Investigation of photothermal heating enabled by plasmonic nanofluids for direct solar steam generation

Steam production has a wide range of applications such as seawater desalination, waste sterilization, and power generation. The utilization of solar energy for this purpose has attracted much attention due to its inexhaustibility and pollution-free nature. Here, direct solar steam generation at low-concentrated solar power using plasmonic nanofluids containing gold nanoparticles (Au NPs) was investigated experimentally. The key factors required for highly efficient solar steam generation, including Au NP concentration and solar power intensity, were studied in a simulated solar system by measuring the water weight loss and system temperature change. The best evaporation performance was obtained using a plasmonic nanofluid containing 178 ppm of Au NPs under 10 sun (1 sun = 1 kW m−2) illumination intensity, and the total efficiency reached 65%. However, the total efficiency of pure water was only 16%, which means that the plasmonic nanofluids reached a ∼300% enhancement in efficiency. Higher solar power led to a higher evaporation rate, higher specific vapor productivity (SVP), and higher Au NP concentrations resulted in better evaporation performance. Localized solar heating at the fluid-air interface was shown to contribute more to solar steam generation than to bulk fluid heating. Furthermore, the model of photothermal heating of plasmonic nanoparticle was established and the numerical results demonstrated the photothermal conversion process of plasmonic NPs from the light absorption to the heat dissipation into the bulk fluid.