Nanoscience will change the way we think about the world

The size at which properties and reactivities change can be measured and depends upon the mineral, whether it is a metal, semiconductor, or insulator, and on the property being measured, whether optical, mechanical, or electrical.

Chemical interactions also change. For example, seven nanometer hematite -- a common iron oxide mineral -- catalyzes the oxidation of manganese ions (Mn2+) one to two orders of magnitude faster than does a 37-nanometer hematite crystal, resulting in the rapid formation of the manganese oxide minerals that are important heavy metal sorbants in water and soils.

Thermodynamic considerations in the nano-range are just as critical to predicting whether a biogeochemical reaction will occur. In the smallest particles, surface energies can dominate and dictate which structure of a mineral will be stable. Solubility’s of nanophases are also different than their larger counterparts. “But experiments have shown that nanoparticles may or may not be more soluble than larger particles,” Hochella said.

How nanoparticles influence earth chemistry

An example of the impact of nanoparticles is how they nurture ocean-dwelling phytoplankton, which removes carbon dioxide from the atmosphere. Phytoplankton growth is limited by iron availability, the authors report, citing research by J. Wu, E. Boyle, W. Sunda, L.S. Wen, and B.A. Berquist in two articles from 2001 and 2007. Iron in the ocean is composed of nanocolloids, nanominerals, and mineral nanoparticles, which is supplied by rivers, glaciers, and atmospheric deposition. Nanoscale reactions resulting in the formation of phytoplankton biominerals such as calcium carbonate are also important influences on oceanic and global carbon cycling.

Another example is the movement of harmful heavy metals in the Earth’s critical zone. In ongoing research at the Clark Fork River Superfund Complex in Montana, Hochella’s group discovered a nanocrystalline vernadite-like mineral (a manganese oxyhydroxide) involved in the movement of lead, arsenic, copper, and zinc hundred of miles in the river drainage basin. Radionuclides can also be moved, the review reports. Research by A.P. Novikov (2006) at one of the most contaminated nuclear sites in the world, a nuclear waste reprocessing plant in Mayak, Russian, has shown that plutonium has traveled in local groundwater, carried by nanoparticles of less than 15 nanometers.

In the atmosphere, nanoparticles impact heating and cooling. The characteristics of atmospheric nanoparticles is critical and is now being studied by a large number of scientists. One observation is that such particles act as water drop growth centers, which is critical to cloud formation. The size and density of droplets dictates solar radiation scattering ability and cloud longevity, which influence average global temperatures.

The authors conclude that “The biogeochemical and ecological impacts of natural and synthetic nanomaterials is one of the fastest growing areas of research today, with not only vital scientific, but also large environmental, economic, and political consequences”.

Learn more about the Hochella group at www.geochem.geos.vt.edu/hochella/