Highly efficient solar desalination enabled by a spiral-layered hydrogel with omnidirectional salt rejection

Solar-driven interfacial evaporation holds great potential for seawater desalination, yet its efficiency and long-term viability are critically hindered by salt crystallization. Herein, we develop a spiral-layered hydrogel (SLH) solar evaporator to overcome these persistent challenges. The SLH features a layered architecture with non-uniform pore sizes across its upper and lower layers, ensuring adequate water supply to the evaporation interface while minimizing heat loss to the bulk water. Coupled with high light absorption and reduced evaporation enthalpy, the SLH achieves an impressive evaporation rate of 4.7 kg m-2 h-1. The Janus structure of the SLH suppresses salt crystallization on the surface, while the omnidirectional groove configuration and spiral flow dynamics synergistically prevent salt ion accumulation within the pores. Furthermore, the electronegativity of graphdiyne (GDY) surface together with conjugate two-dimensional plane, act as a barrier to chloride ion infiltration. In a 20 wt% NaCl solution, the cost-effective SLH maintains a robust evaporation rate of 4.23 kg m-2 h-1 over an extended period of 20 days. Outdoor validation with a cylindrical prototype demonstrated a maximum freshwater collection rate of 1.8 L m-2 h-1. Such functional design and salt management strategy may provide possible prescriptions to salt accumulation challenges, establishing a foundation for sustainable and high-efficiency water production systems.