A siphon-based spatial evaporation device for efficient salt-free interfacial steam generation

Solar-driven interfacial evaporation is an emerging alternative for alleviating the water crisis due to its sustainability and eco-friendly, but it still required efficient strategies to address the major obstacle of salt accumulation during high-rate evaporation processes. Herein, a spatial solar evaporation device with hydrogel-based evaporator and 3D printing module was fabricated to achieve excellent evaporation performance based on siphon phenomenon, in which carbon nanotubes were used as light absorber and coated on cotton fabrics via polyvinyl alcohol as binder. The 3D evaporator structure captured ambient energy efficiently to accelerate water vaporization. Coupling with the low evaporation enthalpy of intermediate water in PVA-hydrogel matrix, the evaporator exhibited fascinating evaporation rate of 4.55 ± 0.06 kg m−2 h−1 in siphon mode under 1.0 sun, which was ~3.2 times and ~1.8 times higher than the 2D floating and 2.5D hanging mode. Moreover, the design of siphon effect prevented the salt accumulation on the spatial evaporation device. Even for 20.0 wt% brine, there was no salt precipitating on the evaporator surface during a long-term evaporation (8 h), demonstrating the excellent stability and durability. In addition, the concentrated brine can be separated from the feed timely, avoiding the declined evaporation performance from increased feed salinity.