• • Under 1 sun, the PNMF evaporator delivers 2.71 kg m−2 h−1 with ~90% solar-thermal conversion efficiency sustained over 24 cycles; this rate exceeds conventional hydrophilic melamine foam (PMF) which fails via salt crystallization within 1 h in seawater, directly enabling continuous operation without frequent maintenance.
• • In 10 wt% NaCl simulated seawater, no NaCl crystals appear on the PNMF surface after 12 h, and the evaporation rate remains stable at 2.62–2.87 kg m−2 h−1 over a 20-day period; this salt resistance eliminates the need for periodic washing or brine discharge, reducing operational downtime and labor costs in remote or offshore installations.
• • Under natural autumn sunlight (average irradiation <0.4 kW m−2, temperatures <24 °C), a portable PNMF-based device achieves a maximum hourly evaporation rate of 0.52 kg m−2 h−1 and cumulative freshwater production of ~3 kg m−2 over 11 h, with purified water salinity below 0.14‰; this demonstrates reliable performance under low-intensity, cool conditions where many high-efficiency evaporators underperform.
• • The sandwich wettability design—hydrophobic top, hydrophilic middle, tunable hydrophobic bottom—enables directional water transport and Marangoni-driven salt backflow, preventing accumulation on the evaporation surface; this structural mechanism, combined with self-floatability from hydrophobic edges, minimizes heat loss and ensures long-term durability without complex auxiliary systems.