(319b) ZnO Nanorods Hermetically Encapsulated By a Nanothin Amorphous SiO2 Coating: Toxicological Profile and Optical Properties

Zinc oxide (ZnO) is a wide-bandgap metal oxide semiconductor that can be excited at room temperature by UV irradiation, and finds applications in a variety of fields and products including paints, pigments, batteries, photocatalysis, foods, to name a few. When in nanometer size range, it may be used in polymer nanocomposites and sunscreens as an efficient UV-filter with high transparency in the visible wavelength range. However, the photocatalytic activity of ZnO causes the degradation of the surrounding polymer rendering it unsuitable for long-term employment. Furthermore, ZnO nanoparticles are highly toxic and may pose risks to the public and the environment. Here, ZnO nanorods are made by scalable flame synthesis [1,2] and are in-situ encapsulated by an amorphous nanothin SiO₂ layer [3,4]. The as-prepared nanoparticles are characterized by electron microscopy (EM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption. The hermetic nature of the SiO₂ coating is evaluated by a detailed dissolution study and the photocatalytic activity is monitored by the decomposition of methylene blue dye. The presence of SiO₂ facilitates the dispersion of these nanorods in relevant solutions. The core ZnO nanorods exhibit the characteristic optical properties as determined by UV/vis and luminescent spectrometry, while the SiO₂ coating eliminates the photocatalytic activity and minimizes the toxicity and genotoxicity to human cells, as illustrated in cellular studies using multiple cell lines. Therefore, these flame-made ZnO nanorods may be safely used as fillers in polymer UV-filter nanocomposites and in sunscreens exhibiting superior performance while mitigating their impact on environmental health.

References

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