Excellent salt tolerance and rich intermediate water for carbon-based hydrogel from non-covalent interaction

Hydrogels are attracting more and more attention in solar interfacial water evaporation due to their highly tunable physicochemical structure. In particular, the electrostatically-based polyelectrolyte hydrogel evaporator not only effectively activate water molecules through charged functional groups but also hinder the transport of charged ions in saline solutions, achieving a balance between high evaporation performance and excellent salt resistance. However, single-component polyelectrolyte hydrogels carry only one type of charge, and the inevitable repulsive interaction creates space to accommodate free water, resulting in a reduction of intermediate water content, thereby negatively impacting efficient water evaporation. Here, we introduce a carbon-based hydrogel evaporator fabricated by combining a hydrogel prepared from sodium alginate and chitosan via non-covalent interaction with coal pitch-based porous carbon. The electrostatic attraction between these two oppositely charged components minimizes the inter-chain gaps in the hydrogel, increasing the intermediate water content to 74.8 %. Additionally, the charged functional groups effectively restrict the transmission of charged ions in the salt solution during desalination processes, overcoming the challenge of salt blockage. Therefore, the evaporator achieves an evaporation rate as high as 2.10 kg m −2 h −1 and demonstrates excellent salt resistance in a purification test using nearly-saturated saline water.