Three-dimensional zwitterionic hydrogel-based evaporators with simultaneous ultrahigh evaporation rates and anti-fouling performance

Zwitterionic hydrogels (ZHs) are commonly adopted as evaporators to address the issues of low evaporation rate and poor salt resistance in solar-driven interfacial desalination due to their unique anti-polyelectrolyte (AP) effect. However, the inherent limitations of ZHs, including low water transfer rates compared to their evaporation rates and poor mechanical properties, have restricted their applications to two-dimensional (2D) evaporator configurations. Herein, we proposed a unique design of three-dimensional (3D) composite solar evaporators based on ZHs and polyvinyl alcohol (PVA) sponge to improve the water transfer capacity and mechanical properties of ZHs, and thus achieve ultrahigh evaporation rates and excellent anti-fouling performance. The porous structure and super hydrophilicity of PVA sponge endowed the prepared 5-cm-high ZH-based solar evaporators (ZHSE) with water transfer rates significantly faster than those without PVA sponge. In addition, the elastic PVA sponge component enhanced the mechanical properties of ZHSE, allowing it to easily fabricate 3D structures to obtain higher evaporation rates. Moreover, PVA sponge barely weakened the AP effect of poly(sulfobetaine methacrylate) (PSBMA) hydrogels in the ZHSE. Consequently, the evaporation rate of ZHSE reached 4.66 kg m-2 h-1 at 3.5 wt%, one of the highest among previous reports, attributed to the contributions from the 3D structural design of the evaporator and AP effect of ZHs. Meanwhile, ZHSE showed outstanding anti-fouling properties and excellent shape stability, working in 20 wt% brine ten hours a day for ten consecutive days without noticeable salt deposition and volume shrinkage. This work provides a new route to design high-performance hydrogel-based evaporators with high water transfer rates.