A doctoral student in materials science at Technische Universität Darmstadt is making multifunctional nanotubes of gold -- with the help of vitamin C and other harmless substances.
Coffee, apple juice, and vitamin C: things that people ingest every day are experimental material for chemist Eva-Maria Felix. The doctoral student in the research group of Professor Wolfgang Ensinger in the Department of Material Analysis is working on making nanotubes of gold. She precipitates the precious metal from an aqueous solution onto a pretreated film with many tiny channels. The metal on the walls of the channels adopts the shape of nanotubes; the film is then dissolved. The technique itself is not new, but Felix has modified it: "The chemicals that are usually used for this were just too toxic for me." She preferred not to use cyanide, formaldehyde, arsenic and heavy metal salts. She was inspired by a journal article by researchers who achieved silver precipitation using coffee.
Felix also used coffee in her first experiments. She then tested apple juice, followed by vitamin C. This seemed to be the best suited to her because "you never know what's in coffee and apple juice." On the other hand, Vitamin C -- or ascorbic acid -- is available in pure form from chemical stores -- a requirement for reproducible studies. But what does the vitamin have to do with the precipitation of gold? In the human body, vitamin C makes free radicals harmless by transferring electrons to them. "Gold precipitation functions according to the same principle. The only difference is that the vitamin does not take on radicals, but rather gold ions," explains Falk Münch, a postdoctoral researcher and supervisor of Felix' PhD thesis. The gold ions that are dissolved in the precipitation bath are transformed into metallic gold after absorbing electrons.
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