CHAPTER 4. Raman, IR and INS Characterization of Functionalized Carbon Materials

Abstract

Vibrational spectroscopies represent a powerful tool to investigate the structural properties at an atomic level. In particular, the analysis of the spectra allows to have detailed information on both structure and chemical environment of different sites. Therefore, the spectroscopic characterization can usefully assist in the comprehension of the parameters ruling the unique catalytic properties of metal-free carbon materials, as well as to implement the knowledge in the design of new C-containing systems. Keeping in mind these purposes, the present Chapter tries to provide some insights on the information obtained by using vibrational spectroscopies to characterize carbonaceous materials. Intriguing and quite recently investigated systems will be illustrated as "case histories" to show what can be learned from the analysis of the spectra collected in different experimental conditions.The results concerning activated carbons, carbon nanotubes, graphene oxide as well as carbon nitrides or fullerenes will be discussed in order to investigate the effect of the pretreatment and of the functionalization/doping on the catalytic activity in different applications. Raman spectroscopy applied to carbonsRaman spectroscopy is based on the inelastic light scattering of a laser source in the near IR -UV range.Backscattered photons come out with a lower (ν 0 −ν vibr ) or higher (ν 0 +νvibr) energy with respect to the incoming laser photons (ν 0 ). The energy difference (ν vibr ) corresponds to the vibrational mode. A Raman active vibrational mode should involve a change in the electric polarizability. This powerful technique is widely adopted in the characterization of carbon derived materials, both crystalline [e.g. HOPG (highly oriented pyrolytic graphite), nano-graphite] or amorphous (e.g. turbostratic carbon, carbon fibers etc.). Raman spectroscopy of perfect and defective graphiteThe Raman spectrum of perfect graphite (e.g. HOPG) with large crystalline domains is dominated by a sharp peak centred at 1580 cm -1 (historically indicated as G peak, first order, see Figure 1a, top), which is attributed to a E 2g mode (Figure 1c, part A). In addition, a complex envelope of bands appears in the 2800-2600 cm -1 region (second order), mostly due to combination modes. In particular, two main peaks are observed in the spectrum of perfect graphite, originally indicated as G´2 (high frequency side, sharp) and G´1

All-Carbon Conductors for Electronic and Electrical Wiring Applications

“…Raman spectroscopy is one of the main analytical techniques that provide a detailed picture about chemical structure, phase, crystallinity and molecular interactions, not only of the CNTs and graphene sheets, but also of the final assembled fiber. A detailed description of CNT and graphene Raman features goes beyond the scope of this review and can be found elsewhere (Dresselhaus et al, 2010;Saito et al, 2011;Eckmann et al, 2012;Jain et al, 2017;Groppo et al, 2018). Among all fingerprints, the presence of the D-band at about 1350 cm −1 comes from double resonance Raman effect corresponding to disordered carbon structure, while the G-band (c.a.…”

Zeolite templated carbon from Beta replica as metal-free electrocatalyst for CO2 reduction

“…The convoluted band in the region 2960-2850 cm −1 was attributed to the asymmetric (2930 cm −1 ) and symmetric (2850 cm −1 ) stretching of C-H on sp 3 hybridized carbons [60] . The band shown at 1720 cm −1 can be assigned to C = O stretching in carboxylic aids, lactones and/or acid anhydrides [41] , although its position in aromatic structures can be affected by the presence of the different proximal groups [61] .…”

“…However, the study of the additional contribution of D , D and D * bands, obtained by deconvolution of Raman spectra, using a combination of four Lorentzian and one Gaussian functions allows a more in depth analysis of the degree of order in graphene based carbons [69] . D band (around 1620 cm −1 ) is attributed to the "graphene-like" layers or sp 2 nanostructures with a strained geometry [61] , D band (around 1500 cm −1 ), whose intensity is inversely proportional to crystallinity, is observed between the G and D band [70] . The D * band (around 1250 cm −1 ) is originated from the vibration of carbon sp 3 atoms that were restricted by oxygencontaining groups [69] .…”

From Polymer to Magnetic Porous Carbon Spheres: Combined Microscopy, Spectroscopy, and Porosity Studies

“…Raman spectra of magnetic carbon microspheres, obtained by means of three laser lines (785, 514, and 442 nm), are displayed in Figure 6. All the spectra are dominated by two intense bands, attributed to vibrational modes involving sp 2carbon species with a low sp 3 -carbon content commonly found in defective nanographitic crystallites (Ferrari and Robertson, 2000;Pimenta et al, 2007;Groppo et al, 2018). The signal around 1,600 cm −1 (G-band, E 2g symmetry), resulting from the in-plane bond stretching, is for a fact upward shifted of about 20 cm −1 with respect to the G-band of graphite, thus indicating that the stacking order of the sheets is very low and that the structure is also defective.…”

“…The amorphous nature of the carbon structure for both carbon materials is also well-supported by the observed IR absorption band in the 1,620-1,450 cm −1 range, with a maximum at about 1,570 cm −1 (Supplementary Figure 4, left panel). Such IR band is, for a fact, associated with presence of double-conjugated C vibrational modes (ν C=C ) in sp 2 carbons in presence of defects (i.e., surface terminations, heteroatoms, functional groups, radical species, where there is a change of the dipole moment (in contrast to what observed in graphitic carbon materials, more ordered domains) (Jain et al, 2017;Groppo et al, 2018).…”