Randall W. Hall - US grants

In this project in the Theoretical and Computational Chemistry Program of the Chemistry Division, Professor Hall will develop new mathematical models for the study of clusters of metals such as sodium. This will eventually lead to more complex investigations of disordered condensed phases. The path integral formulation of quantum mechanics will be used to study sodium metal clusters, the elctron gas, and as a means for determining the Mott transition in sodium. The long term goal of this research is to develop methods that are capable of determining correlated electron properties in disordered condensed phase systems. The studies of sodium metal clusters will focus on determining the extent of electron delocalization as a function of cluster size. The electron gas and bulk sodium calculations will investigate aspects of the insulator-metal transition.

High performance computing (HPC) is a major initiative at Louisiana State University (LSU). Its multidisciplinary research programs focus on grand challenges in materials science, astronomy, microsystems design, and environmental studies. To advance this effort, we request five NSF Traineeships. Consortial arrangements have been made to recruit in-state and out-of-state students, especially minorities from Historically Black Institutions. Innovative training structures have been introduced to integrate HPC into graduate education and research. These include new cross-disciplinary curricula and a dual-degree program to allow Ph.D. students in the physical sciences to get a M.S. from Computer Science and vice versa. Unique opportunities are available for graduate trainees to interact with scientists at Oak Ridge and Argonne National Laboratories, Mobil and Ethyl Corporations, and in Europe and Japan. To establish the HPC effort a LSU, two excellent parallel computing laboratories have been set up with $2. million in infrastructure grants from the State of Louisiana. These laboratories feature an 8,192-node MasPar, a 64-cell iWarp, and 8-node iPSC/860, and an 8-processor Silicon Graphics. With the latest grant of $850,000, we plan to acquire a 56-node Intel Paragon.

This project, carried out by Professors Leslie Butler and Randall Hall of Louisiana State University and their students, and Dr. Larry Simeral of the Albemarle Corporation, and supported by Analytical and Surface Chemistry, uses nuclear magnetic resonance spectrometry based on the nuclei 2H, 17O, and 27Al to characterize the active catalytic site of methylaluminoxane, a co-catalyst used in new generation Ziegler-Natta catalysis for olefin polymerization. The 27Al sites exhibit large quadrupolar interactions that require special methods developed in the PI's laboratory for successful measurement of the NMR spectra. Density functional and molecular orbital calculations are used to model the observed quadrupolar interactions, and then the observed NMR spectra are correlated with the calculated structures. This GOALI project contains an academic and industrial collaboration between the PIs at Louisiana State University and scientists at Albemarle Corporation.

Ziegler Natta catalysts are used in industrially important reactions that produce polymers and plastics. A catalyst involves a specific site on a molecule where the reaction occurs. Despite the wide use of the Ziegler Natta catalyst based on a compound called methylaluminoxane, the nature of the catalytic site is unknown. Small differences in catalyst preparation lead to large differences in catalytic efficiency, and there is therefore much interest in determining the nature of that site. Professors Leslie Butler and Randall Hall of Louisiana State University and their students will use unique spectroscopic techniques to establish the nature of that site, in collaborative work with scientists at Albemarle Corporation, a producer and user of the catalytic material.

PROJECT SUMMARY

The goal of this work is to determine from what fuels and under what conditions persistent radicals are formed in combustion systems and ultimately incorporated into airborne fine particulate matter (PM2.5). Specific objectives include:

1. To determine experimentally how known semiquinone radical precursors react under post-flame combustion conditions and under which conditions they form radicals. This is done using a high-temperature flow reactor/gas chromatograph/mass spectrometer system to study the thermal reactions of hydroquinone and catechol under oxidative and pyrolytic conditions. Effluent is trapped using cryogenic techniques for analyses by electron paramagnetic resonance (EPR).

2. To determine experimentally the combustion conditions under which various common fuels generate stable free radicals. Laboratory reactors are used to study the thermal degradation of various fuels and to trap free radicals for characterization. Candidate fuels include: propane, gasoline, diesel fuel, biodiesel fuel, No. 6 fuel oil, coal, wood, and a chlorinated hydrocarbon mixture.

3. To identify which precursors and particle surfaces form and stabilize persistent free radicals. The chemisorbed radical hypothesis is investigated by dosing surrogate particle samples with semiquinone-type radical precursors using a packed-bed reactor system. The particles investigated include activated carbon and silica or alumina doped with iron, copper, magnesium, calcium or zinc. Radical precursors studied include hydroquinone, catechol, phenols, benzenes, and chlorinated analogues..

4. To determine if carbonaceous materials form persistent free radicals. The intrinsic radical hypothesis is investigated by generating and modifying soots or chars formed by thermal degradation of fuels. The particles will be characterized for radicals before and after partial oxidation with various oxidants (O2, NO2, OH, O, and Cl). The radical concentrations and lifetimes are determined by EPR.

