# Multigraphene Prepared by One-Pot Pyrolysis of Diatomite/Polypropylene Composites
## 3 Results and Discussion
Figure 2a shows the influence of the DM content on the graphene yield via the pyrolysis of the DM/PP composites at 1000 \({}^{\circ}\)C. When the DM content was not more than 30 wt.%, the graphene yield (G\({}_{\text{a-1000}}\)) demonstrated an obvious increase with DM content, which was attributed to there being more interface area between DM and PP. The highest yield  
Figure 1: SEM image of products obtained via the pyrolysis of (**a**) pure DM and (**b**) commercial PP chips containing 0.1 wt.% DM with an inset showing the EDXA spectrum; (**c**) TEM image, (**d**) HRTEM image, (**e**) thickness distribution, (**f**) PXRD pattern, (**g**) Raman spectra, and (**h**) XPS spectra of purified products obtained by pyrolysis of commercial PP chips containing 0.1 wt.% DM. (25.86%) was gained from DM/PP-30 and was higher than that observed in other reported methods [30; 36]. However, when the content increased further, the yield decreased slightly, which could be the result of the large amount of DM congregation in the composites and the reduced interface area, leading to a reduction in the catalytic efficiency. The Raman spectra of G\({}_{\text{a-1000}}\) (not presented here) were similar to those of the products obtained from the commercial PP chips (Figure 1g), indicating that the DM content had little effect on the graphene structure. The pyrolysis temperature is another main factor affecting graphene formation. When the temperature was less than 800 \({}^{\circ}\)C, no graphene was obtained. Figure 2b displays the yields of the graphene products obtained by pyrolysis of DM/PP-20 under different pyrolysis temperatures. It can be observed that the yield greatly increased from 8.10% to 16.25% as the temperature increased in the region of 850-950 \({}^{\circ}\)C. When the temperature increased further (1000-1100 \({}^{\circ}\)C), the graphene yield (G\({}_{\text{20-b}}\)) decreased, something that was attributed to graphene's decreased nucleation density at higher temperatures. These results are consistent with the results that were previously reported in the literature [37; 38]. Thus, higher temperatures do not facilitate graphene formation [39]. The influence of temperature on the structure of G\({}_{\text{20-b}}\) was further explored by the Raman spectra (Figure 2c,d). When the temperature was 850 \({}^{\circ}\)C, there was a poor 2D characteristic peak, indicating that growth was still not complete. After further increasing the temperature from 850 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C, the D/G intensity ratio decreased and the 2D/G intensity ratio increased, implying the formation of graphene with a small number of layers with few structural defects [40]. The smallest I\({}_{\text{D}}\)/I\({}_{\text{G}}\) (0.68) and highest I\({}_{\text{2D}}\)/I\({}_{\text{G}}\) (0.39) were obtained at 1000 \({}^{\circ}\)C, which was ascribed to the high degree of graphitization. When the temperature was 1050 \({}^{\circ}\)C and 1100 \({}^{\circ}\)C, the I\({}_{\text{D}}\)/I\({}_{\text{G}}\) ratio and I\({}_{\text{2D}}\)/I\({}_{\text{G}}\) ratio were 0.74 and 0.79 and 0.32 and 0.18, respectively. This clearly shows the increase in the I\({}_{\text{D}}\)/I\({}_{\text{G}}\) ratios and the decrease in the I\({}_{\text{2D}}\)/I\({}_{\text{G}}\) ratios, which is suggestive of the increased thickness of the as-grown graphene layer as well as more defects. This phenomenon may be caused by the reduced concentration of active carbon species and graphene's increased nucleation rate  
Figure 2: (**a**) Effects of DM content on the yield of G\({}_{\text{a-1000}}\); (**b**) effects of pyrolysis temperature on the yield of G\({}_{\text{20-b}}\); (**c**) Raman spectra of G\({}_{\text{20-b}}\); (**d**) effects of pyrolysis temperature on I\({}_{\text{D}}\)/I\({}_{\text{G}}\) and I\({}_{\text{2D}}\)/G ratios of G\({}_{\text{20-b}}\). over 1000 \({}^{\circ}\)C [41; 42]. Therefore, the graphene structure was significantly affected by the pyrolysis temperature.