Polarized light and size control in modulating the photothermal performance of titanium nitride nanobipyramid

Plasmonic nanostructures have received considerable attention for solar photothermal conversion due to their strong light absorption and efficient heat generation. However, conventional noble-metal plasmonic materials suffer from high cost, limited thermal stability, and inadequate spectral matching with broadband solar radiation, restricting their practical applications. Titanium nitride (TiN) has recently emerged as a promising alternative owing to its favorable optical response, excellent thermal stability, and low cost. Nevertheless, a systematic understanding of how its photothermal performance depends on incident light conditions and structural parameters is still lacking. In this work, the photothermal properties of TiN nanobipyramids are systematically investigated using three-dimensional finite element simulations. The absorption and scattering characteristics under different incident directions and polarization states are analyzed, and the localized surface plasmon resonance (LSPR) mechanisms are elucidated through electromagnetic field and temperature distribution analyses. The results demonstrate pronounced optical anisotropy in TiN nanobipyramids. The strongest plasmonic resonance occurs under x-direction incidence with z-polarized light, yielding a maximum absorption cross section of 897.09 nm 2 at 830 nm and the highest steady-state temperature rise. Within the wavelength range of 300–1100 nm, TiN nanofluids exhibit excellent spectral matching with the AM1.5 standard solar spectrum, maintaining a solar absorption efficiency above 90% even at low volume fractions. Geometrical optimization reveals that the solar absorption efficiency first increases and then decreases with the variation of tip radius, which enables effective modulation of the photothermal performance of TiN nanobipyramids. The maximum solar absorption efficiency of 97.72% is obtained at a tip radius of 10 nm. These findings highlight the strong potential of TiN nanobipyramids for high-efficiency solar photothermal energy harvesting and thermal applications.