A new video produced by the American Chemical Society features current research from the lab of assistant professor Tina Salguero. The video, part of the ACS Publications "Breakthrough Science" series, focuses on a recently published communication in the Journal of the American Chemical Society (DOI: 10.1021/ja310587c) highlighting the synthesis of nanosheets of calcium copper tetrasilicate (CaCuSi4O10), the key component of a pigment known as Egyptian blue that has been manufactured since the third millennium BC. The work has received much press from major scientific news outlets, such as Scientific American, C&EN, the Materials Research Society, and even The History Channel and Archaeology magazine. The idea to study this material was inspired by a television program about ancient Chinese pigments like Han purple (BaCuSi2O6), a material that recently attracted the attention of physicists for its ability to undergo a 3D to 2D transition that gives the material unique magnetic properties. Chris Barrett, a former post-doc in the Salguero lab, happened upon this show one night and wondered whether the “dimensional reduction” of related silicates would afford additional novel properties. This project was taken up by Darrah Johnson-McDaniel, a second-year chemistry graduate student. At first she tried the standard strategy of intercalating small organic molecules into CaCuSi4O10 crystals to exfoliate the bulk material into 2D nanosheets. In the control experiment, she stirred the material in just 80 °C water—and found that the pigment had delaminated! The discovery definitely was surprising. “We got something completely different than what we were expecting,” she said. Egyptian blue emits in the near-IR range (910 nm), which is unusual for materials not containing rare earth elements. The unique emission profile opens up a wide array of applications in the field of telecommunications, security ink, and non-invasive medical imaging. To demonstrate the ease of incorporating the pigment into an ink, second-year chemistry graduate student Asma Sharafi inkjet printed a pattern of squares with the Egyptian blue nanosheets. To use the material for security ink, Darrah suggested, all you would need to do is “print it on money and see if it emits in the near-IR. It would be a simple check. You would just need a camera and a filter.” Egyptian blue could also find use in non-invasive medical imaging because it emits in a region where tissues and muscles do not, and thus won’t interfere with imaging. This remarkably simple means of creating nanosheets has encouraged the group to look into similar materials, such as gillespite (BaFeSi4O10) and other silicates. If exfoliation is as simple as with Egyptian blue, the group may find valuable new sources of nanomaterials from relatively inexpensive and common minerals.