5. To elucidate the structure, stability, and reactivity of semiquinone-type radicals using ab-initio calculation techniques. Density function theory (DFT) procedures are used to calculate the structures, energies, and spin densities of radicals derived from hydroquinone and catechol as well as related radicals identified in the experimental tasks.

6. To demonstrate whether similar persistent radicals are associated with full-scale combustion-derived and ambient PM2.5 samples. A limited number of full-scale combustion and airborne PM2.5 samples are characterized to quantify associated radicals and the metals (iron, copper, magnesium, calcium, zinc) that may have a role in stabilizing them.

Broader Impacts

The concept of persistent, combustion-generated free radicals is an area that needs exploratory research to establish the nature, origin, and reactivity of these radicals under a variety of conditions. This project is designed to provide this information so that the research community can further explore the impact of persistent radicals under specific conditions and for specific applications. It also supports an ongoing collaboration with Drs. William A. Pryor and Guiseppe Squadrito of the Biodynamics Institute at LSU and other health-effects researchers at LSU and
Tulane Medical School. The results of this study form a basis for detailed studies of the biological chemistry and health impacts of persistent free radicals.

NIRT: Combustion-Generated Nanoparticles--
The Role of Transition Metals in Nanoparticle and Pollutant Formation

CTS-0404314

This project addresses: 1.) The role of combustion-generated metal oxide nanoparticles in the formation/growth of primarily carbonaceous nanoparticles and 2.) The role of metal oxides condensed on growing nanoparticles in the formation of organic pollutants. Ni and Cu have been identified as important metals for initial study. The reactivity of their oxides under a range of conditions is being studied using a variety of experimental techniques. Dendrimeric synthesis techniques is used to create 1-3 nm metal oxide nanoparticles with and without associated carbonaceous layers; sol-gel techniques are used to create thin metal-oxide films on carbon and silica. The reactions of organic chemicals with these nanoparticle surrogates from 200 to 1100 C under oxidative and pyrolytic conditions are studied using a high-temperature flow reactor coupled with GC-MS, EPR, and FTIR analysis. Metal-catalyzed PAH formation is studied using HPLC-UV absorption. The nature of the metal oxides and their chemical binding is characterized using x-ray spectroscopic techniques at the LSU synchrotron facility. Ab initio modeling techniques are used to assess nanoparticle geometries, reaction sites, possible reaction mechanisms, and how they may vary as a function of particle size and metal identity.
It has been estimated that over 650,000 people die prematurely in the US each year due to exposure to airborne fine particles. PM2.5, defined as particles with a mean aerodynamic diameter of less than 2.5 microns, have been shown to initiate cardiopulmonary disease and cancer in exposed populations. It has been realized only recently, however, that submicron, combustion-generated nanoparticles are the likely cause (alone or in combination with other pollutants) for the majority of these deaths and associated illnesses. Although health-effects research programs have been initiated by NIH and EPA, the causative agents remain unknown and progress is hindered by lack of understanding of the complex composition and reactivity of combustion-generated nanoparticles. The impetus of this program is practical, viz. to understand the origin and nature of combustion-generated nanoparticles so that their environmental impact can be minimized. The goal is contribute to the understanding of the chemical factors impacting the health effects of combustion-generated nanoparticles so that their effects can be mitigated or eliminated through combustion control.

Professors Leslie G. Butler and Randall W. Hall of the Louisiana State University and Agricultural and Mechanical College are supported by the Analytical and Surface Chemistry Program in the Division of Chemistry for conducting three- dimensional chemical analysis and molecular simulations with applications to flame retardants in polymers. The application of three-dimensional imaging methods to chemistry is new, thus, methods for image analysis will be developed. Images will be acquired with synchrotron X-ray tomography in a mode that yields elemental concentrations throughout a 2 millimeters cube at a resolution of 3 micrometers. As sample ages, it is expected that good flame retardants dissolve into the polymer and bad flame retardants form internal domains and surface blooms. The diffusion rates, activation energies, and diffusion mechanisms will be measured experimentally and compared with theoretical simulations.
Three-dimensional imaging offers new views of chemistry in solids, like the diffusion of molecules through glassy polymers. Computer simulations of glasses can describe the structure and dynamics of glasses and thus diffusion of molecules through a glass. A practical example is the slow (years) diffusion of flame retardants through polymers. Sometimes, the dusty feel on old CRTs and printer cases is caused by the precipitation of flame retardants and is informally called "blooming". A common example of blooming is the diffusion and surface precipitation of cocoa butter on the surface of old chocolate. A web-based tutorial will be created to introduce the students to basic sciences and the three dimensional image analysis aspects of this research.

