Structural analysis of char by Raman spectroscopy: Improving band assignments through computational calculations from first principles
| Autor: | Matthew Smith, Jean-Sabin McEwen, Juan F. Espinal, Carolyn S. Brauer, Manuel Garcia-Perez, Ian Dallmeyer, Timothy J. Johnson |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Materials science
Chemistry(all) Analytical chemistry 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Coronene 0104 chemical sciences chemistry.chemical_compound symbols.namesake chemistry Vacancy defect Molecular vibration symbols Molecule Organic chemistry General Materials Science Density functional theory Char 0210 nano-technology Raman spectroscopy Pyrolysis |
| Zdroj: | Carbon. 100:678-692 |
| ISSN: | 0008-6223 |
| DOI: | 10.1016/j.carbon.2016.01.031 |
| Popis: | The complex heterogeneous nature of chars has confounded the complete analysis of the Raman spectra of these materials. The additional shoulders observed on the defect (D)-band and high intensity valley between the D and graphitic (G)-bands represent the primary regions of uncertainty. In this paper the effects of various vacancy and substitution defects in a coronene parent molecule have been systematically analyzed using density functional theory (DFT). The impacts of these defects are best understood in terms of a reduced symmetry as compared to a “parent” coronene molecule. Based on simulation results, a total of ten potential bands have been assigned between 1000 cm −1 and 1800 cm −1 . These bands have been used to deconvolute a thermoseries of cellulose chars produced by pyrolysis at 300–700 °C. The shoulder observed in chars near 1200 cm −1 has been assigned to the symmetric breathing mode of various small polyaromatic hydrocarbons (PAH) as well as rings containing seven or more carbons. Intensity between 1400 cm −1 and 1550 cm −1 results from a range of coupled vibrational modes from various defect structures. The deconvolution of cellulose derived chars shows consistent growth of PAH clusters, loss of oxygen, and development of non-hexoganal ring systems as pyrolysis temperature increased. |
| Databáze: | OpenAIRE |
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