The interpretation of C1s XPS spectra from disordered oxygenated carbons remains uncertain despite a variety of schemes reported in the literature. Here, a thermoseries of cellulose chars was studied to evaluate six published deconvolution schemes; however, none were capable of correctly identifying the oxygen content determined by the O1s spectrum. To improve the self-consistency of the XPS interpretation a method is proposed based on a 7 peak C1s deconvolution, 3 C-C peaks, 3 oxygenated peaks, and pi-pi* transition peak. Deconvolution of the O1s by 4 peaks is used to determine O-C and O=C contributions which provide upper and lower bounds for the related C1s peaks: C-O, C=O and COO. To improve assignments, various functional groups and carbon structures have been examined via DFT using an initial state approximation. DFT calculations of model compounds (pyrene, cellobiose and peryelene tetracarboxylic dianhydride (PTCDA)) were compared with experimental results to confirm the validity of the calculation method used. The DFT calculations identified several defect structures that justify the use of 3 peaks for deconvolution of the C-C region of C1s XPS spectra. The deconvolution method proposed provides C:O ratios in good agreement (within 5 %) of those obtained from total C1s and O1s peaks.

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.

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Reaction of CO with carbonaceous surfaces was investigated using B3LYP density functional theory level (DFT) with the 6-31G(d) basis set. It was found that CO can be adsorbed exothermically on the active sites of zigzag, armchair, and tip carbonaceous models to yield stable intermediates such as cyclic ether, carbonyl, lactone, ketone, carbonate, and semiquinone functionalities. The above reactions are important in carbon gasification processes as well as in carbon single-wall nanotubes formation from CO disproportionation reaction. In the case of gasification, adsorption of CO blocks the active sites of the carbonaceous material and thus can reduce the efficiency of the process. Furthermore, it was found that when CO is adsorbed in a carbonyl type structure (CdCdO), there is a reversible interconversion process by ring closure with a neighbor active site to produce a cyclic ether (furan type), a process that requires an additional neighboring active site. Consequently, the available number of active sites for gasification reaction is decreased and therefore the gasification reaction is inhibited. In addition, CO adsorption on oxidized surfaces can favor CO 2 desorption. Such desorption can be either taking off an oxygen atom that potentially was going to be desorbed as CO or depositing a carbon atom on the surface due to the disproportionation reaction 2 CO ) C + CO 2 . Both effects can inhibit or retard the gasification process. The results from the disproportionation reaction can also provide an insight into the mechanism for carbon single-wall nanotubes growth using CO as precursor.