt% NaCl) and grease (diesel, motor oil). Solar-driven interfacial evaporation (SDIE) is one of the key technological approaches for alleviating global freshwater shortages. In this study, a porous substrate membrane (PPM) was prepared using the green breath figure (BF) method and combined with a poly(N-isopropylacrylamide) (PNIPAM) hydrogel doped with hollow conjugated microporous carbon microspheres (CCM), successfully constructing a composite photothermal membrane (CCPN-PPM) with Janus wetting properties, designed to yield an evaporator material with both excellent salt resistance and oil repellency. The hollow cavity structure of the CCM significantly enhances light absorption. The PNIPAM hydrogel provides hydrophilic water transport channels and temperature-sensitive self-regulation capabilities, while the underlying BF membrane ensures rapid vapor escape. Experiments demonstrate that CCPN-PPM exhibits an average light absorption rate of up to 97.5% across the 250–2500 nm wavelength range. At an irradiance of 1 kW m −2 , its evaporation rate reaches 1.87 kg m −2  h −1 , with a photothermal conversion efficiency of 97.7%. In an 11-hour continuous day-night alternating evaporation test in simulated seawater, the material maintained stable seawater evaporation performance and exhibited an evaporation capacity comparable to that in pure water under varying light intensities. It achieved a salt-tolerant evaporation rate of 1.62 kg m −2  h −1 even in a high-salt solution containing 20 wt% NaCl. Furthermore, CCPN-PPM has demonstrated a certain degree of pollution control capability when treating dye wastewater, oil-containing dye wastewater, and difficult-to-treat oil contaminants such as diesel and engine oil. This work extends the advantages of the BF in the preparation of functionalized evaporators and provides new material design concepts for treating complex wastewater containing salt and oils. Download: Download high-res image (133KB) Download: Download full-size image