Double-Shell Black TiO2 Hollow Nanospheres with an Inner White Layer for Enhanced Near-Infrared Reflectance for Autonomous Driving Applications

초록

In this study, black double-shell TiO2 hollow nanospheres with an inner white shell (wBDST-HNs) are successfully synthesized as high near-infrared (NIR)-reflective pigments for LiDAR-recognizable black coatings in autonomous driving applications. Specifically, the wBDST-HNs are prepared through a sequential process involving sol?gel synthesis using titanium isopropoxide (TTIP), sodium borohydride (NaBH4) reduction, and ammonium hydroxide (NH4OH) etching to generate the double-shelled hollow architecture. The resulting nanospheres are dispersed in a hydrophilic varnish and spray-coated onto various substrates to form uniform black coatings. This integrated approach enables the formation of Ti3+-rich black TiO2 while simultaneously introducing an inner white shell that enhances optical reflectance through multiple internal light scattering. As a result, the wBDST-HN coatings exhibit a remarkably high NIR reflectance of 40.3 % at 905 nm with complete blackness in color. The superior NIR response and stable coating uniformity demonstrate the potential of wBDST-HNs as advanced black pigment materials for LiDAR-detectable autonomous vehicle coatings. - This research was partly supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant No. RS-2025-25437329 and RS-2025-25396489), and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (grant No. RS-2025-16070620). Keywords: Autonomous driving systems; LiDAR sensor; black double-shell TiO2 nanospheres; Near-infrared; paint formulation.