Erwin D. Poliakoff - US grants

Dr. Erwin D. Poliakoff is supported by a grant from the Experimental Physical Chemistry Program to study synchrotron radiation induced fluorescence from molecular ions. These measurements give valuable insight into how electronic and nuclear motions are correlated in excited molecules; moreover, these results will also tell us about the origins of various light sources in the galaxy. This work focuses on the correlation of electronic and nuclear motion (Franck-Condon breakdown), as well as related electron correlation effects (continuum coupling). Dispersed fluorescence has been used in previous work to demonstrate that resolution is not limited by the excitation band width. This capability will permit studies that would not otherwise be feasible, including work on the photoionization of van der Waals species, transfer of shape resonant character between ionization continua and fluorescence from doubly-charged diatomic ions.

9315857 Poliakoff In this project in the Experimental Physical Chemistry Program of the Chemistry Division, Erwin Poliakoff of Louisiana State University will pursue highly resolved studies of resonant photoionization using synchrotron radiation as the excitation source. The deposition and partitioning of energy in the product ions will be determined from dispersed fluorescence. Highly resolved data are thus accessible over a broad electron energy range to help elucidate the photoejection dynamics. These data will be applied to systems which are vibrationally resolved for polyatomic targets and rotationally resolved for diatomic molecules. %%% In the experiments performed in this project, the motions that electrons make when molecules dissociate under the influence of high energy light will be correlated with the motions of the nuclei. The light used in these studies will come in part from a synchrotron radiation source at Louisiana State University. The data acquired in these studies is inaccessible by other techniques and will be used to guide and shape theoretical models for these processes. ***

This project aims to show how an X-ray spectroscopy apparatus can be used to probe detailed microscopic aspects of pollutant formation that occur at interfaces in combustion sources. Many pollutants are introduced into the environment as a result of combustion processes, and there is a growing realization that important pathways related to the production of the pollutants involve heterogeneous processes, i.e., surface reactions, for which, there is no clear mechanistic picture of the reaction pathways or kinetics. This project carries to develop instrumentation that generates essential information regarding how pollutants with significant health effects are formed, and thereby provide the knowledge required for reducing their production. An end-station for synchrotron-based x-ray spectroscopy experiments will be developed for monitoring microscopic aspects of combustion processes. The end-station will be a vacuum system with a temperature-regulated sample holder that can be dosed with reactants of interest. The system will be designed so that fluorescence yield XAFS(s-ray absorption fine structure) spectroscopy can be performed in a variety of ways. Different types of x-ray spectra will be generated. Extended x-ray absorption fine structure (EXAFS) spectroscopy will be used for determining structural information, and x-ray absorption near edge structure (XANES) spectroscopy will be used for chemical fingerprinting applications. Specifically, this end-station will be optimized for probing how chlorine-containing aromatic species (e.g., chlorophenols) are adsorbed on metal oxide surfaces, and how they react to form polychlorinated dibenzo-p-dioxins and dibensofurans (PCDD/Fs). EXAFS spectra will be used to determine how aromatic compounds (such as 2-chlorophenol) are adsorbed on oxidized metal surfaces. Also, EXAFS spectra will be used to determine structural information on reaction intermediates after the reaction has been allowed to progress. It will also be possible to generate kinetic data on combustion processes by probing a more limited spectral range, the XANES region.
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The key point unifying these ideas is that by combining techniques from environmental science and x-ray spectroscopy, wholly new types of data can generated to elucidate chemical pathways that generate pollutants in combustion processes. Students trained in areas of instrumentation development and applications to environmental sciences, which are also priorities for U.S. industry, will be highly competitive in this job market.

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.

Environmentally persistent free radicals (EPFRs) are formed on surfaces of transition metal oxides when molecules chemisorb on them. Electron transfer from the molecule to the metal results in reduction of the metal and the creation of spin density on the organic molecular adsorbate, i.e., formation of the EPFR. These interfacial pollutants are relatively stable (i.e., persisting for hours or days), so they can enter the environment and have deleterious health effects. Moreover, these systems are particularly prevalent at Superfund sites, so it is essential that they be studied and characterized in order to understand their roles in human health impacts in the vicinity of Superfund sites. However, these systems are complex and difficult to characterize, so we have designed this project to understand the detailed structural and chemical transformations that are responsible for their creation. Specifically, this project explores the physical and chemical characteristics of these particle-bound pollutants primarily using x-ray spectroscopy and TEM analysis. There are three Specific Aims: (1) Develop methods for controlled, reproducible generation of metal oxide-containing nanoparticles as surrogates of nanoclusters found in real-world environments, (2) Characterize the metal nanoparticles, structurally and electronically, and (3) Determine the surface processes and interactions of CHCs that lead to the formation of persistent free radicals and other toxic pollutants. This project characterizes the electron properties of the particle surface, which is indispensable for the other projects. Collaboration with Project 1 will lead to understanding of the structure and electronic properties of the EPFRs, which will allow those researchers to understand the factors affecting EPFR formation and reactivity. It generates background for studies of EPFRs in Superfund soils in Project 3. It similarly provides the chemistry necessary to understand the health effects induced by inhalation of EPFRs demonstrated in biomedical projects 2, 4, and 5. Finally, the structural characterization of the metal oxide particles and the surface-bound molecules will be indispensable for both the Computational Core, as well as the Materials Core.