ZnO-Based Sunscreen: The Perfect Example To Introduce Nanoparticles in an Undergraduate or High School Chemistry Lab

The experiment described in this article is designed for undergraduates as well as for high school students to help them understand nanoscience in a basic way. The attractive subject of a sunscreen is used to illustrate the properties of nanoparticles. The students prepare particles of Zn(OH) 2 by the same reaction either in a microemulsion, a microemulsion contaminated with acetone, or in an aqueous solution. Hereby it is shown that Zn(OH) 2 has different properties depending on its particle size. Furthermore, the students discover that, due to their higher surface-to-volume ratio, a nanopowder of ZnO dispersed in glycerin absorbs more UV light than the same mass of a micropowder ZnO dispersed in glycerin. Finally, a sunscreen based on a homemade hand cream containing ZnO particles is formulated, and its UV absorbing ability is demonstrated by an uncomplicated procedure. By incorporating more detailed characterization techniques and a more in-depth explanation, these laboratory experiments are also instructive for undergraduate students in the framework of a physical chemistry course.