High-efficiency evaporation and concentration with exceptional salt resistance via a chitosan annular hydrogel...

To address the challenges of salt accumulation and limited evaporation rates in solar-driven interfacial evaporation systems under high-salinity environments, this study designed and fabricated an annular hydrogel evaporator with radially aligned channels based on the hydrophilic groups and cross-linked network properties of chitosan. This design significantly reduces material consumption while synergistically enhancing the evaporation rate and ambient energy harvesting capacity through a substantial increase in the Evaporation Area Index and intensified internal thermal convection, achieving an evaporation rate of 4.29 kg·m^-2·h^-1 and a 6.7-fold improvement in volumetric evaporation efficiency. To further enhance long-term operational stability under extreme salinity, a top-active water supply strategy was introduced, which effectively clears concentrated salt ions at the evaporation interface via precise flow control, maintaining stable evaporation without salt deposition even in 25 wt% high-salinity brine. Outdoor experiments demonstrated that the system can not only continuously produce freshwater meeting WHO standards at a rate of 11.53-15.36 kg·m^-2·d^-1, but also simultaneously achieve efficient brine concentration (concentration ratio: 1.16-2.29) and effective purification of heavy metals and organic dyes. Leveraging the core properties achieved through chemical structure modulation of chitosan-such as low evaporation enthalpy, high hydrophilicity, and stable salt rejection-this technology can be extended to concentration-dependent processes including brine mineral recovery and crystal purification, establishing a new paradigm for such applications. This design strategy also opens a new pathway for the broader application of carbohydrate polymers in sustainable water treatment and resource recovery.