Intelligent solar-driven “switch” photothermal hydrogel for clean water harvesting

Abstract

Water shortage is becoming a huge challenge to mankind. Inspired by pufferfish, we developed an intelligent solar-driven “switch” hydrogel system PEG-PNIPAAm/Fe3O4 hydrogel (PPFH). This hydrogel system is characterized by a uniform porous network structure formed by the integration of hydrophilic PEG, temperature-responsive PNIPAAm polymer and Fe3O4 photothermal nanoparticles. The three-dimensional porous structure provides a higher surface area, offering more adsorption sites for water molecules. The interaction between PPFH and water primarily relies on the hydrogen bonding between the amide groups in PNIPAAm and water molecules, which enhances the hydration of the hydrogel network for rapidly water harvesting. However, when exposed to sunlight, the presence of Fe3O4 nanoparticles causes the ambient temperature to rise rapidly above the LCST, the hydrogen bonding between molecules gradually weakens, while the hydrophobic interactions among the hydrophobic groups in PNIPAAm become stronger, causing the polymer chains to contract and water releasing. The fog capture performance of PPFH can reach up to 3.2 g g−1, and under the irradiation of a sunlight (1 kW m−2), the captured water can be released within 8 min, and the water release efficiency reaches 94 %. This design concept provides the possibility for promoting the widespread implementation of hydrogels-based solar evaporators in practical purification systems in the future, alleviating water shortages issues.