Spatially Janus‐Like Solar Evaporator with High Evaporation Rate and Enhanced Salt Processing Capacity

Abstract Solar‐driven interfacial evaporation with controllable salt crystallization provides an effective route toward zero‐liquid‐discharge desalination. However, conventional Janus evaporators often face intrinsic trade‐offs between high evaporation efficiency and controlled salt crystallization. Herein, a spatially distributed 3D Janus evaporator featuring an embedded conical evaporation core and peripheral hydrophilic water‐supply regions is proposed. By tuning the poly(vinyl alcohol)/chitosan ratio, robust double‐network hydrogels with interconnected porous channels are constructed, ensuring both mechanical stability and efficient water transport. The introduction of SiO 2 nanoparticles enables spatially graded hydrophilic‐hydrophobic interfaces, thereby achieving strong thermal localization, reduced water content at the evaporation surface, and regulated salt crystallization guided by geometric confinement. Experimental and theoretical analyses reveal that the conical‐core geometry optimizes the coupling between heat and mass transfer, maintaining stable evaporation and controlled crystallization even under high‐salinity conditions. Under 1 sun irradiation, the evaporator achieves an evaporation rate of 4.18 kg m −2 h −1 and a salt yield of 801 g m −2 h −1 , maintaining long‐term stability over eight light‐dark cycles (20 wt.% NaCl). This study presents a spatially engineered strategy for integrating efficient evaporation and directional salt collection, offering new insights for sustainable zero‐liquid‐discharge desalination and brine management.