Sponge-like PAM/PANI composite hydrogel evaporator for high-efficiency solar-driven Interface water evaporation

Solar-driven interfacial evaporation represents an ideal strategy to alleviate freshwater scarcity and environmental issues, showing great promise in desalination and sewage treatment. However, fabricating evaporators with efficient vapor generation, rapid water supply, and long-term stability remains a significant challenge on practical applications. Herein, a sponge-like composite hydrogel interfacial evaporator with polyacrylamide (PAM) hydrogel as hydrophilic matrix and polyaniline (PANI) as photothermal component is developed through a combination of cononsolvency photopolymerization of PAM and in-situ oxidative polymerization of PANI. The cononsolvency effect results in the evolution of the PAM hydrogel's internal pore structure from closed-cell structure to sponge-like open porous network with continuous microchannels, which greatly facilitates the efficient transportation of water within the hydrogel matrix. Thanks to the highly interconnected spongy pore structure as well as the excellent light-to-heat conversion capacity of PANI, after the in-situ oxidative polymerization of PANI, the optimized sponge-like PAM/PANI hydrogel interfacial evaporator shows a high-efficiency solar evaporation rate of 2.15 kg m^-2 h^-1 and energy efficiency of 96% with excellent salt-resistance feature and long-term operational stability. Notably, through integrating cononsolvency photopolymerization with DLP 3D printing technique, PAM/PANI composite hydrogel evaporator with 3D architectures featuring conical array on surface was fabricated directly, which greatly increases the lateral evaporation surface and enhances solar utilization exploited by multiple light reflections. As a result, the solar evaporation rate of 3D-PAM/PANI composite hydrogel evaporator increased further to 3.73 kg m^-2 h^-1 without sacrificing salt-resistance feature and long-term operational stability. Meanwhile, the 3D-PAM/PANI evaporator also shows great potential for applications in seawater desalination and wastewater purification in both laboratory and practical outdoor conditions. Benefiting from all these excellent characteristics, the proposed sponge-like PAM/PANI composite hydrogel evaporator exhibits promising potential for sustainable desalination and treatment of high-salinity brine over extended operational periods.