| Novel Environmentally Friendly (Bi, Ca, Zn, La)VO4 Yellow Pigments |
| Toshiyuki MASUI |
| Osaka University, |
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Inorganic yellow pigments are applied in a wide range of products, such as porcelains, ceramics, inks, and paints. However, several conventional pigments such as chrome yellow (PbCrO4) and cadmium yellow (CdS∙ZnS) contain toxic elements, such as Pb, Cr, and Cd. Because of this fact, we focused on monoclinic bismuth vanadate (BiVO4), which is already known as an environmentally friendly inorganic yellow pigment [1]. The coloring mechanism of monoclinic BiVO4 results from a charge transfer transition from a hybrid orbital of Bi6s and O2p to V3d in the BiVO4 band structure [2]. Therefore, it is expected that the color of BiVO4 can be tuned by introducing other elements into the BiVO4 lattice to control the lattice size, because the extent of the orbital hybridization in the valence band should depend on the interionic distance between Bi3+ and O2−.
Based on this concept, we successfully synthesized Bi1−xLaxVO4 (0 ¡Â x ¡Â 0.15) [3], Bi1−x−yCaxZnyVO4−(x+y)/2 (0 ¡Â x ¡Â 0.10; 0 ¡Â y ¡Â 0.10) [4], and Bi0.90−xCa0.08Zn0.02LaxVO3.95 (0 ¡Â x ¡Â 0.10) [5] solid solutions as environmentally friendly inorganic pigments, and the composition was optimized to produce the most vivid yellow hue. All pigments exhibited brilliant yellow colors. The L* (brightness or darkness), a* (the red–green axis), and b* (the yellow–blue axis) chromatic coordinates of the representative pigments are summarized in Table 1. The b* value corresponding to yellow chromaticity depends on the sample composition. The Bi0.85Ca0.08Zn0.02La0.05VO3.95 pigment has the highest b* value at +93.5, and the most vivid yellow hue was obtained for this sample. Although the yellowness value falls just one step short of that for the toxic PbCrO4 (b* = +96.5) pigment, it is significantly greater than that for the conventional BiVO4 pigment (b* = +76.9). Since BiVO4 is an environmentally friendly inorganic yellow pigment, and Ca, Zn, and La are also nontoxic and safe elements, the Bi0.85Ca0.08Zn0.02La0.05VO3.95 pigment could be an effective alternative to conventional toxic yellow pigments.
Table 1 Chromatic coordinates of the pigments
Samples L* a* b*
Bi0.90La0.10VO4 [3] 89.0 −14.6 +86.6
Bi0.90Ca0.08Zn0.02VO3.95 [4] 87.7 −4.36 +91.6
Bi0.85Ca0.08Zn0.02La0.05VO3.95 [5] 92.8 −6.82 +93.5
Commercially available BiVO4 94.4 −16.7 +76.9
Commercially available PbCrO4 89.9 +1.12 +96.5
References:
[1] E.B. Faulkner and R.J. Schwartz, High performance pigments, 2nd ed., Wiley (2009) pp.7–12.
[2] A. Kudo, K. Omori, and H. Kato, J. Am. Chem. Soc. 121 (1999) 11459.
[3] Wendusu, K. Ikawa, T. Masui, and N. Imanaka, Chem. Lett. 40 (2011) 792.
[4] T. Masui, T. Honda, Wendusu, and N. Imanaka, Dyes Pigm. 99 (2013) 636.
[5] Wendusu, T. Honda, T. Masui, and N. Imanaka, RSC Adv. 3 (2013) 24941.
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Acknowledgements : The present work was supported by the Development of Alternative Technology for Hazardous Chemical Substance and Development of Novel Environment and Human-friendly Inorganic Pigments for Three Primary Colors (FY2010-2014) programs of the Ministry of Economy, Trade and Industry, Japan (METI).
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