Synthesis and characterization of Co1−xZnxCr2−yAlyO4 as a near-infrared reflective color tunable nano-pigment

Abstract

A series of near-infrared reflective nano-pigments based on Co1−xZnxCr2−yAlyO4 (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 Zn2+ for Co2+ ions in the tetrahedral positions, and Al3+ for Cr3+ ions in the octahedral positions of CoCr2O4 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.