3D printing double-layer hydrogel evaporator with surface structures for efficient solar steam generation

Solar interfacial evaporation has become promising recently because of the growing demand for clean water in human society, and improving the evaporation rate of evaporators is of great importance for efficient seawater desalination. In this work, a novel double-layer Janus hydrogel evaporator with surface structure was fabricated by 3D printing using poly(ethylene glycol) diacrylate (PEGDA) with small amount addition of carbon black (CB), sodium alginate (SA), and sodium lignosulfonate (SL). The printed hydrogel has excellent abilities as a solar evaporator, such as high solar absorption, low thermal conductivity, desired hydrophilicity, and strong mechanical strength. Compared with the traditional 2D evaporators, our evaporator can significantly reduce the evaporation enthalpy of water and localize heat on the interface, these positive effects lead to a high evaporation rate of 2.78 kg·m⁻²·h⁻¹ of our evaporator with an energy efficiency of 91.5 % under 1 sun, which is significantly higher than the theoretical evaporation rate limit of 2D evaporators (1.46 kg·m⁻²·h⁻¹) and outperforms the PEGDA-based hydrogel evaporators reported in the literature. Furthermore, this Janus evaporator shows good anti-fouling and wastewater treatment performances. This research promotes the applications of 3D printing hydrogel evaporators through a novel strategy.