Reduced graphene oxide incorporated triple network hydrogels for enhancing solar desalination performance

Solar-driven hydrogel evaporator has attracted great attention in desalination recently. However, it remains a challenge to develop high performance hydrogel evaporators with outstanding mechanical property, high evaporation efficiency and excellent durability. In this study, 2-hydroxyethyl methacrylate (HEMA), sodium alginate (SA) and graphene oxide (GO) were employed for fabricating triple network hydrogels, which were used for solar desalination. The hydrogels were composed of poly(2-hydroxyethyl methacrylate) (PHEMA), SA and reduced graphene oxide (rGO) networks. The rGO network could well wrap on PHEMA and SA networks, forming an interpenetrated structure with good mechanical property. After being reduced of GO, the PHEMA/SA/rGO hydrogels showed excellent solar absorption and evaporation performance due to better photothermal effect of rGO than that of GO. Due to outstanding light absorption characteristic, the as-prepared hydrogels showed maximal energy efficiency of 95.59 % under one sun illumination. The hydrogel evaporator also exhibited excellent reusability for effective desalination. This stable performance may be attributed to its enough water molecules embedded in the crosslinked network, which prevented salt supersaturation. The outdoor solar desalination experiment suggested that concentration of four typical ions (Na+, Mg2+, K+, Ca2+) in purified water fully met drinking water standards. This work may provide a new idea for design and creation of hydrogel evaporator with high mechanical strength and solar energy conversion efficiency for solar steam generation.