# On the Stability of Graphene-Based Aqueous Dispersions and Their Performance in Cement Mortar
## 3 Results and Discussion
### Raman Spectra  
Graphene-based materials exhibit exceptional functional properties, making them an extremely promising nanoscale additive for enhancing the multifunctionality of concrete composites [22; 23]. However, to preserve graphene's full potential in cementitious  
Figure 2: FESEM analyses on as-received Gr-TG fragments: (**a**) magnification 2000\(\times\); (**b**) multi-layered region with some typical dimensions, magnification 120,000\(\times\); (**c**) magnification 300,000\(\times\) of a few layered region. FESEM analyses on as-received GO fragments: (**d**) magnification 2000\(\times\); (**e**) magnification 120,000\(\times\); (**f**) magnification 240,000\(\times\).  
materials, a significant challenge must be overcome: achieving uniform dispersion of the nanosheets without compromising their quality. This challenge remains a key research focus because graphene has an intrinsic tendency to agglomerate due to van der Waals interactions within planes, at the expense of the cement matrix mixture's uniformity. Consequently, various mechanical mixing/agitation and chemical modification techniques have been developed to uniformly disperse graphene within the cementitious matrix, ensuring its nanoscale properties are fully utilised [3; 50].  
In the present work, to assess the quality of graphene additives and the effect of subsequent treatments, Raman spectra were systematically acquired. In Figure 3a, representative results are reported for: as-received Gr-TG (gray line); D-TGb (after HT), not sonicated dispersion (red line); and D-TGb after HT and LPE (blue line).  
All the spectra reported in Figure 3a exhibit the G peak (1581 cm\({}^{-1}\)), which arises from a first-order process activated by an iTO or iLO phonon with q = 0 momentum and is typical of graphene-based materials. The 2D mode, typically centered at about 2700 cm\({}^{-1}\), is associated with a second-order process involving two iTO phonons with opposite momenta at the border of the Brillouin zone and is linked to the breathing of the hexagonal mesh of graphene. The 2D band's overall shape (located at 2703 cm\({}^{-1}\) and with a full width at half maximum of (74.19 \(\pm\) 0.98) cm\({}^{-1}\) for Gr-TG) and the ratio relative to the G band, point to the conclusion that the utilized additive is turbostratic graphene [51; 52]. In the same region of the spectrum, as highlighted in the inset of Figure 3a, the Gr-TG and the D-TGb (HT) completely overlap. On the other hand, after sonication, the D-TGb (HT+LPE) suspension shows an enhanced intensity of the 2D band of about 11%, suggesting a partial degree of exfoliation [53]. The existence of the D band (1349 cm\({}^{-1}\)), related to a second-order process, is pronounced in all the spectra and indicates the presence of planar and edge defects in the graphene sheets, while its intensity is related to the nanosheet size [53].  
In Figure 3b, Raman spectra of as-received GO (gray) and D-GOb dispersion (red) after LPE, are shown. GO spectrum exhibits the D peak (1341 cm\({}^{-1}\)) intensity slightly higher than the G one (1588 cm\({}^{-1}\)) with a relative I\({}_{D}\)/I\({}_{G}\) ratio of 1.16, indicating that the material presents many defects due both to the defective and disordered surface, given by the high carbon/oxygen ratio (see Table 1) [54] and edges [55]. After sonication, slight changes are observed in the spectrum, including an I\({}_{D}\)/I\({}_{G}\) ratio increment of about 4%.  
Figure 3: Raman spectra of: (**a**) as-received Gr-TG (grey line); D-TGb dispersion after HT treatment (red line); D-TGb dispersion after HT and LPE treatments (blue line). In the inset, a zoom-up of 2D bands with their relative intensity is reported. (**b**) Raman spectra of D-GOb (red line) and as-received GO (black line). For each sample, twenty spectra were acquired in different regions. Background subtraction and normalisation to the G peak were applied, then an average was calculated among the resulting spectra.