Three-dimensional freeze-casting solar evaporator for highly efficient water evaporation and high salinity desalination

The escalating global freshwater crisis demands sustainable water management strategies, such as solar-driven interfacial steam generation (SISG). Three-dimensional (3D) photothermal evaporators emerge as a promising solution due to significantly higher evaporation rates compared to two-dimensional (2D) counterparts. This study described the design and fabrication of M-shaped 3D evaporators using the freeze-casting technique with graphite nanopowder (GNP) and polyvinylidene fluoride (PVDF). Under 1.0 kW m−2 solar irradiation and 4 m s-1 convective flow, a high evaporation rate of up to 10.5 kg m−2 h−1 in pure water was achieved. The M-shaped 3D evaporators demonstrated excellent performance in solar desalination and wastewater treatment, maintaining stability even in a 20 wt% sodium chloride (NaCl) solution at 1.0 kW m−2 solar irradiation and 2 m s−1 convective flow, with a rate of approximately 3.8 kg m−2 h−1. These findings highlight the significant potential for leveraging the synergistic interplay between solar energy and convective flow, which can be harnessed through the fabrication of customized 3D evaporators via freeze-casting. This innovative approach offers a scalable and cost-effective solution, contributing to both efficient water evaporation and environmentally sustainable high salinity desalination for future water treatment.