FTIR quantification of the functional C groups in coals and extraterrestrial kerogens: a calibration procedure
2019
Kerogensand coals are complex polyaromatic carbonaceous solids that formed in Earth sediments from the thermal maturation and preservation of living organisms[1].
Kerogen-like polyaromatic materials are also present in primitive
meteorites, presumably formed in the proto-solar disk through thermal and/or radiolytic reactions and were further processed in their
parent bodies[2]. Though decades of analytical investigations, the composition and chemical structure of those materials remain not fully elucidated. FTIR (Fourier-Transform Infrared Spectros-copy) has been proved to be a powerful technique for characterizing coals, peats, terrestrial and
meteoritic
kerogens[2]–[4]. However, the quantification of functional C groups by calculating of the integrated cross-section of each functional C groups is hampered by the lackof precise knowledge of their integrated cross-sections. Our present workaims to investigate the infrared spectra usingthe different standards as known polymers [5]and synthetic polyaromatic materials(e.g.
tholin), produced by thermal degradations of a 13C-substituted precursor. It was synthesized in a cold plasma reactor(PAMPRE, Latmos, Guyancourt) from a 13CH4: 13CO = 7: 3 gas mixture with 90% of Ar [6]. Characterization of known molecular polymer and the carbonized
tholinwere performed and Nuclear Magnetic Resonance(NMR)measurements were then run, providing estimates of the integrated cross-sections ratio of the aromatic, C=C, C=O and CHxgroups. The carbonizationprocess canincrease the polyaromatic characterin the
tholincompositiontoward a structure similar to that observed in these terrestrial and
extraterrestrial materials. We will present the whole calibration procedure and applications to the quantification of the above-mentioned functional groups for coal and
meteoritic
kerogensamples. A series of coalswith different
vitrinitereflectancesand some FTIR data of IOM samples from chondrites will be re-calculated to compare with the previous data to see the contribution of the relative abundance of carbon atoms
regradingto the C=C, C=O, CH3, CH2and aromatic groups
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