PAH structure analysis of soot in a non-premixed flame using high-resolution transmission electron microscopy and optical band gap analysis

Botero, María L.; Adkins, Erin M.; González-Calera, Silvia; Miller, Houston J.; Kraft, Markus

doi:10.1016/j.combustflame.2015.11.022

Cited by 75 publications

(56 citation statements)

References 76 publications

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“…In comparison to young PMX soot, as found in previous work [45,53], the spectrum of mature soot shows wider D and G peaks and a higher I(D)/I(G) ratio ( Also, the optical band gap values measured on the UV-Vis spectra of IDF and young PMX soot appear similar and higher (0.5-0.7eV) than that evaluated for mature PMX soot (about 0.2) (Table 1). However, such Eg values are still closer to the band gap value of graphite (Eg=0eV) than to the Eg values of four-to seven-ten ring PAH (>2eV), and consequently, are in contradiction with the soot structural model based on small-to medium-size PAH as main elementary units of soot [45,[47][48][49][50][51][52][53]. Besides, the Eg values of soot are much lower in respect to the Eg of PAH, typically detected in the organic carbon, underlining the discontinuity already found between the UV-Vis spectra of organic carbon and black carbon constituting the combustion aerosol [67].…”

Section: Resultsmentioning

confidence: 59%

“…Moreover, large aromatic layer lengths are in contrast with the vision of the soot internal structure as constituted of small polyaromatic layers, instead characterized by high band gaps (2-4 eV) [41,46], more or less (turbostratically) stacked together. This model of soot structure has been postulated on the basis of chemical [47] and modeling [48] works, and also, more recently derived from HRTEM [45,[49][50][51] and Raman [45,52,53] measurements.…”

Section: Introductionmentioning

confidence: 99%

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Optical properties of organic carbon and soot produced in an inverse diffusion flame

Russo

Apicella

Lighty

et al. 2017

Carbon

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The carbonaceous matter (soot plus organic carbon) sampled downstream of an ethylene inverse diffusion flame (IDF) was chemically and spectroscopically analyzed in detail. In particular, the H/C ratio, the UV-Visible absorption coefficient and Raman parameters were measured and found to be representative of a highly disordered sp 2-rich carbon as the early soot sampled in a premixed flame. In contrast, the optical band gap was found to be relatively low (0.7eV), closer to the optical band gap of graphite than to that of medium-sized polycyclic aromatic hydrocarbons (>2eV) which are widely considered to be soot precursors and are mostly contained in the organic carbon. The significance of the optical band gap as signature of different structural levels (nano-, micro-and macro-structure) of sp 2-rich aromatic disordered carbons was critically analyzed in reference to their molecular weight/size distribution. The relevance of the optical band analysis to the study of the soot formation mechanism was also highlighted.

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Section: Resultsmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Optical properties of organic carbon and soot produced in an inverse diffusion flame

Russo

Apicella

Lighty

et al. 2017

Carbon

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“…Once curvature is integrated, significant electric polarisation of the molecule occurs [10]. For the size of fragments found in primary soot particles determined from HRTEM and optical band gap methods (10-20 rings) [11] we predicted a range of 4-6.5 debye (which is two to three times that of water; 1.85 debye [12]) [10]. Figure 1 shows the electric potential around water, corannulene and coronene.…”

Section: Introductionmentioning

confidence: 87%

Polar curved polycyclic aromatic hydrocarbons in soot formation

Martin

Bowal

Menon

et al. 2019

Proceedings of the Combustion Institute

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Recent experimental and computational work suggests that a significant number of curved aromatic molecules are found in carbon materials such as soot. These curved aromatic molecules contain a substantial dipole moment (4-6.5 debye for the sizes seen in soot molecules containing 10-20 rings). In this paper we employ electronic structure calculations to determine the earliest onset of curvature integration. We found an interplay between the σ bonding inducing curvature and the π bonding resisting curvature with a size of six rings, with at least one being pentagonal, required to curve an aromatic molecule. The interactions between polar curved arenes and other species are then considered with particular focus on nascent soot formation, indicating that heterogeneous, not homogeneous, nucleation could be a significant factor in soot formation.

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“…The physical structure of soot freshly emitted from flames has been characterized as fractal aggregates, with radii of gyration on the order of 100–400 nm, and composed of primary particles (PP) with diameters on the order of 10–50 nm . Within these PP, high resolution TEM reveals disordered stacks with fringe lengths on the order of 1 nm and fringe spacing approximately that of graphite (0.35 nm) . Experimentally, greater challenges are presented by the intermediate stages of this process, particularly approaching the transition from two‐ to three‐dimensional structures.…”

Section: Introductionmentioning

confidence: 99%

The Molecular Composition of Soot

et al. 2020

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Soot (sometimes referred to as black carbon) is produced when hydrocarbon fuels are burned. Our hypothesis is that polynuclear aromatic hydrocarbon (PAH) molecules are the dominant component of soot, with individual PAH molecules forming ordered stacks that agglomerate into primary particles (PP). Here we show that the PAH composition of soot can be exactly determined and spatially resolved by low‐fluence laser desorption ionization, coupled with high‐resolution mass spectrometry imaging. This analysis revealed that PAHs of 239–838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. As informed by chemical graph theory (CGT), the vast majority of species observed in the sampled particulate matter may be described as benzenoids, consisting of only fused 6‐membered rings. Within that limit, there is clear evidence for the presence of radical PAH in the particulate samples. Further, for benzenoid structures the observed empirical formulae limit the observed isomers to those which are nearly circular with high aromatic conjugation lengths for a given aromatic ring count. These results stand in contrast to recent reports that suggest higher aliphatic composition of primary particles.

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PAH structure analysis of soot in a non-premixed flame using high-resolution transmission electron microscopy and optical band gap analysis

Abstract: Soot particles formed in a system of non-premixed liquid fuel flames supported on a wick-fed, smoke point test burner (ASTM D1322-08) were characterised by in-situ visible light extinction and thermophoretically-sampled high-resolution transmission electron microscopy measurements, HRTEM.

Cited by 75 publications

References 76 publications

Optical properties of organic carbon and soot produced in an inverse diffusion flame

Optical properties of organic carbon and soot produced in an inverse diffusion flame

Polar curved polycyclic aromatic hydrocarbons in soot formation

The Molecular Composition of Soot

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