Photochemically induced decarboxylation in diesel soot extracts

Aqueous extracts from diesel engine exhaust particulate matter (soot) obtained by hot pressurized water extraction were subject to near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with respect to the carbon K (1 s) absorption edge at a synchrotron radiation source. The highly intense X-ray beam caused a significant decrease of the carboxyl peak intensity at 288 eV, to the benefit of a newly arising carbonate peak at 291.2 eV. The same phenomenon was found in alginic acid when exposed to the same conditions. With knowledge of the molecular structure of alginic acid, we are able to propose a simple photochemical reaction scenario that describes a decay path for carboxyl in soot: the radiolysis of carboxylate into carbonate in diesel soot during irradiation.