TiO2@CoTiO3 complex green pigments with low cobalt content and tunable color properties

Green complex pigments with TiO₂@CoTiO₃ core–shell structure were prepared through calcination of precursors obtained from the precipitation of Co²⁺ on TiO₂ particles. The synthesized pigments were characterized by colorimetry, near-infrared diffuse reflectance spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet–visible (UV–vis) spectroscopy. The pigments were found to consist of a rutile TiO₂ core and outer ilmenite CoTiO₃ shell. The green pigments with good color properties could be obtained via calcination of the precursors at 800 °C. The pigments with Co/Ti ratio of 0.4 had the highest green component value and exhibited good color properties (L*=49.51, a*=?34.58, b*=5.53). The color properties could be tuned by just changing the Co/Ti ratio. The as-prepared complex pigments exhibited an enhanced near-infrared reflectance compared with pure CoTiO₃ pigments and also exhibited better color properties than the mixed pigments of TiO₂ and CoTiO₃. Further, the complex pigments had much lower consumption of cobalt compared to pure CoTiO₃ and Co₂TiO₄ pigments. The special core–shell structure was found to be responsible for the enhanced near-infrared reflectance and good color properties.