Nanostructured FeO/TiO composite particles with enhanced NIR reflectance for application to LiDAR detectable cool pigments.

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