Berkeley Nanogeoscience Research Program

Biogeochemistry

Nanoparticulate iron oxyhydroxide controls on aqueous redox chemistry and microbial species distribution and activity in natural environments.
Natural microbial communities are likely to include organism types with the range of genomic potential needed to profit from the expected suite of electron accepting minerals encountered in their habitats. We predict that redox potential is a mineral characteristic key to strain selection, and we will experimentally adjust the redox potential of electrodes coated with iron oxyhydroxide nanoparticles and test for reproducible patterns of organism response. We hypothesize that we can drive selection for the strain with cytochromes best optimized to use the available mineral substrate. The biochemical basis for selection will be investigated through identification of protein variants involved in energy metabolism and protein-nanomaterial interactions.

For more information, contact Jill Banfield. This project is supported by DOE BES (Geochemistry).

Structure and Reactivity of Nanoparticle and Bulk Mineral Interfaces

Coupled Diffusion and Adsorption Processes within Aggregates of Iron Oxyhydroxide Nanoparticles
The water-mineral interface is the site for important chemical cycles in the environment, including the adsorption of nutrients and contaminants, surface hosted catalysis, and direct redox reactions between minerals and aqueous ions. In many natural settings, particle aggregation reduces the amount and the accessibility of potentially reactive surfaces. Thus, the rates of geochemically relevant processes are frequently controlled by the mobility of aqueous inorganic or organic species within complex, nanoporous aggregates.

We are using small angle-x-ray scattering combined with computational methods to generate 3D models of nanoparticle aggregates (see Figure). We have found that aggregate morphology varies considerably with aggregation pathway (such as pH variation, drying or freezing) and that pore morphology exerts considerable influence on the extent and kinetics of the adsorption and release of aqueous copper ions. We are combining molecular dynamics and lattice Boltzmann simulation methods to provide insight into the physical and chemical controls on interfacial processes within nanoparticle aggregates.

For more information, contact Ben Gilbert. This project is supported by DOE BES (Geochemistry).

Molecular Structure and Processes and Mineral-Water Interfaces.
Structural studies of hydrated mineral surfaces have indicated significant deviations from the bulk-terminated structure often assumed in surface models.  Some of these differences are simple bond-length relaxations, but others reflect new degrees of surface protonation and organization of overlying water molecules (goethite), or changes in surface site occupations associated with altered chemical reactivity (hematite). In the proposed studies we seek to extend our past work to additional important natural mineral surfaces (goethite, diaspore), to surfaces with sorbed inorganic and organic species of differing chemical and physical properties, and to undersaturated conditions where precipitation may be readily initiated.

For more information, contact Glenn Waychunas. This project is supported by DOE BES (Geochemistry).

Environmental and Human Health Impacts of Engineered Nanomaterials

While it is now recognized that the manufacture of nanomaterials may represent unique risks to humans and the environment, the field of nanotoxicology remains at a nascent state. Inorganic nanowires have received very little attention but there is a growing expectation that these materials may have a widespread technological use.

In collaboration with Chris Vulpe and the Berkeley COINS Center we are studying the environmental impacts and biological toxicity of nanowires, initially focusing on silver nanowires.

Ultrafast Science

Imaging Electronic and Atomic Redistribution during Redox Reactions at Surfaces
Reactions that occur on timescales of less than one millionth of a second are central to biogeochemical processes that shape the Earth's surface. For example, the cycles of redox active elements such as iron, sulfur, and oxygen are tightly coupled to the carbon cycle in both marine and terrestrial environments. Many of the pathways involve transfer of multiple electrons between aqueous ions and solids, and thus occur at hydrated mineral surfaces. However, the speed of the fundamental chemical steps render them inaccessible to conventional study. We propose to develop a suite of ultra-fast x-ray methods to visualize the coupled electronic and molecular steps that occur during redox transformations at the water-mineral interface and to quantify the rates of intrinsic steps. We will focus first on the oxidation of  pyrite (FeS2), a reaction central to acid mine drainage formation and biohydrometallurgy, and the reductive dissolution of iron oxide (Fe2O3), a process central to bioremediation of radionuclide-contaminated sites.

We will image the time evolution of surface electron density distributions, surface structure, and local chemical speciation as the surfaces react. The experiments will make use of nanoparticles of discreet sizes to determine the effect of particle size on reaction rates and mechanisms. The results of this work will advance basic understanding of how electrons are transferred into and out of solids and may find application in both environmental remediation and technology development.

For more information, contact Glenn Waychunas. This project is supported by the DOE Chemical Imaging.

Nanoparticle Growth

This task will study the growth of nanoparticles in neutralized metal-contaminated acid mine drainage (AMD) solutions to describe, at the atomic level, the processes by which nanoparticles form, identify the impacts of impurities on the growth mechanisms, and determine how interacting and competing processes determine the fate of contaminants. The research objectives will be accomplished by integrating results of experiments, molecular-scale characterization, and simulations.