A magnetic nanostructure PAC@Fe3O4 driven design toward Janus hydrogel achieves highly efficient solar water evaporation

Solar water purification is a promising scheme to relieve the energy crisis and clean water shortages. In order to improve the efficiency of producing water, it is necessary to develop a novel photothermal conversion interface to manage heat loss and boost water evaporation efficiency. Herein, a Janus hydrogel evaporator of powder active carbon (PAC) and Fe3O4 in polyvinyl alcohol (PVA) and polystyrene sulfonate (PSS) cross-link hydrogel, called CFPS, is explored as the light absorber for broadband light absorption and formed a hydrogel network of the multi-hydrophilic group. Its hydrophilic/hydrophobic structure of CFPS is used to regulate heat loss and promote water transport, which can attain lower evaporation enthalpy and a higher evaporation rate. Specifically, the surface temperature of the CFPS can reach around 45 degrees C and 93.4% energy utilization efficiency under 1 sun illumination. In the comparison of the analogous Fe3O4-based evaporator, CFPS has the higher static evaporation rate with 3.43 kg m-2h- 1. Besides, it has great mechanical properties, durability and anticrystallization function, which can be adapted to the water purification scene of wastewater and hypersaline water desalination. This photosensitive magnetic hydrogel evaporator shows potential in the scenarios of wastewater purification and desalination.