Quinton L. Williams

In vitro evaluation of cytotoxicity of engineered carbon nanotubes in selected human cell lines

In this study, we used a systematic approach to study and compare the in vitro cytotoxicity of selected engineered carbon nanotubes (CNTs) to test cell lines including human skin keratinocytes, lung cells and lymphocytes. Results of fluorescein diacetate (FDA) uptake in T4 lymphocyte A3 cells indicated cytotoxicity caused by single-walled carbon nanotubes (SWCNTs) at concentrations of 2, 5 and 10ppm. At 2ppm, the SWCNT treatment group retained 71.3% viability compared to the PBS control group. At 10ppm, cellular viability further decreased to 56.5% of the PBS control group. In the skin keratinocyte HaCaT cells and lung MSTO-211H cells, the SWCNT did not demonstrate any cytotoxicity at concentrations of 2 and 5ppm but slightly inhibited HaCaT cells and caused significant toxicity to MSTO-211H cells at 10ppm. Multi-walled carbon nanotube (MWCNT) testing showed significant cytotoxicity to A3 cells in a dose-dependent manner. At 10ppm the viability of the cells decreased to 89.1% compared to the PBS control. In MSTO-211H cells, MWCNT caused significant toxicity at concentrations of 2ppm and higher. By comparison, HaCaT cells were inhibited significantly only at 10ppm. Overall, the test CNTs inhibited cellular viabilities in a concentration, cell type, and CNT type-dependent pattern. The viabilities of the MWCNT-impacted cells are higher than the corresponding SWCNT groups. We speculate that on a per volume basis, the greater availability of defects and contaminants for cellular interaction may contribute to the higher cytotoxicity of SWCNT in this study. The interaction between the SWCNTs and A3 lymphocytes was also observed by scanning electron microscopy. The mechanism for causing cell death in this study was attributed to apoptosis and necrosis after physical penetration by CNTs and oxidative stress via formation of reactive oxygen species.

Boron-doped carbon nanotube coating for transparent, conducting, flexible photonic devices

Conducting transparent polymer materials were made by applying boron-doped single-walled carbon nanotubes to the surfaces of glass and flexible polyethylene terephthalate film substrates. Optical transmission and sheet resistance measurements showed that the boron-doped coated samples had sheet resistances of ∼7kΩ∕◻ and flat optical transmission of ∼89% for visible light. Temperature and humidity tests showed that the materials remained conductive after nearly 150h of testing. The materials are robust and even maintain their conducting properties after being folded. Fabrication of a simple light emitting device demonstrates usage of the material as a flexible transparent electrode.

Vanadium Oxide Nanorods for Li-Ion Battery Applications

Vanadium oxide (V 2 O 5 ) nanorods of size 10-50 nm diameter with a length of several micrometers were synthesized from xerogels through a template-free simple hydrothermal process. The pristine products were then characterized using X-ray diffractometry, Fourier transformation infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and cyclic voltammetry. The measured specific charge for template-free V 2 O 5 nanorods is 385 mAh/g during the initial discharge process. A decrease in the specific charge during cycling indicates the loss of electronegativity.

Headgroup dimerization in methanethiol monolayers on the Au(111) surface : A density functional theory study

A long-standing controversy related to the dimer pattern formed by S atoms in methanethiol (

Sensitivity modeling study for an ozone occurrence during the 1996 Paso Del Norte Ozone Campaign.

CH_{3}SH

Hydrogen Storage on Platinum-Decorated Carbon Nanotubes with Boron, Nitrogen Dopants or Sidewall Vacancies

) on the Au(111) surface has been resolved using density functional theory. For the first time, dimerization of methanethiol adsorbates on the Au(111) surface is established by computational modeling. For methylthiolate (

How does an external electrical field affect adsorption patterns of thiol and thiolate on the gold substrate

CH_{3}S

C H 3 S H molecules deposited on Cu(111) and deprotonation

), it is shown that the S atoms do not dimerize at high coverage but reveal a dimer pattern at intermediate coverage. Molecular dynamics simulation at high coverage demonstrates that the observed dialkyl disulfide species are formed during the desorption process, and thus are not attached to the surface.

Thirty Years of Meteorological Education at a Historically Black University

Surface ozone pollution has been a persistent environmental problem in the US and Europe as well as the developing countries. A key prerequisite to find effective alternatives to meeting an ozone air quality standard is to understand the importance of local anthropogenic emissions, the significance of biogenic emissions, and the contribution of long-range transport. In this study, an air quality modeling system that includes chemistry and transport, CMAQ, an emission processing model, SMOKE, and a mesoscale numerical meteorological model, WRF, has been applied to investigate an ozone event occurring during the period of the 1996 Paso del Norte Ozone Campaign. The results show that the modeling system exhibits the capability to simulate this high ozone occurrence by providing a comparable temporal variation of surface ozone concentration at one station and to capture the spatial evolution of the event. Several sensitivity tests were also conducted to identify the contributions to high surface ozone concentration from eight VOC subspecies, biogenic VOCs, anthropogenic VOCs and long-range transportation of ozone and its precursors. It is found that the reductions of ETH, ISOP, PAR, OLE and FORM help to mitigate the surface ozone concentration, and like anthropogenic VOCs, biogenic VOC plays a nonnegligible role in ozone formation. But for this case, long-range transport of ozone and its precursors appears to produce an insignificant contribution.

Thioglycolic acid on the gold (111) surface and Raman vibrational spectra.

The interaction between hydrogen molecules and platinum (Pt)-decorated carbon nanotubes (CNTs) with boron (B)-, nitrogen (N)-dopants or sidewall vacancies is discussed from first-principle calculations. The adsorption patterns of hydrogen molecules on four types of Pt-decorated CNTs are investigated, and the partial density of states projected on the Pt atom is computed to reveal the response to the number of hydrogen molecules, dopants or vacancies. It is found that the B-, N-dopants or sidewall vacancies can adjust the binding energy between the hydrogen molecules and the Pt atom deposited on the defective CNT, while not reducing the maximum number of hydrogen molecules that are chemically adsorbed on the Pt atom. It is demonstrated that the binding energy of the first H2 and the Pt atom on the pristine CNT or the CNT with the B-, N-dopants is quite strong, so each Pt atom in these three cases can only release the second H2 under ambient conditions. However, when the Pt atom is deposited on the CNT with sidewall vacancies, it can adsorb and desorb two hydrogen molecules under ambient conditions.