Synthesis and Characterization of Yellow Pigments (Li0.4RE0.6Al0.6)1/2MoO4–BiVO4 with High NIR Reflectance

In this work, a new type of near-infrared (NIR) reflective yellow pigment with a general formula of [(Li0.4RE0.6Al0.6)x/2Bi1–x][MoxV1–x]O4 was prepared by a solid-phase reaction calcined at a high temperature of 700 °C. X-ray diffraction (XRD), scanning electron microscope (SEM), a UV–vis–NIR spectrophotometer, and other methods were used to characterize the structure, morphology, and optical properties of synthetic pigments. For a series of [(Li0.4RE0.6Al0.6)x/2Bi1–x][MoxV1–x]O4 pigments, when x > 0.2, bismuth vanadate changes from the monoclinic phase (space group I2/b(15)) to the tetragonal scheelite phase (space group I41/a(88)). The structures of the pigments are all tetragonal scheelite phases, and the difference in their color rendering is mainly due to the differences between the valence band and the conduction band and the difference in the band gap caused by different rare earth elements. The NIR reflectance (R %) and NIR solar reflectance (R* %) of [(Li0.4La0.6Al0.6)0.1Bi0.8][Mo0.2V0.8]O4 pigments are 96.64 and 93.10% (b* = 77.13, C* = 77.6), respectively. In the acid and alkali resistance test, the color difference values ΔE* of the pigment before and after soaking are less than 5. Finally, the thermal infrared test of the synthetic pigments and commercial pigments on galvanized plates without or with TiO2 was performed. The experimental results show that the temperature difference between the synthetic pigment and commercial bismuth yellow can reach 11 °C. Therefore, it is believed that the synthetic pigment can reflect more heat radiation from sunlight and has better heat insulation performance. The synthetic pigment has higher reflectivity than the commercially available bismuth vanadate pigment, showing its application potential.