Photothermal‐Driven Structural Self‐Optimization Enables Marangoni‐Enhanced Stable Solar Desalination

ABSTRACT Solar‐driven interfacial evaporation (SDIE) offers a promising approach for sustainable water purification, yet hydrogel evaporators often suffer dehydration‐induced network deformation, uneven wetting, and salt accumulation under extended operation. Here, inspired by leaf transpiration and vein‐guided fluid transport, we introduce a photothermally driven structural self‐optimization strategy that converts dehydration‐induced hydrogel aging into functional evolution. Rapid heating of embedded multi‐walled carbon nanotubes (MWCNTs) under illumination triggers contraction of the polyvinyl alcohol hydrogen‐bond network, generating robust multiscale water‐distribution textures and vapor‐release channels. This structural adaptation amplifies interfacial temperature‐salinity gradients, thereby enhancing coupled thermo‐solutal Marangoni circulation for efficient energy utilization and sustained uniform wetting. The optimized hydrogel evaporator delivers a high evaporation rate of 5.71 kg m −2 h −1 under one sun illumination, ranking among the highest reported values for hydrogel‐based solar interfacial evaporators. It sustains salt‐free operation for 16 h in 3.5 wt.% brine and remains stable over 25 days of continuous day–night cycling at the higher salinity of 7 wt.%, demonstrating long‐term resistance to salt crystallization. It further confirms that the evaporation–condensation process enables efficient rejection of organic dyes, endowing the system with multifunctional capability for water treatment. This work demonstrates a generalizable design strategy for developing adaptive, durable, and high‐performance SDIE systems.