Improving the deconvolution and interpretation of XPS spectra from chars by ab initio calculations

Abstract

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.

Bifunctional Solid Catalyst for Organic Reactions in Water: Simultaneous Anchoring of Acetylacetone Ligands and Amphiphilic Ionic Liquid “Tags” by Using a Dihydropyran Linker

“…The two predominant peaks at 533.4 and 532.8 eV were characteristic of the HMS backbone and its OH groups, whilst the peaks at about 532.5 eV were attributed to the O−C species of the silicane coupling agent . The other peaks at 531.8 eV, with a lower intensity, corresponded to C=O groups, in agreement with the FTIR results . In the XPS pattern of the C 1s region, contributions of the C−O/C−S (286.6 eV), C=O (288.8 eV), C−C (285.1 eV), C=C (284.5 eV), and C−N (285.8 eV) bonds were all observed, as expected …”

Surface‐Group‐Oriented, Condensation Cyclization‐Driven, Nitrogen‐Doping Strategy for the Preparation of a Nitrogen‐Species‐Tunable, Carbon‐Material‐Supported Pd Catalyst

“…The most intense C1s peak located at 284.66 eV can be assigned to the sp 2 ‐hybridized graphitic carbon (C=C) originated from the activated carbon skeleton. And the peaks centered at ∼288.70 eV, ∼287.30 eV and ∼286.30 eV assigned to the C=O, O−C=O and C−O groups respectively, appear in all samples . The intensity of these peaks indicates the existence of trace amounts of oxygen species.…”

“…And the other is that the peak at ∼285.35 eV presents inconsistent shifts among Pd/NC(pretreated)s, compared with Pd/AC(pristine). The peak at 285.2∼285.4 eV in C1s spectra (Figure a–e) can be assigned to sp 3 ‐hybridized carbon (C−C), on the other hand, it can also be defined as C−N group due to the disordering of graphite‐like structure after embedding N atoms into carbon skeleton . In fact, it is a bit difficult to specifically characterize the peak of C−C or C−N, however some positive changes can be still observed.…”

Activated carbons for applications in catalysis: the point of view of a physical-chemist

“…Very recently, this deconvolution method has been improved by Smith et al (Smith et al 2016), by adding a peak near 285 eV to account for defective species.…”

“…intrinsic conducting or semiconducting behavior of the samples). For these reasons, the number of peaks used to fit C 1s XPS spectra of carbon based materials can vary considerably (Biniak et al 1997;Blume et al 2015;Chen et al 2008;Jeong et al 2008;Langley et al 2006;Lopez et al 1991;Smith et al 2016). An additional source of incomprehension is the choice of the photon source that affects the observed line shapes.…”