ZnO-Based Sunscreen: The Perfect Example To Introduce Nanoparticles in an Undergraduate or High School Chemistry Lab Wanda J. Guedens,* ,†,‡,∥ Monique Reynders, ‡ Heidi Van den Rul, § Ken Elen, †,‡,∥ An Hardy, †,‡,∥ and Marlies K. Van Bael †,‡,∥ † Institute for Materials Research, Chemistry Division, Hasselt University, Campus Diepenbeek, Agoralaan-building D, BE-3590 Diepenbeek, Belgium ‡ Faculty of Sciences, Hasselt University, Campus Diepenbeek, Agoralaan-building D, BE-3590 Diepenbeek, Belgium § Sirris Smart Coating Application Lab, Wetenschapspark 3, BE-3590 Diepenbeek, Belgium ∥ IMEC Division IMOMEC, Agoralaan-building D, BE-3590 Diepenbeek, Belgium * S Supporting Information ABSTRACT: 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. KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Inorganic Chemistry, Laboratory Instruction, Hands-On Learning/Manipulatives, Colloids, Micelles, Nanotechnology, Precipitation/Solubility, Aqueous Solution Chemistry N anoscience and nanotechnology are very interesting fields of study. Because of their impact on tomorrow’s world, it is crucial that these recently developed areas of research are introduced at every level of teaching. 1,2 Especially in high schools, the interdisciplinary character of this area can be exploited. Indeed, within the social environment of high school students, the appealing subject of cosmetics, with nano- sunscreen as an example, is chosen as a framework to get students acquainted with some fundamental properties of nanoparticles and nanoparticle synthesis routes in chemistry lessons. Students learn about skin diseases on short and longer term due to UV sunrays in biology classes, while at the same time, in physics classes, the emission spectrum of sunlight versus that of a tanning bed is studied. The principles of a sunscreen, and nanosunscreen in particular, are described extensively and at a basic level in the NanoSense project, in the activity “Clear Sunscreen: How Light Interacts with Matter”. 3 Depending on the level and the background of the students, the authors strongly suggest to use (parts of) this text as an introductory lesson before adopting the experiment described hereafter. Briefly, a nanosunscreen contains zinc oxide (ZnO) or titanium dioxide (TiO 2 ) nanoparticles as active ingredients. The ability of ZnO and TiO 2 to absorb not only UVB, but also the even more harmful UVA radiation makes these materials particularly interesting for use in recent sunscreens. By using nanoparticles, the sunscreen appears transparent when applied to the skin. Larger, microsized particles scatter more light and leave an undesired, white haze on the skin when used in a sunscreen. Nanoparticles can be manufactured by a variety of routes, commonly classified as wet-chemical, mechanical, form-in- place, or gas-phase synthesis. 4 In wet-chemical processes, solutions of different ions are mixed in defined ratios under controlled external conditions to prepare a large variety of compounds. 5 These kinds of routes can be carried out using simple equipment and are therefore ideally suited for student experiments. A straightforward example of a wet-chemical synthesis route for nanoparticles, applied in this experiment, is microemulsion processing. A microemulsion, defined as a dispersion made of water, oil, and surfactant(s), is an isotropic and thermodynami- cally stable system. In microemulsions, reagents can be encapsulated by a surfactant layer into spheres at the nanoscale, varying approximately from 1 to 100 nm, usually 10−50 nm. 6−9 Published: October 10, 2013 Laboratory Experiment pubs.acs.org/jchemeduc © 2013 American Chemical Society and Division of Chemical Education, Inc. 259 dx.doi.org/10.1021/ed300851a | J. Chem. Educ. 2014, 91, 259−263