Hydrogel-based 3D evaporator with cross-linked fixation by carbon dots for ultra-high and stable solar steam generation

Solar-driven water steam generation had been recognized as a promising strategy to address water scarcity in an environmentally friendly and cost-effective manner, and the development of an evaporator capable of efficient evaporation and stable long-term operation remains a huge challenge in the field. Herein, a three-dimensional (3D) hydrogel-based evaporator consisting of sodium alginate (SA), polyvinyl alcohol (PVA) and carbon dots (CDs) integrated into a melamine sponge (MS) structure was constructed, in which the CDs were firmly bonded to the SA/PVA double crosslinked network through hydrogen bonding, which improved the mechanical properties and load-bearing capacity of the evaporator. Crucially, as highly efficient light-absorbing carbon-based materials, the CDs were homogeneously dispersed in the hydrogel, significantly enhancing the photothermal conversion capability of the evaporator. The test results indicated that the evaporation rate of the 3D-CDs/SA/PVA-MS evaporator reached up to ultra-high solar steam generation rate of 4.79 kg m-2h−1 in 3.5 wt% NaCl solution at 1 sun irradiation, and exhibited the relatively excellent evaporation rate (4.13 kg m-2h−1) in high saline seawater (25 wt%). This study aimed to provide a simple and reliable modification method to enhance the evaporation performance and improve the hydrogel network of SA/PVA-based hydrogel evaporator and demonstrate their potential applications in seawater desalination and purification.