Assessment of Cell Toxicity and Oxidation Catalytic Activity of Nanosized Zinc-doped Ceria UV Filter

S. Kurajica, K. Mužina, S. Keser, G. Dražić and I. K. Munda

Abstract
The abundance of cerium in natural resources, its ability to absorb UV light while being transparent to visible light, as well as low photocatalytic activity make ceria (CeO2) a promising candidate for UV filter material in sunscreens. Doping with different elements can further decrease ceria catalytic and photocatalytic activity, thus preventing the degradation of other sunscreen ingredients. In this work, pure and zinc-doped ceria nanoparticles were prepared by a simple and environmentally benign hydrothermal synthesis, and characterized using various techniques. Fine ceria and doped ceria nanoparticles with particle sizes of 6.1±0.9 and 4.2±0.4 nm were prepared. In both samples, cubic ceria was the only crystalline phase, but the homogeneous distribution of zinc in the doped sample was confirmed by energy dispersive X-ray spectrometry. Nanoparticles exhibited transparency in the visible region and absorbance in the UV region with band gap of 3.23 to 3.14 eV for pure and doped sample, respectively. The oxidation stability time, determined through Castor oil oxidation process, was 23 hours for the pure and 15 hours for the doped sample, which is quite satisfactory. In vitro cytotoxicity study showed that the prepared nanoparticles were well tolerated by human skin keratinocytes (HaCaT cell line) with no significant differences in skin cells viability. However, further investigations on in vivo systems are necessary to reach a firm conclusion regarding the toxicity of ceria and doped ceria nanoparticles, and other potential dopants should be considered for improvement of ceria properties.

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Keywords
doped ceria, hydrothermal synthesis, HaCaT cell line, cytotoxicity