Robust seawater desalination and sewage purification enabled by the solar-thermal conversion of the Janus-type graphene oxide evaporator

The state-of-the-art structure design of solar-thermal evaporators demonstrating convenient manufacture, high evaporation rate, high energy efficiency and multiple environment evaporation is urgently needed in solar-driven low-energy water purification/harvesting. Herein, a novel Janus-type graphene oxide (GO) evaporator is proposed by chemical crosslinking to form integrated GO hydrogel and sunlight triggered partial reduction of top GO layer. The partially reduced GO (PRGO) nanosheets present an extremely high solar absorbance of 92.97%, leading to an efficient localized solar-thermal conversion. The porous and hydrophilic GO hydrogel facilitates the fast vertical water transport to the top PRGO photothermal layer. Taking advantages of the synergistic effect in the water-energy nexus, the Janus-type solar-thermal evaporator evaporates water with an ultra-high rate of 3.24 kg·m−2·h−1 via 99.98% energy efficiency from 1 sun irradiation with a low GO loading of 0.146 wt%. The Janus-type GO evaporator presents robust desalination and purification performances in simulated seawater, sewage and acidic/alkaline water. Furthermore, a portable solar-thermal water purification device equipped with the Janus-type GO evaporator desalts a real seawater far above the drinking water standard with a 99.99% salt rejection rate and removes 90.90% of total carbon in a real sewage, highlighting its potential for high-performance clean water harvesting.