Janus Wettability Grooved Structure for Convection-Enhanced Evaporation and Directional Salt Collection

Freshwater scarcity is a global challenge, and solar-driven interfacial evaporation (SDIE) technology has received widespread interest for its sustainability. However, vapor accumulation and salt deposition significantly reduce its performance. This study describes a solar evaporator with a Janus wettability grooved structure. This design not only allows for efficient double-sided evaporation but also provides a localized heat environment that greatly improves natural convection, effectively enhancing vapor diffusion. Under 1 sun irradiation, the optimized evaporator (JGE-60°) had an evaporation rate of 2.27 kg m^-2 h^-1. Under forced convection (4 m/s) conditions, its surface temperature dropped below ambient, reversing heat loss and increasing the evaporation rate to 5.96 kg m^-2 h^-1. Owing to the asymmetric wettability of its dual-sided structure, salt is selectively directed and deposited on the shaded side. This enables stable operation for 30 h in a 20 wt % brine while achieving a salt collection rate of 193.9 g m^-2 h^-1. This work simultaneously addresses two critical bottlenecks─vapor diffusion suppression and salt accumulation─through a simplified structural design, providing an important scientific and applied paradigm for evaporator design.