Chemist Eva-Maria Felix uses vitamin C to precipitate gold.
Eva is a doctoral student in the research group of Professor
Wolfgang Ensinger in the Department of Material Analysis is working on making
nanotubes of gold. The technique involves precipitating gold 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; after which the film is
dissolved. Toxic chemicals like cyanide, formaldehyde, arsenic and heavy metal
salts are used in the procedure.
Taking inspiration from a journal article where researchers
had used coffee to achieve silver precipitation, Eva used coffee in her initial
experiments; followed by apple juice. She then tested vitamin C (ascorbic acid)
which seemed to suit her best. Eva said, "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."
Postdoctoral researcher and supervisor of Felix' PhD thesis,
Falk explained the role of vitamin C in gold precipitation- Unlike human body, where
vitamin C makes free radicals harmless by transferring electrons to them, here vitamin
C does not take on radicals, but rather gold ions. The dissolved gold ions are
transformed into metallic gold after absorbing electrons. Harmless chemicals
are required for this process. No expensive devices are required and the
procedure takes place at room temperature without an external power supply,
thus saving energy, and making it a green process. The only thing that is not
green in the procedure is the film (that is used as the template) as it consists
of polycarbonate also made or of polyethylene terephthalate (PET).
The gold nanotubes can be used for building microsensors to
measure hydrogen peroxide, which is known to damage nerve cells and apparently
plays a role in neurodegenerative diseases such as Alzheimer's and Parkinson's.
Scientists are also thinking about using the nanotubes to measure blood sugar. The
green method of production has its advantages here because the components of
such implants should be produced with as few toxic chemicals as possible.