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Huifang Xu - Research Activities


Current Research Activities in Nanogeoscience Group


Right: Fig1A [110] zone-axis Z-contrast image of silicon (left); High-resolution TEM image of a partially weathered amphibole with domains of wide chains (precursor of smectite) (right).

♦ Atomic resolution chemical imaging of mineral structures and defects: One of my long-term research goal is to investigate interface structure and defects in minerals and crystalline materials in order to understand formation/evolution history of minerals and physical and chemical properties of materials. A state-of-the-art field emission-gun scanning transmission electron microscope and high-resolution TEM (FEI Titan‑80‑200) equipped with cutting edge technology spherical aberration correction for electromagnetic lens (supported by UW and NSF through NSF’s MRI Program) is one of our main research tools. The new FEG STEM/HRTEM will benefit our research in studying microstructures, reaction fronts, and interface structures in minerals at the atomic scale.

Fig. 2c

Above: Nano-minerals in nature: (A) 2-D nanosheets (vernadite); (B) 1-D nano-rods (palygorskite); (C) Nanoparticles (ferrihydrite) (Elements, 2008, 4, p. 376)


Fig. 2

Above: A new environment sensitive phase diagram for the titania nano-crystals (Barnard and Xu, 2008, ACS NANO, 2, 2237-2242)

♦ Effects of size and morphology of nano-crystals and nano-precipitates on their reactivity and stability: When crystals decrease in size, contributions from their interface energies increase significantly. This affects the structure, reactivity, and stability fields on their phase diagrams. For both nano-crystals and nano-precipitates, we integrate experimental work with theoretical modeling using density function theory to build relationship between size, morphology, and interfaces with host phases. Nano-precipitates that record evolutionary histories of their host rocks are common in rock-forming minerals of metamorphic and igneous rocks. This project is supported by NSF.


Fig. 3Left: Nanoporous silica for studying the pore size effect on uranium redox reactions.

♦ Nanopore controlled geochemical processes: The behavior of geological fluids in nanopores is significantly different from those in normal non-nanoporous environments; the nanopore environment affects both dielectric property of solvent water and solvation of dissolved metal ions. We investigate the effect of nanopore surfaces on sorption / desorption, and redox reactions of radionuclide of uranium and other heavy metals. This project is supported by Office of Biological and Environmental Research, U. S. Department of Energy.


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