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C 1s K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy for characterizing functional group chemistry of black carbon


Heymann, K; Lehmann, J; Solomon, D; Schmidt, M W I; Regier, T (2011). C 1s K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy for characterizing functional group chemistry of black carbon. Organic Geochemistry, 42(9):1055-1064.

Abstract

Black carbon (BC) is considered ubiquitous in soil organic matter (OM) and therefore plays an important role in soil biogeochemistry. Its complexity, particularly within environmental matrices, presents a chal- lenge for research, primarily as a result of techniques which may favor detection of certain functional group types rather than capturing total sample C. The objective of this study was to utilize carbon (C) 1s near edge X-ray absorption fine edge structure (NEXAFS) spectroscopy to characterize the C chemistry of a broad range of BC materials. Characteristic resonances in the NEXAFS spectra allowed direct molec- ular speciation of the total C chemistry of the reference materials, environmental matrices and potentially interfering materials, obtained from an earlier BC ring trial. Spectral deconvolution was used to further identify the functional group distribution of the materials. BC reference materials and soils were charac- terized by a large aromatic C region comprising around 40% of total absorption intensity. We were able to distinguish shale and melanoidin from BC reference materials on the basis of their unique spectral char- acteristics. However, bituminous coal shared chemical characteristics with BC reference materials, namely high aromaticity of more than 40% identified by way of a broad peak. Lignite also shared similar spectra and functional group distributions to BC reference materials and bituminous coal. We compared the results of spectral deconvolution with the functional group distributions obtained by way of direct polarization magic angle spinning (DPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy. Corre- lations between aromatic type C values for DPMAS 13C NMR and NEXAFS gave r2 = 0.633 (p < 0.05) and the values for NEXAFS were around 30–40% lower than for 13C NMR. Correlations were also drawn between the aromatic C/O-alkyl C ratio values for the two methods (r2 = 0.49, p < 0.05). Overall, NEXAFS was applicable for a wide range of environmental materials, such as those measured, although some lim- itations for the technique were addressed.

Black carbon (BC) is considered ubiquitous in soil organic matter (OM) and therefore plays an important role in soil biogeochemistry. Its complexity, particularly within environmental matrices, presents a chal- lenge for research, primarily as a result of techniques which may favor detection of certain functional group types rather than capturing total sample C. The objective of this study was to utilize carbon (C) 1s near edge X-ray absorption fine edge structure (NEXAFS) spectroscopy to characterize the C chemistry of a broad range of BC materials. Characteristic resonances in the NEXAFS spectra allowed direct molec- ular speciation of the total C chemistry of the reference materials, environmental matrices and potentially interfering materials, obtained from an earlier BC ring trial. Spectral deconvolution was used to further identify the functional group distribution of the materials. BC reference materials and soils were charac- terized by a large aromatic C region comprising around 40% of total absorption intensity. We were able to distinguish shale and melanoidin from BC reference materials on the basis of their unique spectral char- acteristics. However, bituminous coal shared chemical characteristics with BC reference materials, namely high aromaticity of more than 40% identified by way of a broad peak. Lignite also shared similar spectra and functional group distributions to BC reference materials and bituminous coal. We compared the results of spectral deconvolution with the functional group distributions obtained by way of direct polarization magic angle spinning (DPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy. Corre- lations between aromatic type C values for DPMAS 13C NMR and NEXAFS gave r2 = 0.633 (p < 0.05) and the values for NEXAFS were around 30–40% lower than for 13C NMR. Correlations were also drawn between the aromatic C/O-alkyl C ratio values for the two methods (r2 = 0.49, p < 0.05). Overall, NEXAFS was applicable for a wide range of environmental materials, such as those measured, although some lim- itations for the technique were addressed.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2011
Deposited On:25 Nov 2011 10:00
Last Modified:05 Apr 2016 15:07
Publisher:Elsevier
ISSN:0146-6380
Publisher DOI:10.1016/j.orggeochem.2011.06.021
Permanent URL: http://doi.org/10.5167/uzh-51262

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