Facile synthesis and characterization of 2D kaolin/CoAl2O4: A novel inorganic pigment with high near-infrared reflectance for thermal insulation

Abstract Kaolin was chosen as aluminium source to fabricate 2D kaolin/CoAl 2 O 4 blue pigments with high near-infrared (NIR) reflectance by calcination of the precipitated product kaolin/Co 2 (OH) 2 CO 3 . The influence of calcination temperature, ratios of CoCl 2 ·6H 2 O and kaolin, calcination time and fineness of kaolin on the properties of kaolin/CoAl 2 O 4 were investigated in detail. The formation mechanism with a series of solid-phase reactions was also proposed. The spinel CoAl 2 O 4 with particle size of 30–50 nm was uniformly deposited on the surface of kaolin, and the kaolin/CoAl 2 O 4 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/CoAl 2 O 4 pigments was intuitively evaluated by the pigmented coatings. The kaolin/CoAl 2 O 4 pigmented coatings exhibited excellent thermal-insulating performance compared to CoAl 2 O 4 (Δ T  = 4 °C), demonstrating that kaolin/CoAl 2 O 4 pigments might show great potential in serving as cool colorants for the architectural coatings.