Effects of β-alanine on morphology and optical properties of CoAl2O4 nanopowders as a blue pigment

• CoAl2O4 powders were synthesized via a microwave-assisted combustion solution method.
• Urea, glycine and various weight percentages of β-alanine were used as fuel.
• Powders with single phase spinel structure and 20–30 nm crystallite size were prepared.
• Applying moderate amounts of ß-alanine (5.5 and 35.6 wt.%), resulted in nano pigments with the brightest blue colors.
• ß-alanine enrichment resulted in less agglomerated nano powders.

In this paper, we have synthesized cobalt aluminate (CoAl2O4), nanopowders as blue pigments by the combustion method, which metal nitrates were used as precursor materials and mixture of urea and glycine as fuel. The effect of β-alanine weight percentage as a novel excess fuel on some physical characteristics (e.g. crystallite size and color) of powders has been investigated. The synthesized powders were characterized by means of X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Fourier transform infrared (FT-IR) and Ultraviolet–visible (UV–Vis) spectroscopies. XRD patterns and FT-IR spectra confirmed the formation of pure nanocrystalline CoAl2O4 powders after calcination of the metal-fuel gel precursors at 600 °C for 2 h. Optical band gap of 2.3 eV observed for the prepared powders. The crystallite sizes were estimated of 20–30 nm by means of TEM images and Williamson–Hall method. UV–Vis spectra of the blue metal oxides were characteristics of Co2+ metal ions located in tetrahedral sites. CIE L∗a∗b∗ chromatic coordinates indicated that the bluest color was obtained for β-alanine = 5.5 and 35.6 wt.%.

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