Surface Roughness Engineering for High-Salt-Tolerant Solar Evaporator with Enhanced Efficiency in Sustainable Desalination

Graphical A 3D column-shaped evaporator is introduced to construct spatially separated crystallization sites by KAC coating, which effectively prevents the connections of salt crystals. This coating creates a rough surface with abundant KAC protrusions, achieving an evaporation rate of 8.18 kg m −2 h −1 for a 15 wt% NaCl solution under 1 kW m −2 solar radiation. The accumulation of dense crystal layers on solar evaporators compromises the performances by reducing light absorption efficiency and obstructing water transport channels, ultimately diminishing evaporation rate. To mitigate this issue, spatially separated crystallization sites can be engineered on the evaporator surface to disrupt salt adhesion and prevent dense layers formation. In this study, a 3D column-shaped wood evaporator (KOH-activated carbon- delignified wood (KAC-DW)) is developed by coating DW with KAC. The KAC coating creates microstructured surface featuring abundant protrusions (≈144 mm −2 , each 20 μm in height), which effectively inhibit salt crystal adhesion. Under 1 kW m −2 solar radiation with a 15 wt% NaCl solution, the KAC-DW evaporator achieves an impressive water evaporation rate of 8.18 kg m −2 h −1 over 96 h (0 m s −1 wind speed)—more than double the performance of uncoated DW (3.91 kg m −2 h −1 ). This enhancement stems from two key mechanisms: 1) the KAC protrusions prevent dense crystal layer formation, preserving open surface channels for evaporation, and 2) they promote the growth of loose salt crystals, thereby expanding the effective evaporation area and further boosting the evaporation rate.