Learn more about nanoparticles with hands-on models

An Oregon chemistry teacher has developed an innovative way to teach nanoscience using 3D printed models that make the invisible visible.

Nanoparticles are super small, their size can be a nanometer or a billionth of a meter, and they are very interesting to materials scientists due to their unique physical and chemical properties. They cannot be seen with the naked eye and to see them you need a very special electron microscope.

In fact, advances in imaging technology in the 1990s and early 2000s made the field of nanoscience possible, says Anne Bentley, a professor in the Department of Chemistry at Lewis & Clark College in Portland, Oregon.

“I think a lot of chemistry is outside the realm of what people can get their hands on,” he says. “You can get evidence of what’s going on, but you’re still investigating something that’s on a scale too small for your eyes to see. “Anything you can do to expand it is helpful.”

So Bentley did just that, creating 3D models of the simplest geometric shapes that form nanoparticles. She published instructions for creating these models, either with paper or with 3D printing materials, as part of an article she co-authored in the Journal of Chemical Education titled “A Primer on Lattice Planes, Crystal Facets, and Nanoparticle Shape Control.”

A handbook for students of materials chemistry

Nanoparticles have different geometric shapes and are crystalline, meaning they are made up of atoms arranged in a pattern that repeats in three dimensions. The shapes have flat surfaces, called planes or facets, similar to the cuts of a gemstone. The arrangement of atoms on these crystalline surfaces influences the material’s special properties, explains Bentley.

“Shapes are derived from the arrangement of atoms,” he explains. “The motivation to create different shapes really comes from the arrangement of the atoms when the material is cut in different ways at different crystal levels.”

In the article, Bentley focuses on low index shapes, which he describes as the three easiest ways to cut the structure.

“There are many more complex ways to cut it, but these are the three basic ones: six, eight or twelve sides: cube, octahedron or rhombic dodecahedron. “It was a natural choice to focus on these three for the article.”

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Transform a “jumble of numbers” into shapes

“Nanoscience is a topic that sits in the curriculum between chemistry and physics, but also between undergraduate and postgraduate research,” says Bentley. “It is important for aspiring materials chemists to have a basic understanding of crystal planes, facets and growth directions. You also need to understand the three-digit notation system used to index these attributes, called Miller indices. Otherwise, this system can seem like a mysterious jumble of numbers.”

He believed it was important to provide a knowledge base in an accessible format that could help educators navigate this important and growing field. Although computer simulation programs can be used to digitally create more complex structures than 3D printed models, Bentley believes there are benefits to being able to hold the models in your hands.

“I like things I can look at and think about,” he says, adding that 3D models are particularly useful for developing an understanding of this key topic in nanoscience.

Growing gold particles to convert carbon dioxide

In Bentley’s lab, she and her students manipulate gold atoms in liquid vials to control the shape of the nanoparticles.

“You have to create the right conditions and temperatures, an environment that is conducive to growth in some way,” he explains.

Bentley studies gold nanoparticles that are characterized by their catalytic properties, or the ability to speed up chemical reactions. The way the material is cut reveals different patterns of atoms, he explains. Previous research has found that a particular form of gold nanoparticles, the twelve-sided rhombic dodecahedron, is most effective at converting carbon dioxide into combustible materials.

“It’s like recycling,” Bentley says. “This form of nanoparticle allows researchers to not only remove carbon dioxide from the atmosphere, but also convert it back into some kind of usable fuel.” “So if we can grow particles that only have this facet, that would be a real advantage. “


An introduction to lattice planes, crystal facets, and control of nanoparticle shape

Photo: Stephen Mercier/Lewis & Clark College

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