Insights into incipient soot formation by atomic force microscopy

Schulz, Fabian; Commodo, Mario; Kaiser, Katharina; Falco, Gianluigi De; Meyer, Gerhard; D’Anna, Andrea; Groß, Leo

doi:10.1016/j.proci.2018.06.100

Cited by 159 publications

(137 citation statements)

References 56 publications

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“…91 Furthermore, 18% of the structures include one or more rings with an odd number of C-atoms, leading to a stress in the graphitic plane and as a result to a more bend structure. This finding is consistent with other modeling studies, [92][93][94] as well as a recent atomic force microscopy study by Schulz et al 40 on soot precursors in the inception regime, showing that odd-numbered rings are found in nascent soot particles. In general, all features observed by Schulz et al, i.e.…”

Section: Resultssupporting

confidence: 93%

“…Additionally, a wide variety of structures could be generated having a large range of structural features, that could also be found in a structural study at the atomistic level. 40 This demonstrates that bond formation between PAH can lead to a variety of products and thus must be included into the modeling of soot inception and soot growth, as it would enable the description of the rampant growth of soot precursors that cannot be achieved by stepwise addition of smaller species to PAHs.…”

Section: Resultsmentioning

confidence: 99%

“…The formation of chemical bonds is also assumed in other models [34][35][36][37][38][39] to account for the high temperature soot inception and recent experimental studies support these findings. 40,41 Despite all these previous studies, several issues remain to be worked out and bond formation between soot precursors is not well understood. Nevertheless, in order to derive expressions for these chemical bond formations theoretical molecular modeling studies need to be performed.…”

Section: Introductionmentioning

confidence: 99%

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A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

et al. 2019

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In the present study bond formation reactions between soot precursors and their role in the soot inception process is investigated. The soot precursors were generated in macroscopic detailed gas-phase kinetic calculations and according to certain criteria introduced in simulation boxes to model bond formation between soot precursor molecules with reactive force field molecular dynamics modeling. The impacts of temperature, fuel mixture and equivalence ratio have been investigated on the rate and structure of the newly formed molecules. The resulting structures compare well to previously reported experimental results. Furthermore, the bond formation rate between PAH is found to be linearly correlated with the temperature at which the PAH precursors are generated, while fuel and equivalence ratio do not have a direct impact on the reaction rate. The generated growth structures are lumped in: 1) directly linked, 2) aliphatically linked and 3) pericondensed polycyclic hydrocarbons. It is found that the amount of aliphatically linked PAH increases with the amount of aliphatic content of fuel mixture. Finally, a reaction scheme is presented displaying the most representative reaction pathways to form growth structures in each lumping class and their eventual interconversion. The present work -that applies a combined approach of macroscopic gas-phase kinetic calculations and atomistic reactive force field simulations -offers a good alternative to obtain structural differences of nascent soot for a broad range of thermodynamic conditions and detailed reaction mechanisms for soot inception process.

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Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

et al. 2019

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“…It is known that as the building block of CNPs, PAHs have well-defined HOMO-LUMO gaps (28,29). The size of PAHs and their clustering and functionalization all impact the gap size (19,30,31). We illustrate some of these effects here by DFT calculations on homogeneous clusters of coronene and ovalene over the size range of 1-40 monomers.…”

