Extremely Black Vertically-Aligned Carbon Nanotube Arrays for Solar Steam Generation.

The unique structure of a vertically-aligned carbon nanotube (VACNT) array makes it behave most similarly to a black body. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the high efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination, the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and heat localization by the thin layer of VACNTs. We found the evaporation rate of water assisted by VACNT arrays is 10 times of that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and heat localization induced by the VACNTs layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.