Chemical and biological behavior of single-walled carbon nanotubes in the aquatic environment

Professor Lee Ferguson

Department of Chemistry and Biochemistry, University of South Carolina

12:30 pm on April 30 in Teer 203

Lunch will be served at 12:00 in the Teer lobby.

Abstract: Single-walled carbon nanotubes (SWNTs) are filamentous manifestations of a repeating aromatic carbon structure formed into an open cylinder. Because of their unique physicochemical properties and potential for large-scale commercialization, concerns have emerged over potential adverse effects of nanomaterials such as SWNTs in the aquatic environment. These concerns include direct toxicity to aquatic organisms as well as potential effects on distribution of hydrophobic organic contaminants (HOC) through adsorptive sequestration.  This presentation will focus on a summary of work performed to date in my laboratory aimed at elucidating the environmental effects and fate of these novel contaminants in aquatic systems.  In simulations of natural aquatic systems, it has been observed that SWNTs can be stabilized in colloidal solutions by coating with natural organic matter, but that this stability is highly dependent on solution ionic strength.  Increasing ionic strength leads to aggregation of SWNTs as well as deposition of these materials to suspended particulates.  In addition, SWNTs adsorb HOCs strongly from aqueous solutions.  Taken together, these results indicate that these carbon nanomaterials will associate strongly with sediments in aquatic systems, where they may become important in modulating fate of co-occurring molecular contaminants.  Toxicity assays indicate that while purified SWNTs themselves are relatively non-toxic to benthic deposit feeders, their carbonaceous manufacturing byproducts may cause deleterious effects to these organisms.  Radiotracer (14C-SWNT) uptake experiments in benthic organisms indicate that SWNTs are not bioaccumulated from ingested sediments; however, organisms ingesting SWNT-associated HOCs (e.g. PAHs, PCBs, and PBDEs) accumulate these contaminants in their tissues.  The implications of these findings will be interpreted in context of potential ecotoxicological hazards posed by contamination of aquatic systems with SWNTs.

Second-generation TiO-based nanocomposites for solar fuel generation

Professor Kimberly Gray
Department of Civil and Environmental Engineering, Northwestern University

12:00 pm on April 21 in Teer 203

Lunch will be served at 11:30 in the Teer lobby.

Abstract: Since Fujishima and Honda developed the photoelectrochemical cell for H2O splitting in 1972, heterogeneous photocatalysis has attracted much attention. TiO2 is among the most extensively studied semiconductor photocatalysts. It is chemically and biologically inert, photocatalytically stable, commercially available, and inexpensive. Excited charge carriers created by illumination with sufficiently energetic light promote highly reactive radicals with robust reducing and oxidizing capacity that may recombine, become trapped in metastable surface states, or react with electron acceptors and electron donors adsorbed on the TiO2 surface.

In the past three 30 years, most of the work in the photocatalytic field has focused on energy and environmental applications, which require materials with the following properties: (1) hindered charge recombination and improved photocatalytic efficiency; (2) targeted reactivity and selectivity that match band energies to the desired reaction, and (3) extended photoresponse into the visible light region. Masakazu Anpo first introduced the notion of “second-generation” TiO2 photocatalysts, which can absorb visible light and also operate effectively as photocatalysts. We hypothesize that the solid-solid interface in TiO2-based nanocomposites is key to overcoming these three challenges. Recent findings in our laboratory and others throughout the world reveal a number of surprising insights as to why TiO2 nanocomposites tend to display higher photoactivity than pure-phases and point to the critical role of the solid-solid interface as the location of defect sites that serve as catalytic “hot spots”.

We prepare highly active TiO2 nanocomposites using chemical and physical methods in our laboratory. By varying key fabrication conditions (target power, substrate bias, oxygen partial pressure, and deposition angle) in reactive DC magnetron sputtering, we synthesize TiO2 thin films with different microstructures and interfacial densities in sufficient quantities to allow structural characterization and functional interrogation. This paper will report the synthesis and characterization of photocatalytic films and their use to generate solar fuels and oxidize gas phase contaminants.

Recent Developments in Tall Building Design

Shane McCormick, Martin/Martin, Inc. Consulting Engineers

12:30 pm on 3/19 in Room 203 Teer.

Lunch will be served in the lobby at Teer.

Abstract: Despite the events of September 11 and the collapse of the World Trade Center Towers, there has recently been a resurgence of tall building construction. We will discuss this trend and two towers currently under construction. Trump Tower is a luxury condominium building in Chicago that will be the tallest building constructed in the United States in 30 years. Burj Dubai is a mixed-use tower in the United Arab Emirates that will be the tallest freestanding structure in the world. We will also discuss wind tunnel testing, ultra high-strength concrete, long-term concrete behavior, structural systems, and aerodynamics.

Ultrafine Atmospheric Aerosol, Clouds and Climate

Jeffrey Pierce, Carnegie Mellon University

Wednesday, February 27, 2008 Seminar 12:30-1:30 Teer 203

Lunch to be served in the Teer Lobby at noon.

Abstract: Atmospheric aerosol regulates climate by scattering and absorbing radiation and by altering the radiative properties of clouds. Estimates of how humans are affecting the energy balance of the planet are uncertain largely due to complicated interactions between aerosols and clouds. A major factor in this uncertainty is the how humans have changed the number of particles in the atmosphere that may act as cloud condensation nuclei (CCN). Ultrafine particles (particles with diameters smaller than 100 nm), are often too small to act as CCN; however, a large fraction of particles in the atmosphere begin as ultrafine particles and must grow to CCN sizes. In this talk we will explore how uncertainties in ultrafine aerosol sources, such as nucleation and emissions from primary sources, lead to uncertainties in predictions of CCN concentrations and cloud albedo. The impact of these ultrafine particles on CCN will be explored using both a simple model of aerosol timescales as well as a detailed 3-D general circulation model with detailed aerosol microphysics. The importance of reducing uncertainties in primary particle emission rates as well as new particle formation rates in predictions of cloud albedo are assessed. Finally we explore the potential link between cosmic ray intensity and cloud properties through changes in ion-induced new particle formation rates.