Use safe materials for coloring materials containing heavy metals such as mercury, cadmium, and hexavalent chromium, lead pigments, and azo dyes that are suspected to be carcinogenic, which may be harmful to human health and the environment. The conversion to alternative products has become an urgent issue.

　Fine particles of silica, which is an inexhaustible compound on the earth, are used as cosmetics, food additives, etc., and are also present in trace amounts in the living body.Tannic acid obtained from plants and iron tannate formed from iron ions are also used in cosmetics and food additives, and were used as tooth black in Japan in the past.The former is a compound that shows white and the latter is a compound that shows black, but this research group has found that it is possible to obtain coloring materials of various colors by combining these, and to develop colorful pigments made of safe and inexpensive materials. Successful.

　By coating iron tannate around the silica fine particles, gray fine particles having different concentrations can be obtained depending on the amount of iron tannate.After that, when an aggregate of these gray fine particles is formed, it becomes a pigment having a different hue and vividness depending on the aggregated state.It was also found that the color observed from the aggregate varies depending on the size of the silica fine particles used and the amount of iron tannate to be coated.

　This achievement, which succeeded in developing the principle of constructing a material showing vivid and various colors from an inexpensive material with excellent natural harmony, instead of the conventional pigments and dyes whose toxicity is regarded as a problem, is sustainable. It is expected to support a comfortable life.

Paper information:[ACS Sustainable Chemistry & Engineering] Colorful Photonic Pigments Prepared by using Safe Black and White Materials