August 26, 2002
Berkeley Lab Science Beat Berkeley Lab Science Beat
Charting the future of nanogeoscience
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How does a tiny sulfide particle travel from a Chinese factory to California? And how does it react when it gets there? Scientists don't know precisely, which is one of many reasons Berkeley Lab researchers are helping to shape the future of a new field called nanogeoscience.

As the name implies, it's the study of geological processes involving particles no larger than 100 nanometers, meaning in some cases as small as a few atoms across. Such particles play critical roles in carbon sequestration, air pollution, and even the removal of toxins from soil.

But how, and to what extent, remains a mystery. That's because nanoscale particles often don't behave like larger solids. A particle's physical and chemical properties change as it becomes smaller, forcing researchers to use highly sensitive instrumentation such as transmission electron microscopes and synchrotron-based spectroscopy to determine how molecule-sized particles contribute to larger scale phenomena.

And while a small but growing number of scientists probe these poorly understood processes, their work remains largely isolated. Nanogeoscience is a new field, and a researcher who studies how nanoparticles aggregate in soils may not know that other researchers study the analogous process in oceans.

"People who study aerosols don't talk with people who study oceanic particles who don't talk with people who study soil particles," says Glenn Waychunas, a scientist in Berkeley Lab's Earth Sciences Division. "We need to bring them together."

To shepherd the growth of nanogeoscience research, Waychunas and colleagues Jillian Banfield, Hoi-Ying Holman, and Paul Alivisatos are planning a $3 million nanogeoscience program that will encompass Berkeley Lab and UC Berkeley. The program will complement the lab's Molecular Foundry, a national user facility opening in 2006 that will allow researchers to build and test nanoscale devices. And to foster improved communication between nanogeoscientists everywhere, Waychunas envisions a virtual center that electronically links several institutions that conduct innovative research.

Among these inquiries is learning how oceans capture atmospheric carbon, a complex process that plays a key role in our understanding of climate change. Seawater teems with tiny particles that contain nanoscale iron molecules. And iron is crucial in regulating phytoplankton growth, which, in turn, influences the exchange of carbon dioxide between the ocean and atmosphere. So understanding how phytoplankton acquire and use iron will also help explain how oceans capture atmospheric carbon. But researchers don't know where these recently observed nanoscale iron molecules originate, their importance, and how or if organisms use them.

"There is a black hole," says Waychunas. "Oceanographers generally study particles that measure 0.2 microns and larger, which means a lot of nanoscale particles are not examined, particularly with respect to formation mechanisms."

On land, researchers study how nanosized minerals capture toxins such as arsenic, copper, and lead from the soil. Facilitating this process, called soil remediation, is a tricky business. Some toxins weakly adhere to particles through electrostatic forces while others precipitate onto a particle's surface, forming chemical bonds that are more difficult to undo. Even more troublesome is aggregation, in which the precipitated toxin is sandwiched between the grains of a particle. As Waychunas explains, learning how these processes work on the nanoscale could greatly improve the effectiveness of remediation efforts.

Another promising soil remediation strategy links nanogeoscience with biomimetics, an equally new field in which researchers design substances that mimic biological processes. For example, researchers are interested in natural processes in which microbes produce minerals that are highly reactive and therefore ideal components of a toxic uptake system. Taking this a step further, they hope to manipulate microbes into producing nanosized minerals of specific sizes and shapes that most efficiently bind with toxins.

Other research explores the changing characteristics of particles as they become smaller. At the nanoscale, for example, there are many more atoms associated with the surface of a particle than the interior. This intrigues researchers like Waychunas, because most chemical reactions occur on the surface of minerals, large and small. But what's true for a fist-sized chunk of quartz doesn't necessarily translate to a particle only a few molecules across. At this minute size, surface properties can change, meaning the nature of these all-important surface reactions also changes.

Electron Microscope of mineral crystal
A transmission electron microscope image of an anatase (titanium oxide, TiO2) mineral crystal hydrothermally coarsened in dilute hydrochloric acid. The crystal was assembled from smaller nanocrystals via a process called oriented attachment, an alternative to classical growth that occurs on the nanoscale.  

The list continues. Recent research suggests that some airborne nanoparticles are so small they zing through the upper atmosphere for miles without bumping into other particles. How does this affect the spread of air pollution? And other researchers hope to study the nanogeoscience of Martian soil, while still others want to develop computer simulations that model nanogeochemical processes such as aggregation and sorption. Slowly, one study at a time, they're unveiling the role of nanoscale oxide, sulfide, phosphate and silicate particles in global phenomena.

"We need to study the unusual properties of natural materials at the nanoscale," Waychunas says. "And we need to explore how these properties relate to carbon sequestration, plant nutrient transfer, toxic agent entrapment, and many other geochemical cycles."

They're off to a good start: for three days in mid-June, 85 researchers from almost 30 universities, federal agencies, and national labs convened at Berkeley Lab and mapped what is and isn't known in nanogeoscience. In addition to bringing nanogeoscientists under one roof for the first time, the workshop was tasked with helping federal agencies decide how to best facilitate research. The attendees collated important, underfunded research opportunities into a report that will be presented to several federal agencies later this year.

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