Nanoparticles in Sunscreens

Titanium dioxide and zinc oxide are currently used for sunscreens because they absorb and scatter light. University of Tennessee, Knoxville, scientists have found that nanoparticles found in ivy may protect skin from UV radiation at least four times better.

A yellowish material is secreted by the ivy to aid it in clinging to surfaces. Nanoparticles within this material create the ability for the vine leaves to hold almost 2 million more times than its weight as well as provide the ability to absorb and disperse light due to their large surface-to-volume ratio. Sunscreens made with ivy nanoparticles would probably not need to be re-applied after swimming because the nanoparticles are more adhesive, and, while metal-based sunscreens give the skin a white tinge, the ivy nanoparticles are virtually invisible.

The study indicates that ivy nanoparticles are less toxic to mammalian cells than small-scale metal oxides, have a limited potential to penetrate through human skin, and are easily biodegradable.

Reference:
University of Tennessee at Knoxville (2010, July 19). Nanoparticles in English ivy may hold the key to making sunscreen safer and more effective. ScienceDaily. Retrieved July 22, 2010, from http://www.sciencedaily.com­ /releases/2010/07/100719162955.htm

Study Questions

1. Write the formula for titanium dioxide and for zinc oxide.
2. Give the oxidation state (number) for titanium and zinc in the compounds above.
3. What is a nanoparticle?
4. Explain the term surface-to-volume ratio.
5. Why do nanoparticles have a large surface-to-volume ratio?
6. How is the scattering of light affected by differences in surface-to-volume ratio?
7. Why are titanium dioxide and zinc oxide the preferred metal oxides for use in sunscreens?