Surface properties of soot nanoparticles

Amanda Nienow, advisors: Jeff Roberts (Chem), Mike Zachariah (ME)

In the atmosphere, particles in the nanometer size regime account for the greatest number count and carry the most surface area. These particles exhibit unusual characteristics including high surface-to-volume ratios and size dependent properties. The unusual characteristics of nanoparticles make them of scientific interest.

In our lab, work focuses on the surface properties of soot nanoparticles generated in a diffusion flame and size selected in a differential mobility analyzer (DMA). The goals of the project are to study and more completely understand the kinetics of soot oxidation, to develop a method for photoelectron spectroscopy at the surface of an aerosol, and to apply the new method to study the surface properties of soot particles. Achievement of these goals will provide fundamental information that could be used to develop technology to either remove or alter the soot particles emitted into the atmosphere.

Recent work on the oxidation kinetics of soot particles 40, 90, and 130 nm in diameter has been completed using a TDMA system. The results of the study characterize the oxidation rates of soot agglomerates. The three particle sizes studied were found to oxidize at different rates. It is of interest to see if smaller soot particles will exhibit a similar trend in oxidation rates. Therefore, the investigation of oxidation kinetics is currently being extended to primary soot particles of 10-30 nm in diameter.

Photoelectron spectroscopy is used to analyze the surface of materials in vacuum; without vacuum, the ejected electrons interact with the surrounding gas molecules and diffuse back to the positively charged material. Since nanoparticles are small compared to the mean free path of the electrons, the probability of the electron diffusing back to the particle is extremely small. This unusual property allows study of nanoparticles in a carrier gas through photoelectron spectroscopy. An aerosol photoelectron spectroscopy system is under design and will be used to study the surface of soot nanoparticles.