Jessica D. Torrey

Kinetics of zero valent iron nanoparticle oxidation in oxygenated water.

Zero valent iron (ZVI) nanoparticles are versatile in their ability to remove a wide variety of water contaminants, and ZVI-based bimetallic nanoparticles show increased reactivity above that of ZVI alone. ZVI nanoparticles degrade contaminants through the reactive species (e.g., OH*, H(2(g)), H(2)O(2)) that are produced during iron oxidation. Measurement and modeling of aqueous ZVI nanoparticle oxidation kinetics are therefore necessary to optimize nanoparticle design. Stabilized ZVI and iron-nickel nanoparticles of approximately 150 nm in diameter were synthesized through solution chemistry, and nanoparticle oxidation kinetics were determined via measured mass change using a quartz crystal microbalance (QCM). Under flowing aerated water, ZVI nanoparticles had an initial exponential growth behavior indicating surface-dominated oxidation controlled by migration of species (H(2)O and O(2)) to the surface. A region of logarithmic growth followed the exponential growth which, based on the Mott-Cabrera model of thin oxide film growth, suggests a reaction dominated by movement of species (e.g., iron cations and oxygen anions) through the oxide layer. The presence of ethanol or a nickel shell on the ZVI nanoparticles delayed the onset of iron oxidation and reduced the extent of oxidation. In oxygenated water, ZVI nanoparticles oxidized primarily to the iron oxide-hydroxide lepidocrocite.

Scanning Probe Direct‐Write of Germanium Nanostructures

Bottom-up nanostructure synthesis has played a pivotal role in the advancement of nanoscale science. This approach is typically less labor and energy intensive than its topdown counterpart because only the required amount of material is grown from a chosen precursor, rather than a macroscopic object being chiseled down to the desired size. However, device integration often requires complex manipulation steps for placing the synthesized nano-object in the appropriate location.

Processing and Characterization of Nanoparticle Coatings for Quartz Crystal Microbalance Measurements.

The quartz-crystal microbalance is a sensitive and versatile tool for measuring adsorption of a variety of compounds (e.g. small molecules, polymers, biomolecules, nanoparticles and cells) to surfaces. While the technique has traditionally been used for measuring adsorption to flat surfaces and thin ridged films, it can also be extended to study adsorption to nanoparticle surfaces when the nanoparticles are fixed to the crystal surface. The sensitivity and accuracy of the measurement depend on the users’ ability to reproducibly prepare a thin uniform nanoparticle coating. This study evaluated four coating techniques, including spin coating, spray coating, drop casting, and electrophoretic deposition, for two unique particle chemistries [nanoscale zero valent iron (nZVI) and titanium dioxide (TiO2)] to produce uniform and reproducible nanoparticle coatings for real-time quartz-crystal microbalance measurements. Uniform TiO2 coatings were produced from a 50 mg/mL methanol suspension via spin coating. Nanoscale zero-valent iron was best applied by spray coating a low concentration 1.0 mg/mL suspended in methanol. The application of multiple coatings, rather than an increase in the suspension concentration, was the best method to increase the mass of nanoparticles on the crystal surface while maintaining coating uniformity. An upper mass threshold was determined to be approximately 96 µg/cm2; above this mass, coatings no longer maintained their uniform rigid characteristic, and a low signal to noise ratio resulted in loss of measurable signal from crystal resonances above the fundamental.

Serial and parallel Si, Ge, and SiGe direct-write with scanning probes and conducting stamps.

Precise materials integration in nanostructures is fundamental for future electronic and photonic devices. We demonstrate Si, Ge, and SiGe nanostructure direct-write with deterministic size, geometry, and placement control. The biased probe of an atomic force microscope (AFM) reacts diphenylsilane or diphenylgermane to direct-write carbon-free Si, Ge, and SiGe nano and heterostructures. Parallel direct-write is available on large areas by substituting the AFM probe with conducting microstructured stamps. This facile strategy can be easily expanded to a broad variety of semiconductor materials through precursor selection.

Oxidation behavior of zero-valent iron nanoparticles in mixed matrix water purification membranes

Morphological changes resulting from the oxidation of zero valent iron (ZVI) nanoparticles were measured as an assessment of their mechanical robustness in mixed matrix membranes for water treatment applications. Upon oxidation from metallic iron to iron oxide hydroxide, FeO(OH), particles underwent a significant transformation in size and morphology from 100 nm diameter spherical particles to plate-like crystalline particles with a hydrodynamic diameter greater than 450 nm. Atomic force microscopy (AFM) was used to mechanically degrade the FeO(OH) crystallites during repeated imaging. To determine whether similar degradation would occur during water filtration in a mixed matrix membrane, force under standard membrane operating conditions was calculated. Such force calculations were used to compare the shear forces exerted during water flux in a mixed matrix membrane to the normal forces imparted by AFM. Analysis suggested that the oxidized ZVI nanoparticles will experience a 10−19 N maximum shear force in pore channels, much lower than the imaging forces in AFM, suggesting the mechanical stability of the particles during water remediation. Additional quartz crystal microbalance experiments were performed to confirm the mechanical stability of the oxidized iron nanoparticles in the flow environments of ultrafiltration. Taken together, the results of this study demonstrate that the mechanical properties of the nanoparticle composite membranes are such that minimal mechanical degradation of the nanoparticles will occur during water filtration.

Ceramics for Sustainable Energy Technologies with a Focus on Polymer-Derived Ceramics

Due to their high hardness, high temperature stability, and high chemical stability, ceramic materials have significant uses and potential in existing and emerging sustainable technologies . In this paper, we provide a thorough overview of ceramics in a variety of sustainable applications. This is followed by a detailed discussion of an emerging process to make ceramics called polymer (or precursor)-derived ceramics . It is shown that due to the versatility of this process in making a wide range of shapes—fibers, coatings , and porous ceramics, this is an attractive route to make ceramics that will be a critical element in the next generation of sustainable technologies.