Characterization of Black Carbon using NEXAFS Spectroscopy.

 Abstract

            Black carbon (BC) is commonly characterized along a continuum of chemical and physical properties. To delineate BC from other forms of carbon (C) comprising organic samples such as soils and sediments, researchers have attempted to define specific chemical properties as criterion for inclusion as BC, however, precise boundaries may be difficult to attain due to the compositional changes occuring from chemical and physical separation techniques. We used synchrotron-based C (1s) Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to explore the C K-edge of BC reference materials (laboratory produced BC, environmental matrices, potential interference materials) without prior chemical or physical separation. Spectra were deconvoluted to determine percentages of specific functional C groups. Multiple C(1s) transitions in the fine structure of the C NEXAFS region (284-290 eV) representing aromatic C, phenolic-C, aliphatic C, carboxylic C, and O-alkyl C were used to characterize and contrast different types of BC reference materials. N-hexane soot and chars were characterized by the predominance of an aromatic peak at 285 eV and absence of other features. Chars spectra indicated the recalcitrance of plant components such as lignins or waxes evident in features at 286.1 eV, a signature not detected in other reference materials. Deconvolution showed large proportions of aromatic C comprising chars, soot and bituminous coal compared with other reference materials. Aromaticity of BC was the main distinguishing factor for BC from environmental matrices and potential interference products.