# Multigraphene Prepared by One-Pot Pyrolysis of Diatomite/Polypropylene Composites
## 3 Results and Discussion  
Commercial PP chips with 0.1 wt.% DM were unintentionally pyrolyzed under the pyrolysis temperature of 1000 \({}^{\circ}\)C and at a growth time of 100 min, and the obtained products were collected and characterized. Unlike the pure DM, there was a layer with several wrinkles on the surface of the products (Figure 1a,b), which indicated that something had formed during pyrolysis. The elemental composition analysis of this layer was performed via EDXA during the SEM measurement process. The EDXA spectrum (Figure 1b inset) showed well-defined C, O, and Si peaks in the products and further confirmed the formation of something on the DM, while the DM only contained Si and O. After DM removal, typical folded sheets were observed, as shown in Figure 1c. The HRTEM images revealed that the sheets were composed of 4 to 6 layers and that the interlayer spacing of these layers was about 0.336 nm (arrows in Figure 1d), which was consistent with that of graphite. Meanwhile, the diffraction pattern of these obtained sheets (Figure 1d inset) displayed a hexagonal crystalline structure, providing clear evidence of the graphene layer. Further statistical analysis was carried out based on the HRTEM images of 20 arbitrarily selected sheets. As seen in Figure 1e, the thickness distribution indicates a yield of \(\sim\)95% (\(\leq\)10 layers) and an average layer number of 4.6. In addition, the estimated average lateral size of the graphene flake was approximately 22 \(\upmu\)m due to the size of the as-grown graphene flake (Figure S1), which were dependent on the size of the DM. Figure 1f displays the PXRD pattern of the as-prepared graphene layer. Diffraction peaks, (002) at 25.9\({}^{\circ}\) and (10), (100) at 41.9\({}^{\circ}\), can be observed, and these peaks correspond to the hexagonal graphite structure and the combination of turbostratic graphite and crystalline graphite, respectively [32]. The d-spacing of the (002) peak corresponds to an interlayer spacing of 0.34 nm, which was consistent with the HRTEM results. The average number of graphene layers per stack (n) could be calculated by the Bragg equation and Scherrer formula [33,34]. The value n of the synthesized graphene was about 2.7, indicating that most of the graphene with only a few layers formed during the pyrolysis and that the layer number was less than that determined by other reported methods [25,35], a finding that is in good accordance with the HRTEM results that were previously observed (Figure 1d,e). The Raman spectra (Figure 1g) showed three peaks at 1335 cm\({}^{-1}\), 1569 cm\({}^{-1}\), and 2682 cm\({}^{-1}\), corresponding to the D band (structural defects and partially disordered structures of the sp\({}^{2}\) carbon), G band (first-order scattering of the E\({}_{\text{2g}}\) vibrational mode of the sp\({}^{2}\) carbon), and 2D band (second-order vibration caused by the scattering of phonons at the zone boundary), respectively. The intensity ratio of peak D to peak G (I\({}_{\text{D}}\)/I\({}_{\text{G}}\) = 0.70) indicated the few presence of disordered and randomly arranged graphene sheets in the products. The intensity ratio of 2D peak to G peak (I\({}_{\text{2D}}\)/I\({}_{\text{G}}\) = 0.72) implied that the products only had a small number of graphene layers, which was in accordance with the HRTEM and PXRD results (Figure 1d,f). XPS measurements were used to further investigate and characterize the defects of the structure. The results showed that graphene surface mainly consisted of carbon elements (94.39 wt.%) and oxygen (5.61 wt.%). The XPS spectra of the C1s were curve-fitted into three individual peaks (Figure 1h): the graphitic carbon (284.6 eV), C-OH (285.6-285.8 eV), and C=O (286.6-286.8 eV) peaks. The chemical component and oxidation state of carbon were mainly graphitic carbon (84.2%), C-OH (12.4%), and small amounts of C=O (3.4%).