A bridge-arched and layer-structured hollow melamine foam/reduced graphene oxide composite with an enlarged evaporation area and superior thermal insulation for high-performance solar steam generation

Interfacial solar steam generation has been proved to be effective for desalination and water purification applications and a large number of smartly designed structures have been reported to reduce the heat conduction loss into bulk water by introducing thermally insulating porous foams. Actually, directly using air as the thermal insulation layer should be one of the most efficient ways to reduce the heat loss into bulk water. To this end, we present a bridge-arched hollow and self-floating integrative solar absorber/water evaporator prepared by a one-step hydrothermal reaction. The fully integrative water evaporator can achieve similar to 92.9% water evaporation efficiency and 1.476 kg m(-2) h(-1) water evaporation rate under just 1 sun illumination. Such a high efficiency is caused by the unique bridge-arched raised upper surface, hollow interior, and tailored bilayer structure consisting of hydrophilic porous melamine foam for water transportation and a reduced graphene oxide layer for photothermal conversion. These features not only provide broadband solar absorption (similar to 95%), efficient light-to-heat conversion and a high water evaporation rate, but also suppress the heat loss at the same time. Owing to the simplicity of fabrication and recyclability, this novel composite structure is an ideal material for commercial, portable solar thermal conversion applications to obtain clean water via seawater desalination and wastewater purification.