Characterization of Carbon Nanotubes and Graphitized Carbons as Adsorbents in a Microfabricated Vapor Preconcentrator/Focuser

Rebecca Veeneman is the first of two speakers for this seminar.
Within the WIMS Center Environmental Monitoring Testbed, we are developing a microfabricated preconcentrator/focuser for the micro-GC. The ?PCF permits detection of low analyte concentrations (ppb or ppt) and, if properly designed and operated, provides narrow injection plugs that enhance chromatographic resolution. Previously published work with ?PCFs has used arbitrary amounts of commercially available adsorbents. Models developed for larger adsorbent beds (grams) to trap vapors (ppm concentration) have not been applied to the micro-regime. We are extending the application of such models to new materials with decreasing bed masses (mg) and low-vapor concentrations by examining fundamental adsorption behavior. Adsorption isotherms have been determined for a range of vapors on graphitized carbons Carbopack B (C-B), Carbopack X (C-X), and carbon nanotubes (CNTs). For the common indoor air quality contaminant, benzene (~100 ppb), adsorption on CNTs was 1170?g/g compared to 368?g/g and 121?g/g for C-X and C-B, respectively. Toluene (~100 ppb), exhibited We values of 2020?g/g, 997?g/g, and 301?g/g for CNTs, C-X, and C-B, respectively. CNTs exhibited remarkably higher equilibrium adsorption values (We) than the Carbopacks, outperforming them by more than 2:1. Using the collected isotherms as a guide for empirical measurements, we determined the validity of models as applied to ?PCF performance. Using a ?PCF (filled with 1.2mg C-X) we observed decreased device performance for toluene with flow rates exceeding 10mL/min. With a flow rate of 15mL/min, the breakthrough volume (effective capture volume) decreased from 1.1L to 70mL.
Rebecca A. Veeneman was born in Cincinnati, Ohio in 1981. She graduated with an ACS certified B.S. in chemistry from Xavier University in 2003. While earning her undergraduate degree, she worked at the National Institute for Occupational Safety and Health developing multiple analytical methods for gas chromatography. These methods were published in the NIOSH Manual of Analytical Methods. She began her graduate career at the University of Michigan in 2003. Since passing her candidacy exam in 2005, Becki has been working in the Zellers group, testing and developing the preconcentrator module of the environmental sensors and subsystems thrust. Specifically, she is focusing on characterizing both commercial and novel materials and examining these materials in a more fundamental manner. With material knowledge in hand, she has been able to apply this experience to the micro-GC. She has been actively involved in the integration of Gen 0.6 and in the design of future generations, including Orion.