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.