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Using living plants to synthesize metallic nanoparticles.
Metallic
nanoparticles are usually produced by wet chemical methods, often using toxic and flammable substances, or by physical
methods such as evaporation and laser ablation. A group from the Laboratory
for Sustainable Technology, School of Chemical and Biomolecular Engineering,
at the University of Sydney (Australia; edlinks. che.com/7368-534), has been
experimenting with the synthesis of nanoparticles of Cu, Co, Zn, Ni, Ag and
Au, within the cells of living plants - which they call phytosynthesis. They
achieved this by exposing Brassica juncea (Indian mustard), Helianthus
annus (sunflower), and Medicago sativa (alfalfa) to aqueous metal-salt
solutions.
Group
member Andrew Harris says they showed, for the first time, that the size and
shape of the nanoparticles could be coarsely controlled by varying the plants' growth conditions.
The group soaked plant seeds in 5% H202 for 15 min. (to avoid
fungal contamination) and then washed them thrice with deionized water. The
plants were grown under artificial light, for three to four weeks. The plants
were then transferred to Petri plates containing solutions of CoC03,
ZnC12, CuS04·5H20, Ni(N03)2·6H20, AgN03, and KAuC14.
B.
juncea showed the greater
ability to accumulate all of the metals investigated. With all species, the
greater the plant concentration and substrate-metal concentration, the
greater the metal uptake. Also, the metals accumulated far more in the roots
than in the shoots. Ag was most readily accumulated, to a maximum of 9.2% on
a dry weight basis, followed by Au (5%), both with Indian mustard. Co was the
least extracted (1.5 wt.% maximum).
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