Facile synthesis and characterization of 2D kaolin/CoAl 2 O 4 : A novel inorganic pigment with high near-infrared reflectance for thermal insulation

Abstract

Kaolin was chosen as aluminium source to fabricate 2D kaolin/CoAl2O4 blue pigments with high near-infrared (NIR) reflectance by calcination of the precipitated product kaolin/Co2(OH)2CO3. The influence of calcination temperature, ratios of CoCl2·6H2O and kaolin, calcination time and fineness of kaolin on the properties of kaolin/CoAl2O4 were investigated in detail. The formation mechanism with a series of solid-phase reactions was also proposed. The spinel CoAl2O4 with particle size of 30–50 nm was uniformly deposited on the surface of kaolin, and the kaolin/CoAl2O4 pigments prepared under the optimum conditions possessed satisfactory chromatic properties (L* = 38.29, a* = − 9.21, b* = − 38.90, C = 39.98), NIR reflectance (R = 60.18%) and chemically stabilization. The thermal insulation of the kaolin/CoAl2O4 pigments was intuitively evaluated by the pigmented coatings. The kaolin/CoAl2O4 pigmented coatings exhibited excellent thermal-insulating performance compared to CoAl2O4 (ΔT = 4 °C), demonstrating that kaolin/CoAl2O4 pigments might show great potential in serving as cool colorants for the architectural coatings.