Plasmonic Graphene Polyurethane Nanocomposites for Efficient Solar Water Desalination

Solar energy is the cleanest and most abundant renewable natural resource available. Materials for solar photothermal energy conversion are highly sought after for their cost savings, clean environment, and broad utility in providing water heating and/or steam for many applications including domestic water heating and solar-driven desalination. Water desalination via solar steam generation is considered one of the most important technologies to address the increasing pressing global water scarcity. The current solar thermal systems rely on the use of copper or aluminum for absorbers which have limited utility because of their inflexibility for tailored applications, high cost, and limited availability. These bulk metals are not very efficient in absorbing the solar spectrum. Therefore, the current solar thermal desalination devices have low efficiency and low water productivity due to the ineffectiveness of solar collectors to convert most of the sun energy into heat. Herein, we report the development of a new generation of highly efficient, flexible, low weight, highly porous, and cost-effective plasmonic graphene polyurethane (PGPU) nanocomposite materials for solar steam generation through the efficient evaporation of surface water pools. The PGPU nanocomposites contain metallic nanoparticles that exhibit very strong solar absorption. The metal nanoparticles (0.2 wt %) incorporated within the 0.5 wt % graphene oxide (GO)-polyurethane (GOPU) nanocomposites absorb sunlight much more efficiently than bulk metals or carbon materials. Subsequent nonradiative relaxation causes absorbed energy to be converted into heat which can be controlled by the size, shape, and organization of the metal nanoparticles within the PGPU materials. The polyurethane (PU) foam provides a hydrophilic surface with abundant microporous structure, excellent thermal insulation properties, and facile and scalable synthesis. The PGPU nanocomposites are produced as porous foams that float on top of the evaporating water pools which significantly enhance the absorption of the solar energy and the high solar thermal conversion efficiency. The PGPU nanocomposites containing 0.2 wt % Au and Ag nanoparticles are demonstrated to be among the most efficient solar thermal converters reported to date for solar water desalination. The Au/Ag-PGPU foams exhibit average water evaporation rates of 1.00, 6.59, and 11.34 kg m–2 h–1 with superb solar thermal efficiencies of up to 63%, 88%, and 96.5%, under 1, 5, and 8 sun illumination, respectively. Furthermore, the PGPU foams display stable evaporation rates over more than 10 repeated evaporation cycles without any performance decline. The high solar thermal evaporation efficiency, excellent stability, and long-time durability make the PGPU nanocomposites excellent candidates for applications in solar steam generation and seawater desalination.