Structural analysis of char by Raman spectroscopy: Improving band assignments through computational calculations from first principles

作者：Smith, Matthew W.; Dallmeyer, Ian; Johnson, Timothy J.; Brauer, Carolyn S.; McEwen, Jean-Sabin^*; Espinal, Juan F.; Garcia-Perez, Manuel^*

来源：Carbon, 2016, 100: 678-692.

DOI：10.1016/j.carbon.2016.01.031

• POLYCYCLIC AROMATIC-HYDROCARBONS
• SCALING FACTORS
• FAST PYROLYSIS
• BASIS-SETS
• CARBON
• BIOCHAR
• SPECTRA
• GRAPHITE
• C-70
• CARBONIZATION

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 degrees 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.

• 出版日期2016-4