Magnetic nanostructure and biomolecule synergistically promoted Suaeda-inspired self-healing hydrogel composite for seawater evaporation.

Multifunctional hydrogels with excellent comprehensive performance are essential prerequisite for the implementation of effective water resources technology with high efficiency and low energy consumption. Inspired by the water purification and self-healing properties of natural plants, and based on the synergy of photothermal and biological effects, high photothermal FeO nanoparticles and natural polyhydroxy oligomeric proanthocyanidin (OPC) are introduced into a water-active polyvinyl alcohol (PVA) hydrogel. Two new bio-hydrogels of PVA/FeO/graphite and PVA/OPC with self-healing and stretchable properties are proposed and designed. The obtained hydrogels exhibit reversible covalent cross-linked water-promoted healing (chemically) and photothermal melting/recrystallization healing (physically). The double-layered hydrogel composite demonstrates a dual response function (sunlight and near-infrared light), along with water purification properties. It is prepared through a water spray triggered self-healing process. The ultimate fracture strain of the photothermal layer and purification layer hydrogel was more than 1000% and 400% respectively after self-healing.After 48 h of hydrogel composite adsorption, the color of a methylene blue solution faded, and the absorption peak at 664 nm decreased. In addition, this research adopts a phased evaporation method to concentrate local energy and provide power for seawater evaporation. The evaporation efficiency of seawater induced by near-infrared (NIR) light was up to 3.15 kg m h, whereas that under sunlight was 1.25 kg m h. Selection of the evaporation excitation light source allowed control of the evaporation efficiency. The proposed technology is expected to be widely applicable to the staged evaporation of seawater as well as water purification.