# Facile Preparation of Multilayered Graphene with CO\({}_{2}\) as a Carbon Source
## 3 Results
### Multilayered Graphene under Different Velocities of CO\({}_{2}\) Flow  
In order to study the effect of different velocities of CO\({}_{2}\) flow, a range of velocities of CO\({}_{2}\) (20, 40, 60, 80, 100, and 120 mL/min) were used at a reaction temperature of 600 \({}^{\circ}\)C with a reaction time of 30 min and 1.0 M HCl solution for sample post-processing. Figure 2 shows the yield of the multilayered graphene prepared from the Mg ribbon and Mg powder under different velocities of CO\({}_{2}\), respectively. It can be seen that both Mg ribbon and Mg powder demonstrate a similar trend: the yield increased distinctly with velocity when the velocity of CO\({}_{2}\) was below 60 mL/min and it stayed constant with the increase of velocity when the velocity was above 60 mL/min. Therefore, a velocity of 60 mL/min seems to be the optimum condition for multilayered graphene production.  
According to Equation (1), 3 g Mg can react with \(6.17\times 10^{-2}\) mol CO\({}_{2}\) (51.03 mL/min of CO\({}_{2}\) for 30 min, according to Equation (3)). Therefore, the amount of CO\({}_{2}\) is not enough to react with metal Mg when the velocity is below 40 mL/min. As the velocity of CO\({}_{2}\) increases, excess CO\({}_{2}\) can react with Mg adequately. Thus, the yield remains steady after the velocity reaches 60 mL/min.  
Moreover, given the same gas velocity of CO\({}_{2}\), the reaction of Mg powder always presents a higher yield than that of the Mg ribbon. This phenomenon can be illustrated by the interface model in a gas-solid noncatalytic reaction proposed by [PERSON] et al. (2016) According to this model, the solid pellet is visualized as consisting of a number of small particles or grains. Surrounding these grains are macropores, through which the gas has to diffuse to reach the various grains. The reaction occurs at the surface of each grain, and a product layer forms with time in the outer regions of each grain. As the time is prolonged, the product layer becomes too thick for gas to diffuse to reach the various grains in turn, so the reaction ceases. In this case, the metal Mg can be served as small particles. Surrounding the small particles of metal Mg are macropores through which gaseous CO\({}_{2}\) can diffuse to reach the small particles of metal Mg and react with Mg on the surface to form multilayered graphene. With the reaction's progress, multilayered graphene prepared on the surface of metal Mg becomes too dense for CO\({}_{2}\) to diffuse, so in turn, the reaction ceases. Compared with the Mg ribbon, Mg powder had much more macropores for CO\({}_{2}\) to diffuse and react with metal Mg because the structure of Mg  
Figure 2: The yield under different velocities of CO\({}_{2}\) prepared with an Mg ribbon and Mg powder.  
powder was more looser (as Figure 1 shows). Consequently, a higher yield was obtained from Mg powder. This agrees well with the SEM result, which implies that Mg powder has a higher specific surface area than that of Mg ribbon because of the sphere-like structure of Mg powder. Hence, it is easier for Mg powder to react with CO2 when given the same amount of metal Mg in such conditions.