Although a significant fraction of naturally-occurring inorganic phases have been identified as nano-sized clusters, crystals, particles and aggregates, apparent gaps remain in our knowledge of how these naturally-occurring nanomaterials are formed and interact with other biogeochemical components such as soluble species and microorganisms in nature. Our mission for years has been to leverage the interdisciplinary thinking in nanogeoscience to advance the understanding of fundamental (bio)geochemical processes involving naturally-occurring nanoparticles on Earth, particularly those governing the distribution and cycling of elements, and the transfer of electrons and energy between minerals, other inorganic/organic Earth components, and also associated microorganisms.
As an important outcome of our most recent BES Geosciences contract, we have illuminated the mechanisms involved in the biological versus abiotic formation of ZnS nanocrystals that were repeatedly detected in stormwater ponds, abandoned mines, wetlands, and wastewater treatment plants. And our work nicely explains the exclusive occurrence of ZnS as nanoscale phases in these various natural and engineered settings. Further, we have also revealed that the crystal structures of the biogenic and abiogenic ZnS are highly susceptible to the co-existence of other metals like Cu2+ in their formation pathways. Altogether these findings have opened the discussion about the origin, formation mechanisms, structure and reactivity of nanominerals in a much broader sense and have provided us with a kernel that we wish to expand upon aggressively in the next three-year funding increment. Specifically, we wish to widen and deepen our investigations regarding biogenic (using sulfate-reducing bacteria to stimulate sulfide production) versus abiogenic formation of nanominerals by systematically examining the iron-sulfide and mixed metal-sulfide (i.e., Zn-Fe, Fe-Cu, and Fe-Co sulfide) systems. This knowledge-space has never been explored before, by any group, yet we believe it to be a fundamental Earth process of great importance. There are three major goals that we intend to achieve through this proposed work: 1) to understand nanoparticle formation for several mix-metal sulfide nanophases via bacterial sulfate-reducing versus abiotic, ligand-free pathways; 2) to elucidate their interfacial reactivity via measurement of redox activity and photocatalysis efficiency; and 3) to relate our results to what we see in the field, the combination of which will allow us to delineate the role of these phases in nature.
We have been focusing our research on metal-sulfide and mix-metal sulfide nanominerals for various reasons, mostly due to their importance in the biogeochemical cycling of sulfur, contaminant geochemistry, resource recovery, environmental toxicology, and microbial ecology. This line of research will be highly impactful considering the exclusive co-existence of multiple metallic elements in naturally-occurring sulfide nanophases as well as the dramatic effect on the structural and electronic properties of these nanomaterials such as band gaps and photosensitivity with the co-existence of other metals.
The work will be carried out with the backing from Virginia Tech’s National Center for Earth and Environmental Nanotechnology Infrastructure (NanoEarth). This NSF- and DOE-supported National Center was founded and is directed by Dr. Hochella, PI of this proposal. It is a core member of the NSF-funded National Nanotechnology Coordinated Infrastructure (NNCI), and the only center in the NNCI network that is dedicated to Earth and environmental science. Additionally, NanoEarth is partnered with the Environmental Molecular Sciences Laboratory (EMSL) of Pacific Northwest National Laboratory
