The optical properties of nanorods with curved slots for solar photothermal conversion

Nanofluids are one of the keys to improving solar energy utilization efficiency. Metal nanoparticles (MNPs) have narrow-band absorption limitations in photothermal conversion. Recent studies have shown that it can overcome narrow-band absorption by adding slots on the nanoparticles (NPs) to improve photothermal conversion efficiency. In this work, we investigated the effect of curved slots on the optical properties of Ag nanorods by the finite element method. The results show that the presence of the curved slot enables the Ag nanorods to excite multiple resonance absorption peaks in the wavelength range of 300–1100 nm. The curved slotting reduces the overall scattering of the Ag nanorods and enhances its spectral absorption in the visible and near-infrared regions. In addition, we also calculated and compared the photothermal conversion efficiency of nanorods and nanorods with curved slots. At f_v = 1 × 10⁻⁵ and h = 20 mm, the photothermal conversion efficiency of the curved slot Ag nanorods is increased by 6.8% over that of the Ag nanorods. In the measured volume fraction and fluid depth range, when the photothermal conversion efficiency reaches about 90%, the h and f_v required for nanorods with curved slots are about 0.64 times that of nanorods. Nanorods with curved slots only need a meagre volume fraction and fluid depth to achieve high photothermal conversion efficiency. We believe that the proposed curved slot metal nanorods can provide a feasible solution for solving the narrow-band absorption of nanorods and improving the efficiency of solar energy utilization.