Amorphous Mesoporous Magnesium Carbonate as a Functional Support for UV-Blocking Semiconductor Nanoparticles for Cosmetic Applications

Highly porous amorphous mesoporous magnesium carbonate (MMC) with a Brunauer–Emmett–Teller (BET) surface area over 600 m²·g^–1 was evaluated as a micrometer-sized support for TiO₂ and ZnO semiconductor nanoparticles. The resulting MMC-TiO₂-ZnO contained 25 wt % TiO₂ and 25 wt % ZnO incorporated into an MMC structure without blocking the pores as revealed by nitrogen sorption isotherms, scanning electron microscopy, and transmission electron microscopy. In vitro ultraviolet (UV) light-blocking experiments showed that the MMC-TiO₂-ZnO had comparable UV-blocking ability as a TiO₂ and ZnO nanoparticle mixture containing the same amount of semiconductor particles without a support. Amaranth dye degradation studies revealed that MMC was able to diminish the catalytic activity of TiO₂ and ZnO nanoparticles, possibly due to the presence of free carbonate ions in MMC as well as in the dye solution. In summary, this paper demonstrated for the first time that micrometer-sized particles of the recently emerged MMC materials can be used as a support for sun-blocking semiconductor nanoparticles without compromising their UV blocking ability and with significantly lowered photocatalytic activity. When used in a formulation as a support for semiconductor nanoparticles, MMC may also reduce the risk of nanoparticle exposure, and the high porosity of MMC-TiO₂-ZnO may be utilized for the delivery of therapeutic agents to the skin.