CTS-0625548 Award Abstract

Title: The Role of Transition Metals in Formation of Environmentally Persistent Free Radicals

This research will study the role of common transition metals in the formation and stabilization of environmentally persistent free radicals (PFRs) that have been linked to adverse health impacts. Previous research by the PI has clearly demonstrated that combustion systems can generate PFRs when substituted organic molecules react on the surface of Cu(II)O-containing particles such as are found as combustion-generated particulate matter. Co-ordination of the radical with the metal stabilizes it against atmospheric oxidation. Electron paramagnetic resonance (EPR) studies indicate that these radicals exist unchanged under atmospheric conditions for up to 24 hours and persistent indefinitely in a somewhat altered form. Collaborative studies with biomedical researchers have demonstrated that these radical-particle systems induce oxidative stress in exposed tissues that lead to DNA damage as well as pulmonary and cardiovascular dysfunction. Similar results were observed for airborne fine particulate matter (PM2.5) and samples of combustion-generated particulate matter, suggesting that these radicals may be responsible for at least some of the reported health impacts of PM2.5.

Copper, iron, and vanadium appear to be the most favorable metals for inducing formation of PFRs. Radical formation and stabilization from various molecular precursors will be studied using EPR, X-ray, and FTIR spectroscopic techniques and laboratory-prepared surrogate particles in the manner successfully used in the previous study of Cu(II)O. Ab initio methods will be used to calculate reaction energies, charge distributions, and EPR spectra of model radical-particle systems. Matrix isolation EPR will be used to generate standards of spectra of relevant radicals to assist in identification of PFRs in a more complex environment. Solvent extraction and GC-MS analysis will be used to determine whether PFRs are extractable or if they are converted to molecular species during the extraction process.

Broader Impacts: It is not generally known within the combustion community that combustion generated particles contain PFRs. In addition to the health impacts of persistent radicals, radicals may be key intermediates in the formation of many pollutants including polychlorinated dibenzo-p-dioxins and polychlorinated furans (PCDD/F). This project is designed to provide key information so that the research community can further explore the impacts of persistent radicals under specific conditions and for specific applications. In addition to graduate student involvement, an undergraduate researcher has been identified to conduct the extraction and chemical analysis task as a REU project that will result in the preparation of an undergraduate research thesis.

Professors Les Butler and Randall Hall of Louisiana State University and co-PI Larry Simeral of Albemarle Corp. are supported by the Analytical and Surface Chemistry Program in the Division of Chemistry (with co-funding from the GOALI program in the Engineering Directorate) to develop tomographic and simulation-based approaches to real-time characterization of the motion of small molecules through glasses. Specific applications address flame retardants and hydrogen storage materials. The work entails a partnership with Albermarle Corporation in a GOALI context.

Derived advances could have revolutionary impact on sustainable industrial chemistry. In addition to these impacts in important areas of energy and materials safety, the work derives broad impact from development of training modules for enhanced utilization of visualization tools in research and learning.

The Computational Core will support the work of the center by calculating the properties and reactivities of models for metal oxide ultrafine particles (UFPs) and fine particles (FPs) suggested by experiment. The models of UFPs will include up to 20 metal atoms and a varying number of oxygen atoms. Reactions of these models with chlorinated benzenes and phenols to form environmentally persistent free radicals (EPFRs) and dioxins will be studied. The goal will be to provide a more complete understanding of the experimental results by identifying particularly important cluster geometries and sites on these clusters for comparison with the results for larger particles. The Core will utilize the computational facilities available at Louisiana State University and within the State of Louisiana. Louisiana State University's High Performance Computing group maintains approximately 21.5 TFIops of computing power spread over approximately 2000 cores. The Louisiana Optical Network Initiative's computing facilities provide approximately 45 TFIops of computing power spread over approximately 6000 cores. Standard software is available on these computers including Gaussian, GAMESS, NWChem, Wein, Charmm, CPMD, Gromacs, NAMD, PINY-MD, and VMD. The bulk of the computational support will use the ab initio programs Gaussian09 and CPMD, which can perform first principles calculations. Density functional calculations will use the aug-cc-pVDZ and LANL2DZ basis and selected functionals. Gaussian09 includes the MOB functional of Truhlar, which is optimized for use with transition metals. This functional, along with B3LYP and other selected hybrid functionals, will be used to optimize the geometric structures of metal oxide clusters and metal oxide-EPFR complexes. The calculated atomization and ionization energies, the electron affinities, and the charge and spin densities will be used to characterize the clusters of copper and iron oxides. The EPFR-cluster complexes formed by reaction with 2-monochlorophenol and 1,2-dichlorobenzene will be determined. The AEs of reaction, selected activation energies, and vibrational frequencies will be compared with experiment. Metal oxide clusters will be optimized for different spin states in order to determine the lowest energy spin state.