Environmental Toxicology: Nanoparticles and pollutant formation in combustion processes
B. Dellinger, R. McCarley, E. Poliakoff LSU Chemistry
Combustion processes produce pollutants and particulates (such as soot), and recent studies have shown that metal oxide particles are involved in their production. However, it is not understood how the pollutants are formed. Using x-rays at CAMD, Professors Barry Dellinger, Erwin Poliakoff, and Robin McCarley from the LSU Chemistry Department are studying the chemical reactions that occur on metal oxide surfaces. The goal of this research is to determine what is happening at the microscopic level in order to reduce pollutant formation in real-world processes. More specifically, the x-rays at CAMD are used in order to understand the structure and chemical properties of chemicals that attach to the surfaces of metal oxide surfaces, and the x-rays are indispensable for providing this information.
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| Metal oxide nanoparticles catalyze dioxin and PAH formation, and promotes formation of soot. Flame spans wide range of reaction temperatures.
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From: D’Alessio & co-workers Chemosphere 51 (2003) 1091 As particle size decreases, the fraction of metal increases and this metal catalyzes the formation of toxic materials |
Reduction and re-oxidation of CuO particles
 Before Reduction
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 After Reduction
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 After re-oxidation
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Why? (why metal oxides, why nanoparticles, why use x-ray spectroscopy?)
- Metal oxides promote dioxin production in combustion.
- Reactive organic radicals are stabilized by adsorption on metal oxides.
- X-ray spectroscopy provides detailed data on complex reaction mixtures
CuO nanoparticles (on SiO2 grains) prepared via dendrimer precursors
Preparation: Dissolve dendrimer in methanol. Add stoichiometric amount of Cu2+. Rotovap with SiO2. Heat at 450°C for ~4 hours.
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 Dendrimer precursors can be used to controllably synthesize a targeted range of nanoparticle sizes, allowing investigation of the correlation of size, activity, and elemental valence state
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XANES Spectra Cu(II) is predominant
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X-ray spectroscopy can help elucidate combustion mechanisms involving metals
There is considerable evidence implicating metallic nanoparticles with soot growth and toxic compound production
Dendrimeric precursors are useful for generating surrogate metal oxide nanoparticles
- good control of size and dispersity of nanoparticles
- very general, can be used with many different metals
- gas phase and tethered nanoparticles can be produced
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