Synthesis and characterization of Co1-xCaxAl2O4 composite blue nano-pigments by the polyacrylamide gel method

•Blue nano-pigments of Co1-xCaxAl2O4 were synthesized by the polyacrylamide gel method.•It was found the Ca2+ can improve the degree of color and brightness of pigments.•Co1-xCaxAl2O4 pigments synthesized would be a new candidates for cool pigments.

Blue nano-pigments of Co1-xCaxAl2O4 (x = 0.1, 0.2, 0.4, 0.6, and 0.8) were synthesized by the polyacrylamide gel method. The obtained powders were characterized by XRD, SEM, colorimetry and UV-vis. The XRD patterns indicated the characteristic peaks were attributed to the CoAl2O4 and CaAl2O4 phases with a good crystallinity. The crystallite sizes decreased with the increase of calcium content. The colorimetric data revealed that the increases of blue intensity and bright component originated from the enrichment of calcium. When the content of Co was 0.2 (sample P5), the pigment showed the bluest and brightest color. The UV-vis absorption spectra in the range of 430-670 nm decreased with the increase of calcium content thus causing the pigments became brighter and bluer. Incorporation of calcium elements into the CoAl2O4 reduced the production costs and also minimized the damage to the environment. These facts show the potential of the obtained powders for cool coatings.