Nanosized amorphous and nanocrystalline titania doped by Cr as novel, efficient, and cost-effective cool-colored nanopigments

Abstract

Ceramic cool-colored nanopigments (NPGs) are becoming more promising in painting applications for their cooling and aesthetic performance. The phase structure and the doping by color elements play a crucial role in the performance of nanopigments. Throughout this study, pure titania (TiO2) and chromium (Cr)-doped TiO2 NPGs in nanosized amorphous and nanocrystals structures were synthesized using a simple hydrolysis route. The molar ratios of chromium (III) acetate hydroxide: titanium tetra isopropoxide are 0%, 5%, 15%, and 25%. The synthesized NPGs were studied as-synthesized and after annealing at 500oC and 700oC. X-ray diffraction analyses, FTIR and high-resolution transmission electron microscope (HRTEM) were utilized to explore the microstructure and property of the synthesized NPGs. Also, surface area of the synthesized NPG samples was estimated by BET measurement. Optical property of synthesized NPGs was specified by UV/Vis/NIR spectroscopy. The combined influences of the annealing temperature and Cr addition on the phase structure, grain growth and near infrared (NIR) reflectivity of NPGs have been investigated. Pure white TiO2 NPG annealed at 700oC was displayed the higher NIR solar reflectance (R* = 94.72%) than the other investigated NPGs. The presence of Cr ion in annealed TiO2 NPGs caused a massive reduction in R* which is reaching out to 21.5% for the highest Cr concentration with annealing at 700oC. While the NIR reflectivity of as-synthesized pure TiO2 was slightly reduced from 87.49% to 77.05% as Cr ion content was increasing. The reflectance parameter in the visible region (RVIS*) was determined for the studied NPGs to define their aesthetic performance. Moreover, the color coordinates CIE (L*, a* &b*) and (ho, C*) were presented for the investigated NPGs according to the perpendicular form and the polar form, respectively.