Directorate-General for Health and Food Safety
3. What are the properties of ZnO nanoparticles?
Nanoparticles are chemically similar to other preparations of the same material. Their physical, chemical and biological behaviour may differ in some respects, mainly because of their small size and the large surface area this yields for the same amount of material. Chemical catalysts used in industry, for example, are usually finely divided because this exposes a larger surface area to the chemical reactants affected by the catalyst. Some nanoparticles may also cause unexpected effects in living cells because their sizes are similar to important biological molecules, or parts of them, or because they can pass through barriers which block passage of larger particles.
Zinc oxide nanoparticles preparations used in sunscreens have been tested extensively to assess their physical and chemical properties. Nanoparticles manufactured by different methods were found to be broadly similar, and most of their properties apart from size distribution match those of larger particles. They have the same crystal structure and the particles assume the same range of shapes. In the particular case of nanomaterials used in cosmetics, both solubility and dissolution rates need to be considered. It has been shown that the nano form of ZnO has a higher dissolution rate than bulk ZnO.
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