Glenn A. Waychunas talks with
ScienceWatch.com and answers a few questions about
this month's Emerging Research Front Paper in the field of
Geosciences. The author has also sent along an image
of his work.
Article: Nanoparticulate iron oxide minerals in
soils and sediments: unique properties and contaminant
scavenging mechanisms
Authors: Waychunas,
GA;Kim, CS;Banfield, JF
Journal: NANOPART RES, 7 (4-5): 409-433 OCT 2005
Addresses: Univ Calif Berkeley, Lawrence Berkeley Lab, Div
Earth Sci, Berkeley, CA 94720 USA.
Univ Calif Berkeley, Lawrence Berkeley Lab, Div Earth Sci,
Berkeley, CA 94720 USA.
Univ Calif Berkeley, Dept Earth & Planetary Sci,
Berkeley, CA 94720 USA.
Chapman Univ, Dept Phys Sci, Orange, CA 92866 USA.
Why do you think your paper is highly
cited?
The paper describes modes of toxin/nutrient collection by nanoparticles,
notably by aggregation, which has not been adequately addressed in the
literature. Additionally, new data on the growth of nanogoethite particles
are shown, suggesting that an aggregation mechanism is very important
during early growth. Finally, the paper describes how nanosized natural
mineral phases may differ substantially in properties from their bulk
analogs.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The nanogoethite data is new, and data on metal uptake suggests that the
more disordered structures of the smaller particles alter the precise
nature of binding to these nanoparticles compared to larger sized
particles.
Would you summarize the significance of your paper in
layman's terms?
Natural nanoparticles, especially of reactive compositions such as iron
oxides and hydroxides, may play a disproportionally important role in
contaminant transport and sequestration in the environment. This is due to
structural and chemical variations in the nanoparticles at very small sizes
(0-20 nm) that are fundamentally different from larger crystallites and
mineral surfaces, and to the incorporation of contaminants into
nanoparticles during aggregation.
It is also shown that aggregation itself may be an important aspect of
early nanoparticle growth, in competition with classical growth in an "atom
by atom" mode. These considerations suggest that metal or anion contaminant
transport (e.g. of arsenic, mercury, or copper) may be markedly changed if
reactive nanoparticles are present or forming in the same environmental
systems.
How did you become involved in this research and were
any particular problems encountered along the way?
We have an interactive group of principal investigators at UC Berkeley and
at Lawrence Berkeley National Laboratory who collaborate on nanoscience
projects. We call our laboratory the "Berkeley Nanogeoscience Center" and
investigations focus on the properties and reactivity of naturally
occurring nanoparticles.
Where do you see your research leading in the
future?
One of our main aims is to interpret the atomic-scale structural aspects of
natural nanoparticles, especially at the surfaces, which give rise to
altered reactivity and physical properties. This is an important research
area in all of nanoscience, except that most engineered nanoparticles have
surfaces terminated by capping ligands, and are generally well-defined.
With natural nanoparticles, the surfaces are not capped and vary with
degree of crystallinity and growth conditions, and hence present a rich and
variable field of reactive sites for interactions with natural agents, such
as contaminants.
Study of this inherent complexity could lead to improved synthetic
preparations of nanoparticles with precisely tuned properties, in chemical
coherence with the natural environment. We have also found, and are
continuing to study, the dramatic changes in water structure at
nanoparticle surfaces observed in simulations.
Do you foresee any social or political implications for
your research?
Tuned nanoparticle structure, and thus properties, may be very important in
environmental remediation efforts. Efforts now underway to develop
large-scale carbon sequestration methodology may also involve very
specialized mineral nanoparticles to react with and precipitate high
CO2 brine solutions. These types of applications can have
potentially great social and political implications.
Glenn Waychunas, Ph.D.
Senior Staff Scientist
Group Leader, Molecular Geochemistry and Nanogeoscience
Earth Sciences Division
Geochemistry Department
Lawrence Berkeley National Laboratory
Berkeley, CA, USA
Nanogoethite particles formed from solution showing internal structural
variations consistent with formation from smaller nanoparticles (about 5 nm
diameters) via a process called oriented aggregation or OA. In this form of
aggregation, the crystallites assemble with consistent crystallographic
orientations to form a new larger single crystal. This type of formation
process appears to compete with classical “layer by layer”
growth in some cases, and leads to changes in the kinetics of growth in the
nanoparticle size regime. During OA, or during aggregation without specific
orientation, contaminants in the growth solution can be internally captured
by the growing nanoparticles. Such encapsulation allows distant transport
of contaminants compared to ordinary sorption processes. Photo by
Christopher Kim (Chapman University). Taken at the National Center for
Electron Microscopy (NCEM) LBNL.
Why do you think your paper is highly
cited?
