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Rustproof tinplate material provides safe UV protection

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image: A research team led by NIMS, Hokkaido University and Hiroshima University has successfully developed a white powder material that absorbs UV while reducing its harmful photocatalytic activities. This was achieved by mixing commercially available porous silica and a solution containing a mononuclear iron species ([Fe(H2O)6]3+). The team then mixed this powdered material with a natural oil to create a paste, evaluated its sunscreen performance and found it to be equivalent to TiO2 in performance and stability. Analysis conducted by Hokkaido University confirmed that the UV absorbing ability of the powder is attributed to the dinuclear iron species immobilized in the silica pores.
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Credit: Yusuke Ide National Institute of Materials Science [email protected]

A research team consisting of NIMS, Hokkaido University and Hiroshima University has developed an ultraviolet (UV) absorbing powder material based on iron oxide by stabilizing iron species normally unstable, colorless, UV-absorbing dinuclears (iron atoms are shown as purple spheres in the figure below) 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 (for example, as a white pigment, in UV protection (mainly by scattering and neutralizing UV radiation) and as a photocatalyst), including cosmetics, articles of all days, food products, medical products and building materials. However, the European Union classified this substance as a category 2 carcinogen in 2020, leading to a drop in its use and production and leading France to ban the use of food-grade TiO.2. Although Japan has not restricted the use of TiO2the development of alternatives is an important national issue given the size of Japanese TiO2 market.

A dinuclear 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 rays. This ability separates it from other iron oxides that are used as red food coloring. Although dinuclear 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. This research team recently succeeded in stabilizing a dinuclear iron species by incorporating it into porous silica powder, thus preventing it from transforming into a higher order multinuclear iron species or crystallized iron oxide and by reducing its harmful photocatalytic activities. The resulting product is a white UV absorbing powder material. The team also prepared a sunscreen using this material as an active ingredient and found that its performance and stability were comparable to TiO.2 materials currently used in sunscreens.

This research team has developed a procedure to synthesize the white powder material capable of absorbing and neutralizing UV radiation using ingredients that are safer than TiO2. This material can potentially be used to develop new cosmetics and sunscreens. Additionally, the microporous structure of silica, which is used to stabilize dinuclear iron species, can be modified to maximize photocatalytic activities of iron species. This approach can be applied to the development of photocatalysts that can be used in air purifiers and other technologies. The team will investigate this possibility.

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This project was carried out by a research team led by Yusuke Ide (Senior Researcher, International Center for Nanoarchitectural Materials, NIMS), Shinya Mine (Postdoctoral Researcher, Institute of Catalysis (ICAT), Hokkaido University (HU)), Takashi Toyao (Assistant Professor, ICAT, HU), Ken-ichi Shimizu (Professor, ICAT, HU) and Nao Tsunoji (Assistant Professor, Graduate School of Advanced Science and Engineering, Hiroshima University). This work was supported by the JSPS Grants for Scientific Research (Grant Number: 21H02034).


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