James Dewald

Formation of tellurium nanocrystals during anaerobic growth of bacteria that use Te oxyanions as respiratory electron acceptors

ABSTRACT Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here, we demonstrate that two anaerobes previously shown to be capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable stable-Te-isotopic fractionation (isotopic enrichment factor [ε] = −0.4 to −1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods (∼10-nm diameter by 200-nm length), which cluster together, forming larger (∼1,000-nm) rosettes composed of numerous individual shards (∼100-nm width by 1,000-nm length). In contrast, Sulfurospirillum barnesii forms extremely small, irregularly shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy-dispersive X-ray spectroscopy and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The use of microorganisms to generate Te nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods.

Microconcentrator photovoltaic cell (the m-C cell): Modeling the optimum method of capturing light in an organic fiber based photovoltaic cell

We propose a new architecture as an alternative method when constructing organic photovoltaics (PVs) by addressing the best method to trap resonant light within the devices using fiber optics to concentrate light in the form of a microconcentrator cell (m-C cell). Our initial effort is to address how the m-C cells manage light absorption using a mathematical model that considers all the required parameters including the incident angle, meridional plane, cross sectional area, and path length. By knowing the materials,refractive index, we are able to calculate the optical angular input to achieve maximum absorption of resonant light. We also addressed the complexity of how changing refractive indices in a multilayer device can alter the angular dependence when considering the incident input light. The consequence is that we can ensure efficient absorption of resonant light in a thin film yet without issues of transmission losses which are evident in all other thin film organic PVs.

Electron spin resonance and raman scattering spectroscopy of multi-walled carbon nanotubes: a function of acid treatment.

The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream.

Defect Analysis of Carbon Nanotubes

Raman spectroscopic analysis of plasma treated MWNTs was used characterize defects in MWNTs. Raman spectroscopy was also used to characterize defects induced via acid treatment. The Raman‐active disorder modes are used to fingerprint PSF attachment to MWNTs via defect states.

NMR Spectroscopy of Hydrogen Adsorption on Carbon Nanotubes

Hydrogen storage properties of both single‐ and multi‐walled carbon nanotubes (CNTs) under pressures up to 15 MPa are studied by nuclear magnetic resonance (NMR) spectroscopy. The role of residual metallic catalyst in hydrogen adsorption is studied by comparing purified samples with parent materials. Structural features such as diameter and defect density are determined by resonance Raman spectroscopy.

Tethering Carbon Nanotubes

Using Phosphorous Pentasulphide a new single step electrophilic route has been achieved to link Multi‐Walled Carbon Nanotubes covalently through a dithioester linkage. Raman spectra of the tethered tubes was collected using the In Via Renishaw Raman Spectrometer. FESEM images and AFM height analysis were also obtained for the linked tubes.