Tracking Carbonate Phase Formation and Transformation in Nanoporous Amorphous Silica: A Test of Nanoconfinement in Geochemistry
EMSL Project ID
60198
Abstract
Nanoscience—the study of phenomena that occur in the nanoscale dimensional range—is arguably a missing piece in our understanding of the Earth’s subsurface and biogeochemical element cycling. As biogeochemical reactions occur in smaller, more confined spaces, nonlinear deviations from modeled behaviors occur because most current theoretical models are based on bulk thermodynamic and kinetic frameworks and not on the metastable phenomena that occur at the nanoscale (typically 1 to a few 10s of nanometers). The inability to account for differences between bulk and nanoscale molecular behaviors remains a debated cause for mismatch between predictive models and observations made in our environment. However, quantifying nano-domain processes requires thermodynamic and kinetic parameterization of the relationship between nano and bulk behavior, while also considering the complexity of the environment that drives how these nano-processes influence field-scale observations. This limited scope research proposal is dedicated to providing preliminary visual evidence that underscores the need to test the following hypothesis: as pore size decreases, nucleation and growth of otherwise unstable phases predicted by bulk models will occur. The proposal’s success will provide the impetus for systematically duplicating critical inorganic nanoscale processes that occur in subsurface environments across the entire nano-domain in an effort to map transitions in nano- to bulk-dominated behavior as a function of pore size, shape, and time. A controlled experimental approach will parameterize nucleation, growth, and phase transformation processes that occur between biogeochemically relevant aqueous species, e.g., Ca2+ and CO32-, as they interact with nanoporous amorphous silica substrates over short (≤6 hours) and long (14 and 30 days) timescales. Three nanoporous amorphous silica substrates will be purchased to test two nanopore sizes, ~5 nm and 12 nm, and two different pore geometries, hexagonal and cubic. Substrates will be reacted for 6 hours, 14 days, and or 30 days in two different CaCO3 solution concentrations, 1.5 mM and 0.015 mM, to assess phase (trans)formation dependence on CaCO3 concentration. In total 18 substrates will be prepared with the aim of imaging them with EMSL’s vacuum-based TEM instruments equipped with EDS and electron diffraction capabilities that permit the required (sub-)nanometer observations and measurements. Prior to TEM analysis, FIB extractions will be prepared from each of the 18 substrates, also requiring access to EMSL’s Microfluidics and Micromanufacturing Suite for final TEM sample preparations. The proposed experiments will begin to provide key metrics, e.g., phase identification and nucleation, growth, and transformation kinetics, necessary for molecular-scale understanding of the stability, speciation, and interactions among key inorganic elements known to influence organic, nutrient, and contaminant cycling, fate, and transport within subsurface environments. Furthermore, these results, which contribute to a planned five-year phased research program, will also provide metrics critical for DOE BER Earth and Environmental Systems Science Division’s aims to provide “scale-aware predictive understanding” research that captures connections between the molecular scale to field observations of hydro-biogeochemical processes.
Project Details
Project type
Limited Scope
Start Date
2021-09-20
End Date
2021-11-19
Status
Closed
Released Data Link
Team
Principal Investigator