Synthesis and characterization of Co sub(1-x)Zn sub(x)Cr sub(2-y)Al sub( y)O sub(4) as a near-infrared reflective color tunable nano-pigment

A series of near-infrared reflective nano-pigments based on Co sub(1-x)Zn sub(x)Cr sub(2-y)Al sub( y)O sub(4) (x = 0-1 and y = 0-2) have been synthesized via Pechini-type sol-gel method. Comprehensive analyses were carried out to characterize the resulting powders including X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared analysis and UV-Vis-NIR spectrophotometry. The colors of spinel structures were directly related to the occupation of tetrahedral and octahedral positions by the chromophores. The results revealed that the substitution of Zn super(2+) for Co super(2+) ions in the tetrahedral positions, and Al super(3+) for Cr super(3+) ions in the octahedral positions of CoCr sub(2)O sub(4) not only reduce the cost but also increased near-infrared solar reflectance (R* > 43%). Furthermore, the coatings colored with the optimum pigments possessed high near-infrared solar reflectance (R* > 50%) with respect to the conventional coatings. These facts express the potential of the pigments to be employed in cool coatings.