Rapid fabrication of self-floating hydrogel foam with adjustable gas phase volume fraction for solar water evaporation

Combined with the evaporation enthalpy reduction, excellent water transportation of hydrogel and simplified evaporator structure of self-floating ability, hydrogel foam was regarded as one of effective materials for solar water evaporation. Nevertheless, synthesis methods for preparing hydrogel foams with controllable pore structures remain to be developed, and the mechanism by which the foam structure influences evaporation performance is yet to be fully understood. Herein, Tannic acid (TA) was utilized for photothermal conversion through chelation, and TA-Fe 3 + /Tempo-CNF/PAM hydrogel foam (TFCPF) with reduced heat conductivity, excellent water adjustment and self-floating ability was synthesized for solar evaporation. Taking the advantage of the self-catalyst system of TA and Fe 3+ , a rapid and convenient synthesis method of hydrogel foam was introduced. Moreover, throughout the syringe-pulling method, the gas phase volume fraction of hydrogel could be controlled precisely. Influenced by the volume fraction, the foam structure and floating condition on evaporation performance was discussed. The fast fabrication and controllable foaming method of TFCPF provided a novel and brief method for the fabrication of hydrogel foam that could be used for solar water evaporation without any additional water transportation or heat insulation structure. With closed-cell structure and high gas phase volume fraction, TFCPF-3 achieved the evaporation rate of 1.85 kg·m −2 ·h −1 and efficiency of 82.61% with reduced heat conductivity and evaporation enthalpy, while the hydrophilic double-network structure provided excellent mechanical robustness and salt resistance, enabling stable seawater desalination.