In Situ Photothermalized Allomelanin Bulk Hydrogels Enable Efficient Solar Water Desalination

Hydrogel-based interfacial solar evaporation shows great promise for desalination. However, conventional hydrogels rely on exogenous photothermal agents, which may compromise water transport and complicate heat transfer within the hydrogel under conditions of high loading, insufficient dispersion, or poor interfacial compatibility. To address those critical issues, we have presented a facile and modular strategy for constructing robust allomelanin bulk hydrogels, where photothermal precursors (1,8-dihydroxynaphthalene) act as crosslinkers to directly couple with hydrophilic polymers (oxidized polysaccharides) for hydrogel gelation, while serving simultaneously as functional monomers that undergo spontaneous reactions to in situ form photothermal agents during the curing process. This strategy avoids the introduction of exogenous photothermal agents while achieving seamless integration of the in situ-generated photothermal agents with the hydrogel network, thereby remarkably boosting the performances of water transport, water activation, and thermal management. The resulting allomelanin bulk hydrogel interestingly achieved an impressive evaporation rate of 4.26 kg·m^-2·h^-1 under 1 sun irradiation. Moreover, techno-economic analysis estimated a competitive clean water production cost of $1.66 per ton for the hydrogel, rivalling reverse osmosis. This work pioneers a novel pathway for designing highly efficient hydrogel-based desalination devices, presenting a sustainable solution to water scarcity challenges.