Nanostructured Fe2O3/TiO2 composite particles with enhanced NIR reflectance for application to LiDAR detectable cool pigments

Abstract

Nanostructured Fe₂O₃/TiO₂ composite pigments with improved NIR reflectance were prepared by a homogeneous precipitation method using urea and NH₄OH. The optical and morphological properties of the resulting pigment were investigated by varying the weight ratio of Fe₂O₃ to TiO₂ and the calcination temperature. The resulting composite pigment has a nanostructure in which Fe₂O₃ nanoparticles of 20–30 nm size are well coated on the surface of TiO₂ (∼100 nm) and the reflectance is greatly improved in the wavelength range of 620–1350 nm. The ratio of Fe₂O₃ to TiO₂ and the calcination temperature were optimized to provide both high NIR reflectance and red color, which were 0.1 and 700 °C. As a result, compared with pure Fe₂O₃ (E_g = 2.06 eV, a* = 22.6), the optimized Fe₂O₃/TiO₂ composite pigment (E_g = 2.09 eV, a* = 24.8) showed similar color properties and improved NIR reflectance by about 23.8%. In addition, the Fe₂O₃/TiO₂ composite pigment showed about 62.7% larger reflectance at 905 nm than Fe₂O₃. According to a temperature rise test under IR illumination, the Fe₂O₃/TiO₂ composite pigment was confirmed to have improved heat shielding properties. Therefore, the nanostructured Fe₂O₃/TiO₂ powder could be potentially applied as a LiDAR detectable cool red pigment for autonomous vehicles.