Construction of highly efficient solar-driven evaporator based on guar gum and zwitterionic polymers

To tackle the worldwide water scarcity challenge, it is crucial to advance sustainable solar-powered interfacial evaporation systems that are both highly efficient and eco-friendly. In this study, a novel multifunctional composite hydrogel evaporator is developed through a one-step copolymerization-crosslinking strategy that integrates sustainable bio-based guar gum (GG), a zwitterionic polymer (PSBMA) with excellent anti-polyelectrolytic property, highly efficient photothermal material carboxylated carbon nanotubes (CNT-COOH), and melamine foam (MF) served as a supporting framework to ensure structural stability. This composite hydrogel effectively overcomes the limitations of single materials in photothermal conversion, structural stability or hydraulic transmission through the synergistic effect of its components. The results show that under one solar irradiation, the optimized sample achieves an evaporation rate of 2.59 kg m^-2 h^-1, corresponding to an efficiency of 80.23%, which is notably superior to the control groups lacking either CNT-COOH or SBMA, which exhibit rates of 1.11 kg m^-2 h^-1 and 1.91 kg m^-2 h^-1, respectively. Moreover, this evaporator still demonstrates excellent stability and reusability. Thanks to the strong water-holding and anti-salt properties of these polymers and the stable photothermal performance of CNT-COOH, this evaporator demonstrates excellent long-term stability with no salt crystallization after continuous operation for 10 cycles and no significant performance decline. Additionally, it exhibits outstanding removal capabilities for various ions and organic pollutants. This study offers significant understanding and practical approaches for designing high-performance, anti-pollution, and durable solar water purification devices based on bio-based materials.