Salting-out/sacrificial template strategy for the preparation of hydrogels as efficient solar evaporators

Hydrogels have recently emerged as promising solar evaporators due to their exceptional high evaporation rates. However, the high costs and complexity associated with the conventional freezing-thawing processes pose challenges that hinder their widespread application in large-scale solar evaporation systems. Herein, we present the successful attempt to prepare hydrogel-based solar evaporators using a salting-out/sacrificial template strategy, where salt particles serve as both salting-out agents and sacrificial templates. Without the need for freezing processes, we successfully synthesized polyvinyl alcohol (PVA) hydrogels, incorporating copper oxide and antimony-doped tin oxide particles as solar absorbers. It is demonstrated that the salting-out (Hofmeister) effect enables the cross-linking of PVA polymeric chains, imparting significant mechanical strength and durability to the hydrogels. Meanwhile, the use of salt particles as sacrificial templates creates well-developed microchannels of 100–300 μm within the hydrogels, enabling rapid water delivery. These hydrogels exhibited a solar-weighted absorptivity of 93.4 % and achieved solar evaporation rates exceeding 3.0 kg m-2h−1 under one-sun illumination. Notably, their performance is comparable to that of state-of-the-art hydrogels prepared using freezing-thawing methods. As such, this proposed strategy holds great promise for the large-scale and cost-effective production of hydrogels as high-performance solar evaporators.