Designing a highly near infrared-reflective black nanoparticles for autonomous driving based on the refractive index and principle.

Hypothesis: The development of highly NIR reflective black single-shell hollow nanoparticles (BSS-HNPs) can overcome the Light Detection and Ranging (LiDAR) sensor limitations of dark-tone materials. The crystalline phase of TiO and the refractive index can be controlled by calcination temperature. The formation of hollow structure and the refractive index is expected to simultaneously increase the light reflection and LiDAR detectability.

Experiments: The BSS-HNPs are synthesized using the sol-gel method, calcination, NaBH reduction, and etching to form a hollow structure with true blackness. The computational bandgap calculation is conducted to determine the bandgap energy (E) of the white and black TiO with different crystalline structures. The blackness of the as-synthesized materials is determined by the Commission on Illumination (CIE) L*a*b* color system.

Findings: The hydrophilic nature of BSS-HNPs enables the formulation of hydrophilic paints, allowing the mono-layer coating. With the synergistic effects of hollow structure and the refractive index, BSS-HNPs manifested superb NIR reflectance at LiDAR detection wavelengths. The high detectability, blackness, and hollow structure of BSS-HNPs can expand the variety of LiDAR-detectable dark-tone materials.