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confidence: 95%

Flame-formed carbon nanoparticles exhibit quantum dot behaviors

Liu

Singh

Saggese

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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We examine the quantum confinement in the photoemission ionization energy in air and optical band gap of carbon nanoparticles (CNPs). Premixed, stretched-stabilized ethylene flames are used to generate the CNPs reproducibly over the range of 4-23 nm in volume median diameter. The results reveal that flameformed CNPs behave like an indirect band gap material, and that the existence of the optical band gap is attributed to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap in the polycyclic aromatic hydrocarbons comprising the CNPs. Both the ionization energy and optical band gap are found to follow closely the quantum confinement effect. The optical band gaps, measured both in situ and ex situ on the CNPs prepared in several additional flames, are consistent with the theory and the baseline data of CNPs from stretched-stabilized ethylene flames, thus indicating the observed effect to be general and that the particle size is the single most important factor governing the variation of the band gap of the CNPs studied. Cyclic voltammetry measurements and density functional theory calculations provide additional support for the quantum dot behavior observed. carbon nanoparticles | quantum dots | flames N anosized carbon grains composed of disordered polycyclic aromatic hydrocarbons (PAHs) are one of the most abundant forms of carbon material in nature (1). As a less-celebrated allotrope of carbon in comparison with fullerenes, nanotubes, and graphene, carbon nanoparticle (CNP) has its share of importance in a wide range of physical phenomena. Studies of interstellar emission spectra suggest that PAH dust grains or CNPs are ubiquitous in the interstellar media (2-5); and they are considered as the tracer of the star formation process (3, 6). CNPs are formed in flames during incomplete combustion. They are part of the soot-formation process. Mature soot or atmospheric black carbon particles often contain both elemental and organic carbon, the relative amounts of which vary by source (7). Soot impacts the global and region climate systems (8, 9) because of its light-absorbing properties (10, 11) and also as cloud condensation nuclei (12). CNPs 10-20 nm in size or fine carbon particles are themselves abundant in diesel exhausts (13). Their light-absorption properties and impact on climate forcing remain poorly characterized (14). As a material, however, CNPs have found their applications in photovoltaic and electrochemical devices, including perovskite solar cells in which flame CNPs act as a hole transfer medium (15).In contrast to the notion that soot, young or mature with respect to its growth in flames, is a broadband light absorber, recent studies have shown that CNPs several nanometers in size have well-defined optical band gaps or band edges (16)(17)(18). The band gap arises from the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the constituent PAHs (18,19). While previous studies (16-18) explored the vari...

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“…A large variety of mechanisms are expected to contribute to the formation of PAHs in the combustion of fossil fuels (Richter & Howard 2000;Moriarty & Frenklach 2000;Parker et al 2014;Kaiser et al 2015;Yang et al 2017), some of which are applied to astrochemistry to explain the formation of interstellar aromatic molecules in the outflows of carbon-rich stars (e.g., Frenklach & Feigelson 1989;Cherchneff et al 1992). The sequences of chemical reactions involved not only produce clean hexagon containing aromatic molecules, but they have also been shown in the laboratory to result in pentagon containing species (Bouwman et al 2015;Johansson et al 2018;Commodo et al 2019;Schulz et al 2019;McCabe et al 2020). Pentagon inclusion is also invoked to explain the formation of fullerenes through erosion of large PAHs as this provides a way to bowl the planar PAH plane (Berné & Tielens 2012).…”

Section: Introductionmentioning

confidence: 99%

Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)

Bouwman

Boersma

Bulak

et al. 2020

A&A

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Infrared bands at 3.3, 6.2, 7.6, 7.8, 8.6, and 11.2 μm have been attributed to polycyclic aromatic hydrocarbons (PAHs) and are observed toward a large number of galactic and extragalactic sources. Some interstellar PAHs possibly contain five-membered rings in their honeycomb carbon structure. The inclusion of such pentagon defects can occur during PAH formation, or as large PAHs are eroded by photo-dissociation to ultimately yield fullerenes. Pentagon formation is a process that is associated with the bowling of the PAH plane, that is, the ability to identify PAH pentagons in space holds the potential to directly link PAHs to cage and fullerene structures. It has been hypothesized that infrared (IR) activity around 1100 cm−1 may be a spectral marker for interstellar pentagons. We present an experimentally measured gas-phase IR absorption spectrum of the pentagon-containing rubicene cation (C26H14•+) to investigate if this band is present. The NASA Ames PAH IR Spectroscopic Database is scrutinized to see whether other rubicene-like species show IR activity in this wavelength range. We find that a specific molecular characteristic is responsible for this IR band. Namely, the vibrational motion attributed to this IR activity involves pentagon-containing harbors. An attempt to find this specific mode in Spitzer observations is undertaken and tentative detections around 9.3 μm are made toward the reflection nebula NGC 7023 and the H II-region IRAS 12063-6259. Simulated emission spectra are used to derive upper limits for the contributions of rubicene-like pentagonal PAH species to the IR band at 6.2 μm toward these sources.

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Insights into incipient soot formation by atomic force microscopy

Cited by 159 publications

References 56 publications

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

Flame-formed carbon nanoparticles exhibit quantum dot behaviors

Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)

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Insights into incipient soot formation by atomic force microscopy

Cited by 159 publications

References 56 publications

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

Flame-formed carbon nanoparticles exhibit quantum dot behaviors

Gas-phase infrared spectroscopy of the rubicene cation (C26H14•+)

Contact Info

Product

Resources

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Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)