Photothermal Water Evaporation of Zwitterionic Copolymer/Polypyrrole Composite Cryogels

During the interfacial photothermal water evaporation process of seawater, salt crystallization significantly reduces the evaporation efficiency of the evaporator. To address this challenge, a series of zwitterionic copolymer cryogels were synthesized through cryogenic copolymerization of the zwitterionic monomer, sulfobetaine methacrylate, and the hydrophilic monomer, acrylamide. Subsequently, a photothermal water evaporator was constructed by in-situ loading polypyrrole via oxidative coupling polymerization. The salt resistance of the evaporator was enhanced through the anti-polyelectrolyte effect of the zwitterionic side groups and the water convection between the bulk water and the evaporation surface. To systematically clarify the dependence of equivalent evaporation enthalpy on copolymer composition and pore architecture, we optimized the copolymerization composition of cryogels. Scanning electron microscopy was used to observe the pore structures of cryogels with different compositions. Additionally, dark evaporation experiments were performed to determine their equivalent evaporation enthalpies. Under simulated one-sun illumination (incident intensity: 1 kW/m²), the evaporator achieved a maximum evaporation rate of 2.39 kg/(m²·h) for pure water. In 8 h seawater evaporation test, no salt crystallization was observed while the evaporator achieved a peak evaporation rate of 2.41 kg/(m²·h) with an average value of 2.23 kg/(m²·h). Notably, the quality of the collected water met the drinking water standards.