In Situ and Time Resolved Carbonaceous Matter Oxidation Studies with Indirect Nanoplasmonic Sensing
Examensarbete för masterexamen
Applied physics (MPAPP), MSc
This work aims at assessing the oxidation of carbonaceous matter with a novel optical experimental technique named Indirect Nanoplasmonic sensing (INPS). The INPS working principle is based on the optical absorption profile of metallic nanoparticles via the excitation of localized surface plasmon resonances and was, in this work, utilized for the first time to monitor in situ and in real time un-catalyzed O2-based oxidation of nanoscopic carbon materials. Oxidation of carbon-based materials is central in a wide range of industrial applications as well as in energy production based on fossil fuels, and in environmental cleanup processes. In particular, under the category of transport emission reduction in the process of regenerating Diesel Particulate Filters (DPF), under-standing the oxidation reaction of carbonaceous matter known as soot is of high importance in order to meet more and more stringent emission legislations, which are imposed due to the health risks associated with soot nanoparticles. Two types of carbonaceous matter were used in this study, Printex U commonly used as a model for diesel soot and graphitized carbon films in the main part of the project. The Printex U study, due to the problems mainly associated with deposition on INPS sensor chips, turned out to require efforts beyond the scope of this work to derive an optimal deposition protocol and is thus only discussed in the appendix. INPS showed in general a high sensitivity towards oxidation rates of graphitic carbon films as a function of temperature and oxidant concentration. From progressive isothermal oxidation experiments, relevant kinetic parameters could be extracted, such as an activation energy of around 135 kJ/mol. Differential and pulsed oxidation experiments were used to extract the reaction order, which was found to be 1 for oxygen. Both these values are in agreement with the range of reported values in the literature. In connection to the reactivity of carbon films, conversion dependencies were assessed and found to agree well with previous published results. Finally, also the oxidation history of the carbon films, that is to what oxidation conditions the films have been exposed previously, was shown to be important as it modifies the rate of the further oxidation. Due to the complexity of the carbon oxidation process (e.g. sites with different reactivities, timedependent number of active sites, etc.), and due to issues originating arguably from the chosen deposition procedure of the carbon films (i.e. thermal evaporation), a high degree of reproducibility for the progressive isothermal oxidation experiments could not achieved. In connection to the INPS platform, due to the fact that sensitivity of plasmonic signal is a function of several parameters such as temperature, distance of the reaction from the sensor surface and more, the comparison of the different temperature results and different film thicknesses are subject to limitations. Possible improvements to eliminate/minimize such effects are thus also discussed.
Fysik , Physical Sciences