Flame Synthesis of Super-Hydrophilic Carbon Nanotube/Ni Foams Decorated with Fe2O3 Nanoparticles for Water Purification via Solar Steam Generation.

Solar-driven water evaporation has been proposed as a renewable and sustainable strategy for generation of clean water from seawater or wastewater. To enable such technologies, development of photo-thermal materials that enable efficient solar steam generation are essential. The current challenge is to manufacture such photo-thermal materials cost-effectively and at scale. Further, the photo-thermal materials should be strongly hydrophilic and environmentally stable. Herein, we demonstrate facile and scalable fabrication of carbon nanotube (CNT) based photo-thermal nanocomposite foams by igniting an ethanol solution of ferric acetylacetonate (Fe(acac)3) absorbed within a Nickel (Ni) foam under ambient conditions. The Fe(acac)3 precursor provides carbon and the zero-valent iron catalyst for growing CNTs on the Ni foam; while ethanol facilitates the dispersion of the Fe(acac)3 on the Ni foam and supplies heat energy for the growth of CNTs by its burning. A forest of dense and uniform CNTs decorated with Fe2O3 nanoparticles are generated within seconds. The resultant Fe2O3/CNT/Ni nanocomposite foam exhibits "super-hydrophilicity" and high light absorption capacity, ensuring the rapid transport and fast evaporation of water within the entire foam. Efficient light-to-heat conversion causes the surface temperature of the foam to reach ~83.1 oC under 1 sun radiation. The average water evaporation rates of such foams are as high as ~1.48 and ~4.27 kg m-2 h-1 with light-to-heat conversion efficiencies of ~81.3% and ~93.8% under 1-sun and 3-sun radiation, respectively. Moreover, the versatile and scalable combustion synthesis strategy presented here, can be realized on various substrates, exhibiting high adaptability for different applications.