Eco-Benign Orange-Hued Pigment Derived from Aluminum-Enriched Biogenous Iron Oxide Sheaths

Inorganic pigments have been widely used due to their low cost of production, strong hiding power, and chemical resistance; nevertheless, they have limited hue width and chromaticity. To eliminate these disadvantages, we herein propose the use of an ingenious biotemplate technique to produce Al-enriched biogenic iron oxide (BIOX) materials. Spectrophotometric color analysis showed that high levels of Al inclusion on heat-treated BIOX samples produced heightened yellowish hues and lightness. The Al-enriched BIOX sheaths exhibited a stable tubular structure and excellent thermal stability of color tones after heating at high temperatures and repetitive heat treatments. Ultrastructural analysis and mechanical destruction experiments revealed that the highly chromatic orange-hue of these pigments are ascribed probably to an ingenious cylindrical nanocomposite architecture composed of putative Fe-included low crystalline Al oxide regions and hematite particles embedded therein. The present work therefore demonstrates that the bioengineered material can serve as an epochal orange-hued inorganic pigment with low toxicity and marked thermostability that should meet large industrial demand.