Hierarchical micro-/nanostructure of CeO2 mesoporous sphere: From large-scale synthesis to antioxidative application in cosmetics

Cerium oxide nanoparticles (CeO 2 NPs) have attracted great interest recently in the field of cosmetics due to their excellent biomedical properties to treat diseases caused by reactive oxygen species (ROS). However, a realizable synthesis approach for the large-scale synthesis of CeO 2 NPs reaching the quality requirements of cosmetic grade is still in desperate demand. This work reports a robust solvothermal approach for the mass production of self-assembled CeO 2 microsphere (SA CeO 2 ) up to 1000 g at a time. Depending on the concentration of initial precursors, the resulting particle sizes can be precisely tuned to obtain microspherical samples of SA CeO 2 -145 nm, SA CeO 2 -420 nm and SA CeO 2 -680 nm. Typically, the mesoporous SA CeO 2 -420 nm with the largest specific surface area exhibits greatly enhanced number of oxygen vacancies (Ce 3+ cations) proved by X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis. Moreover, Turbiscan stability test reveals the superior physical stability of SA CeO 2 -420 nm suspension based on multiple light scattering technology, which contributes to reduced in-vitro cytotoxicity assessed via MTT viability assay. Therefore, SA CeO 2 -420 nm exhibits excellent antioxidant performance with a high DPPH free radical scavenging ratio of more than 90% at a low concentration below 1 mg/mL. Importantly, SA CeO 2 -420 nm can effectively inhibit the in-vitro release of reactive oxygen species in mitochondria caused by UVB irradiation in HaCaT cells, exerting good antioxidant activity at the cellular level. As a consequence, a significant increase in skin color and brightness can be observed after 28 d of application of the emulsion containing SA CeO 2 -420 nm, demonstrating the potential whitening effect. This work provides a facile and readily scalable synthetic strategy of CeO 2 microsphere and subsequently offers an innovative avenue for their cosmetic application. Large-scale synthesis of micro-/nanostructural CeO 2 mesoporous sphere towards antioxidative application in cosmetics.