Environmental blue CoAl₂O₄ pigment co-doped by Zn²⁺ and Mg²⁺: synthesis, structure and optical properties

ABSTRACT

Nano-sized blue solid solutions Zn_xMg_0.5−xCo_0.5Al₂O₄ (x = 0–0.5) have been synthesised by the Pechini method. Single-phase Zn_xMg_0.5−xCo_0.5Al₂O₄ with crystallite size of ∼40 nm was identified by XRD measurement. The TG-DSC results indicated that the phase formation temperature of Zn_xMg_0.5−xCo_0.5Al₂O₄ increased with the substitution of Zn²⁺/Mg²⁺ → Co²⁺ proceeding. The UV–vis spectra illustrated that the Zn_0.3Mg_0.2Co_0.5Al₂O₄ pigment displayed the most intensive blue colour with the strongest absorbance appearing within the visible region. The FT-IR spectra suggested that the inversion degree of Zn_xMg_0.5−xCo_0.5Al₂O₄ pigment reduces with the increase of Zn²⁺ rather than Mg²⁺, enabling to control the pigment colour by tuning the Zn²⁺ content. The FE-SEM images showed an irregular shaped morphology of Zn_xMg_0.5−xCo_0.5Al₂O₄ crystal, different from the cubic-like morphology of CoAl₂O₄ crystal. The XPS results illustrated that the inversion of pure CoAl₂O₄ pigment is larger than that of Zn_0.3Mg_0.2Co_0.5Al₂O₄. Both Zn_0.2Mg_0.3Co_0.5Al₂O₄ and Zn_0.3Mg_0.2Co_0.5Al₂O₄ show commercial potential in pigments application.

KEYWORDS:

• Absorbance spectroscopy
• solid solutions
• citrate sol–gel method
• blue colour
• inversion degree

Acknowledgements

The authors acknowledge Dechan Angmo for proofreading.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research work is supported by the Fundamental Research Funds for the Central Universities [2016-JL-002].