A research team consisting of National Institute for Materials Science (NIMS), Hokkaido University, and Hiroshima University has developed an iron oxide-based ultraviolet (UV)-absorbing powder material by stabilizing normally unstable, colorless, UV-absorbing di-nuclear iron species in porous silica (silicon dioxide). If its performance can be further improved, this material may serve as a viable alternative to potentially carcinogenic titanium dioxide (TiO2), which has been widely used in cosmetics and sunscreens.
TiO2 has been used in a wide variety of products in various applications, including cosmetics, everyday items, food products, medical products, and building materials. However, the European Union classified this substance as a category 2 carcinogen in 2020, causing its use and production to decline and leading France to ban the use of food-grade TiO2. Although Japan hasn’t restricted the use of TiO2, developing alternatives to it is an important national issue considering the size of the Japanese TiO2 market.
A di-nuclear iron species is a type of iron oxide in which a pair of iron atoms are linked by ligands of water molecules or hydroxy groups. This species exhibits higher photocatalytic activity than TiO2 when absorbing UV radiation. This ability separates it from other iron oxides that are used as a red food coloring. Although di-nuclear iron species are commonly found in enzymes and other proteins, they are unstable and difficult to synthesize. Their safe and stable use has long been a focus of research interest. This research team recently succeeded in stabilizing a di-nuclear iron species by embedding it in porous silica powder, thereby restricting it from transforming into a higher-order multinuclear iron species or crystallized iron oxide and reducing its harmful photocatalytic activities. The resulting product is a UV-absorbing white powder material. The team also prepared a sunscreen cream using this material as an active ingredient and found that its performance and stability were comparable to those of the TiO2 materials currently used in sunscreens.
For more information: National Institute for Materials Science
