Shape-dependent solar thermal conversion properties of plasmonic Au nanoparticles under different light filter conditions

In order to provide a relationship between nanoparticle (NP) parameters and irradiated lights when designing solar heating devices, shape-dependent solar thermal conversion properties of Au nanofluids at different irradiated lights were investigated experimentally and theoretically. Firstly, quasi-sphere and thorny Au NPs were successfully synthesized by a seed-mediated method, and the peak absorbance wavelength of which was located in ranges of 879–553 nm and 899–594 nm, respectively. Experimental results showed that the solar thermal conversion efficiency of Au nanofluids decreased with increasing NP size, which decreased from 86.0% to 58.6% when the NP size increased from 8.5 nm to 138.9 nm. Theoretical results indicated that for these large NPs, the scattering effect plays a major role in the solar thermal conversion process, and using the extinction coefficient to calculate the conversion efficiency may cause a substantial error. Furtherly it can be found that the solar thermal conversion efficiency of thorny Au nanofluids can achieve even 10% more than that of the quasi-sphere Au nanofluids. In addition, the temperature difference between the nanofluids and base fluid water under different incident light using a filter was found to be smaller than that of full solar spectra irradiation. The maximum efficiency of Au nanofluids was ∼61.7%, the enhancement of which reached ∼37.1% compared with water at an irradiation light with the wavelength of 500 nm.