Conversion of Solar Radiation into Vapor: New Possibilities Offered by Nanomaterials (Review)

The current state in converting solar radiation into steam using nanotechnologies and nanomaterials is considered. The main attention is paid to the use of novel nanostructured materials, including graphene components to generate steam, in particular, to the use of the latter as floating or volumetric solar absorbers. The absorbers of the above types have been classified, their physical and technological characteristics have been considered, and preferable variants for various applications have been established. It is stressed that the question on the efficiency of surface or volumetric absorbers has to be considered as applied to specific applications. The thermophysical processes that occur during the radiation absorption and the heating of the nanofluid have been described for different absorption patterns. Models that underlie the description of the thermophotonics and nanoplasmonics processes during the solar radiation absorption by nanocomponents have been formulated. The basic processes that occur under nanoplasmonic heating of nanocomponents by solar radiation and the heat-and-mass exchange between nanocomponents and the surrounding medium have been investigated. Special attention is paid to steam generation by plasmonic nanoparticles and graphene flakes, which are currently considered the basic elements for prospective efficient solar radiation conversion systems. The properties of the materials used to absorb solar radiation and their components are described. The materials that have already shown a high solar absorption coefficient are listed. The properties of nanofluids used for volumetric absorption of solar radiation and the subsequent localized heating are described. The significant role of novel steam-generation mechanisms based on plasmonic nanoparticles and graphene flakes is stressed. Mesoscopic and nanostructured solar radiation absorbers are presented that ensure the generation of steam used not only to produce energy but also to desalinate and sterilize water. The main unsolved problems of applying nanocomponents for the solar thermal industry are considered and new tasks are set, the solution of which will allow taking important steps towards using the above systems for solar energy conversion.