Janus carbon nanotube sponges for highly efficient solar-driven vapor generation

The complex balance between light absorption and water transport in a porous light absorber plays a crucial role in solar-driven vapor generation. We demonstrate that light absorption and water transport can be separated in a Janus carbon-nanotube-sponge (CNTS) based light absorber. Light absorption mainly occurs in the top layer of hydrophobic CNTs with broadband light absorption and water is wicked up to porous CNTS through channels in bottom hydrophilic layer. Solar energy loss to water is significantly reduced due to the separation of light-absorbing layer and water-wicking layer. The Janus CNTS achieves the evaporation rate of 3.0 kg m-2h−1 under one sun irradiation and the energy transfer efficiency of 95 %. Highly efficient water transport, high light absorption and good long-term stability make Janus CNTS ideal for use in the desalination of brackish water.