In situ polymerized Fe2O3@PPy/chitosan hydrogels as a hydratable skeleton for solar-driven evaporation

The world population is severely affected by water scarcity, and it is an alarming issue that needs to be addressed urgently. Seawater desalination by solar-driven evaporation is a promising technique to produce clean water. However, it is energy intensive and directs to a low water yield under natural sunlight. Therefore, the developments of new photothermal materials can reduce required energy for desired evaporation rates for efficient freshwater yield. Indeed, chitosan and polypyrrole-based polymers are natural cationic copolymers, and their nanocomposites present well deal of interest for hydrogel structures due to their hydratable skeletons, and solar-absorbing nature. Here, we report in situ polymerized Fe 2 O 3 @PPy/chitosan hydrogels as lightweight evaporation structures for solar-powered evaporation under brine solutions (3.5 wt%). The polymeric network of Fe 2 O 3 @PPy/chitosan hydrogels builds in cross-linked macroporous water channels, self-floating, and a wide range of omnidirectional solar absorption (96%). The state-of-the-art evaporation experiments demonstrate an efficient evaporation rate of water (1.80 kg m –2 h –1 ) and enhanced solar-to-vapor conversion efficiency (91%) as compared to other carbon-based evaporation structures, excluding heat losses under 1 kW m –2 (one sun). Of note, the ultra-black hydrogel surface stored enough thermal energy (39.6°C) under one sun solar irradiance due to the cationic polymeric network of Fe 2 O 3 @PPy/chitosan. A single-step process for a freshwater supply that has been purified from various contaminants shows the potential of this device for real-world applications.