Near-infrared reflecting inorganic pigments based on Fe3⁺-doped TiO2 prepared via the sol-gel method: characterization and chromatic properties

Novel Ti 1-x Fe x O 2 pigments ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>x</mml:mi> <mml:mo>=</mml:mo> <mml:mi> </mml:mi> </mml:math> 0-0.2) were successfully synthesized via the sol-gel method. Fe³⁺ doping preserved the rutile phase structure of TiO 2 while suppressing crystal growth; as the Fe content increased, the color of the pigments gradually transitioned from light red to deep red and further to reddish-brown. Among them, Ti 0.9 Fe 0. 1 O 2 calcined at 700 ℃ exhibited the optimal red hue ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>*</mml:mi> </mml:mrow> </mml:msup> <mml:mo>=</mml:mo> <mml:mi> </mml:mi> </mml:math> 25.7), while Ti 0.95 Fe 0. 0 5 O 2 treated at 800 ℃ demonstrated the best near-infrared reflectance performance (73.62 %). All samples showed notably higher reflectance in the NIR range compared to a commercial iron-oxide pigment of similar color (44.25 %). Furthermore, chromatic property tests after acid/alkali corrosion, together with thermogravimetric-differential scanning calorimetry analysis, confirmed the good chemical and thermal stability of this series of pigments. These energy-saving pigments show promising potential for application in high-efficiency energy-efficient building materials such as solar heat-reflective functional artificial stones.