A portable and washable solar steam evaporator based on graphene and recycled gold for efficient point-of-use water purification

A solar steam evaporator provides a sustainable and efficient alternative water purification solution to address the global freshwater shortage. Previous efforts have made significant advances in maximizing its water evaporation rate, but no single evaporator has all the properties necessary for practical point-of-use application, including a high efficiency for generation of drinkable water, an excellent portability critical for on-site water purification, good washability for mitigating evaporator fouling, and good reusability. We report a strategy to produce a high-performance photothermal material for point-of-use water purification. By simultaneously incorporating graphene and gold particles grown from recycled electronic waste in a mechanically strong sponge, we achieved highly efficient water purification under realistic conditions. In addition to a high evaporation rate (3.55 kg/m²/h under one-sun irradiation) attributed to a control of atomic structure of graphene and the size-dependent surface plasmon resonance of gold nanoparticles, it is portable which can be folded, vacuum compacted, dried and rehydrated without compromising performance. It also allows repeated washing to remove contaminant fouling so that it can be reused. The evaporator transforms various types of contaminated water into drinkable clean water, and can be mounted at any angle to optimize the incident solar irradiation. Furthermore, the assembled steam evaporator device could gain purified water meeting the World Health Organization drinking water standards with a high evaporation rate of 9.36 kg/m²/h under outdoor sunlight.