SB: Recommended: "No fairy tale: Researchers spin straw into gold"

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SB: Straw - more wonderful uses

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Headline:  No fairy tale: Researchers spin straw into gold
Byline:  Peter N. Spotts Staff writer of The Christian Science Monitor
Date: 08/29/2002

Rumpelstiltskin, the fairy-tale rogue who spun straw into gold, has 
nothing on Miguel Yacaman and Jorge Gardea-Torresdey.

The two University of Texas researchers have developed a way to draw 
gold from wheat, alfalfa, or - best of all - oats.

No spinning wheel required. In this day and age, a simple solvent will 
suffice to turn homely vegetation into a source of precious metals.

But if you're thinking of quitting the day job and buying an alfalfa 
farm, don't be too hasty. The quantities of gold at stake won't quickly 
cover the cost of a harvesting combine.

The yields, in fact, are microscopic. The gold appears as particles 
mere billionths of a meter wide.

But the duo holds that their approach - which takes advantage of 
plants' metal-absorbing abilities -- could provide a cheap way to 
"mine" gold from soils, with the plants supplying the gold in forms 
tailor-made for use in the burgeoning field of nanotechnology.

The work represents the first time researchers have reported that 
living plants form these gold micro-nuggets, opening "exciting new ways 
to fabricate nanoparticles," according to Dr. Gardea-Torresdey, who 
heads the chemistry department at the University of Texas at El Paso.

He notes that current approaches to making gold nanoparticles, now used 
as tags for studying cellular processes in biology and coveted for use 
as electrical contacts in nanoelectronic circuits, are expensive and 
involve chemical processes that generate pollution.

The use of plants, he holds, "is both cost-effective and 
environmentally friendly."

Researchers have known for years that plants take up metals. Plants' 
abilities to absorb all sorts of toxic compounds have led to their use 
as biological vacuum cleaners on sites tainted with pollutants ranging 
from arsenic, TNT, and zinc to radioactive cesium. By some estimated, 
phytoremediation could become a $214 million to $370 million business 
within the next three years.

Indeed, the key piece in the gold-from-alfalfa puzzle fell into place 
during a hazardous-waste clean-up effort outside Mexico City, according 
to Dr. Yacaman, a chemical engineering professor who came to Austin 
from Mexico two years ago. While in Mexico serving as director of the 
physics institute at the National Autonomous University of Mexico, 
Yacaman teamed up with Gardea-Torresdey to use plants to clean up the 
site, heavily contaminated with chromium.

When the two analyzed the plants, "the tremendous surprise was that the 
metal was not dispersed in the plant as we assumed, but was 
precipitated in the plant as clusters of nanoparticles, exactly the 
same ones called quantum dots in the electronics industry," Yacaman 
says.

What started out as a plant-based pollution clean-up project quickly 
turned into a nanotechnology research project, he adds. The two 
scientists and their colleagues also knew that plants had been used to 
prospect for gold.

In the tropics, for example, researchers from Australia, Canada, and 
Papua New Guinea found that gold concentrations in plants could serve 
as effective stand-ins for direct soil samples in efforts to find new 
gold deposits. Plants were particularly effective where soils had been 
covered by dust and ash from volcanic eruptions and so couldn't be 
tested directly.

The question was whether easily grown crop plants could also sequester 
gold, and in nanoparticle form.

The team started with alfalfa, germinating seeds in an artificial, 
gold-rich medium. Using powerful x-ray and electron microscopes, they 
not only struck gold in the alfalfa shoots, but found that they formed 
the nanoparticles they were looking for.

Extracting the metals presents no problem, Yacaman says. In essence, 
"you can easily dissolve the organic material," leaving the gold intact.

Although initial experiments showed that the gold particles formed in 
random shapes, Yacaman says it appears that by changing the acidity of 
the growing medium, the shapes become more uniform.

Since it first reported its work in the American Chemical Society's 
Nano Letters in January, the team has worked with other metals, using 
plants to manufacture nanoparticles of silver, Europium, palladium, and 
iron.

"We are now ... fabricating a platinum ion that could be used for 
magnetic recording," Yacaman says.

For industrial-scale production, the team holds that the plants can be 
grown indoors in gold-enriched soils, or they can be "farmed" at 
abandoned gold mines.

In addition, they've tested the approach on wheat and oats, finding 
that oats are much more efficient at taking up gold than alfalfa.




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