Academic journal article The Science Teacher

Shedding Light on the "Science of Small": Exploring Nanoparticles and Energy Conversion

Academic journal article The Science Teacher

Shedding Light on the "Science of Small": Exploring Nanoparticles and Energy Conversion

Article excerpt

Nanoscience development affects almost every discipline of science, engineering, and technology. Not surprisingly, "the science of small" is also finding its way into science classrooms. In general, nano refers to a billionth of a meter--about 1/50,000 the width of a hair follicle. The term nanoparticle usually refers to small materials with a size of between 1 and 100 nanometers (nm). Because nanoparticles are so small, they have a greater surface-area-to-volume ratio, causing them to be more reactive than larger particles and useful for various applications. In this directed inquiry for chemistry students, we introduce contemporary nanoparticle applications that address the Next Generation Science Standards (NGSS Lead States 2013) (see box, p. 32). In the following investigations, students explore titanium oxide (Ti[O.sub.2]) nanoparticles as photocatalysts activated by the energy of ultraviolet (UV) radiation.

[ILLUSTRATION OMITTED]

Ti[O.sub.2] nanoparticles

Research with nanoparticles is a global endeavor. The uses range from silver nanoparticles embedded in fabric to destroy bacteria (Benn and Westerhoff 2008; Erikson 2009; Fountain 2009) to metal grits made of copper tungsten oxide nanoparticles that degrade oil from spills when activated by sunlight (Lee, Clayton, and Gouma 2013). Carbon nanotubes can even target cancer cells (Zhang, Zhang, and Zhang 2011).

Ti[O.sub.2] nanoparticles are photoactive; they use sunlight to split water for hydrogen fuel production. However, Ti[O.sub.2] only absorbs UV radiation and doesn't absorb wavelengths of solar energy within the visible light spectrum--making splitting water using Ti[O.sub.2] for hydrogen generation too inefficient for commercial fuel production. However, Ti[O.sub.2] nanoparticles are useful in solar cell fabrication and self-cleaning glass due to interesting optical and electronic properties.

Engage

To uncover students' prior knowledge of solar energy, we ask them to identify different types of radiation (e.g., solar, gamma, UV). We then discuss the harmful properties of UV radiation, and students identify that it damages skin and can cause cancer, which is why we use sunscreen. We ask them to consider how sunscreen blocks UV radiation, setting the stage to explore Ti[O.sub.2] nanoparticles as photocatalysts and substances found in sunscreens, solar cells, and glass coating.

Explore

Activity I: Ultraviolet radiation and Ti[O.sub.2] nanoparticles: What do they do?

First, we review the chemicals and materials that students use in the lab and remind them of safety procedures and equipment. Students need:

* 0.02 g of silver nitrate (AgN[O.sub.3])

* 120 ml distilled water

* 25 ml > 99% methanol (C[H.sub.3]OH)

* 10 mg of Ti[O.sub.2]

(Safety note: Use gloves and goggles for all activities. AgN[O.sub.3] can irritate skin and stain hands and clothing. Methanol is flammable and an inhalation hazard, so keep it away from flames and use it under a fume hood. Don't look directly into the handheld UV lamp, keep it below eye level, avoid using it on reflective surfaces, and keep hands away from the source. Turn lamps off immediately after use. Mini handheld UV lamps (4 watts, wavelength 365 nm, with intensity 230 [micro]W/c[m.sup.2] ) are available online [see "On the web"].)

Students dissolve 0.02 grams of AgN[O.sub.3] in 100 ml of distilled water. They then combine the 10 mg of Ti[O.sub.2] (solid powder) and 20 ml of distilled water. Working as teams, students mix gently and fill a microcentrifuge tube with 0.5 ml of the AgN[O.sub.3] solution and 0.5 ml C[H.sub.3]OH (Figure 1). They then transfer three drops of the AgN[O.sub.3] and C[H.sub.3]OH solution into the three numbered depressions of a wet well plate.

Students add two drops of the Ti[O.sub.2] solution into depressions 2 and 3, stirring each with a clean toothpick. …

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