# Carbon Spheres as CO\({}_{2}\) Sorbents
## 3 Results and Discussion  
### Samples' Morphology  
The morphology of the carbon spheres was studied using Scanning Electron Microscopy (SEM). The SEM images of the samples carbonized in 700 \({}^{\circ}\)C are shown in Figure 1. For the material without modification (Figure 1a), small, monodisperse spheres were obtained. The average diameter of the carbon spheres was determined by SEM to be about 400 nm. For the material prepared by the addition of the activator (potassium oxalate, Figure 1b), two classes of spheres were observed: smaller spheres, about 500 nm in diameter, and larger, about 2-3 \(\upmu\)m. The large difference in the diameter of the spheres was the result of the addition of potassium oxalate. The resorcinol-formaldehyde spheres were influenced by the oxalate moieties, and thus larger spheres were formed. However, there was a fraction of the smaller spheres, where oxalate moieties were likely less present. The higher concentration of potassium oxalate (Figure 1c) resulted in higher saturation of the solution. The spheres containing more potassium oxalate were larger. Nonetheless, there was a large amount of small spheres, which did not contain oxalate moieties. Thus, a large amount of carbon material was not modified. For the material modified with EDA only (Figure 1d), the monodispersity of the spheres was kept, however larger spheres (diameter ca. 800 nm) were formed. The larger diameter and the monodispersity of the spheres are evidence that EDA was well dispersed in the whole volume, and so, all carbon spheres contained EDA. In the case of the material modified with both EDA and potassium  
Figure 1: Scanning Electron Microscopy (SEM) images of the spheres: (**a**) without modification; (**b**) with activator concentration 7/1; (**c**) with activator concentration 9/1; (**d**) with ethylene diamine (EDA) modification; (**e**) with activator concentration 7/1 and EDA modification. oxalate (Figure 1e), the influence of both modifiers can be noticed. The average diameter of the spheres was larger and the spheres were more uniform. EDA provided better dispersion of potassium oxalate in the reaction volume, thus potassium ions were present in a higher amount of the spheres. In the end, a much bigger specific surface area value was reached. The size distribution of the produced particles was evaluated from the SEM images using the ImageJ software tool and is illustrated in Figure 2a-e. The quantity of spheres taken into account was 50 for every kind of the sample. The results for the reference sample are given in Figure 2a. RF 700 exhibited the highest monodispersity among all the samples. The diameter of the spheres was about 600 nm. Figure 2: _Cont._  
The modification of carbon materials with the lower content of potassium oxalate resulted in higher variation in the spheres' size distribution. A considerable amount of produced spheres had a diameter from 300 to 1000 nm, as shown in Figure 2b. With the increase of the carbonization temperature, the formation of larger spheres (about 2000 nm) was observed. For the material carbonized at 600 \({}^{\circ}\)C, the majority of spheres were about 500 nm, whereas on the other hand for the sample carbonized at 800 \({}^{\circ}\)C, this value shifted to about 700 nm. Comparing the samples with different amounts of activator, the strong influence of the activator concentration on the spheres' size was noticed. Higher activator content in the samples resulted in the widest size distribution (Figure 2c). Moreover, the large spheres of diameter over 2000 nm were formed. The size distribution of the samples modified with EDA only is presented in Figure 2d. Compared to the samples modified with potassium oxalate, the highest monodispersity of the spheres was gained. Nonetheless, increasing the carbonization temperature caused the distribution to be broader. As can be seen in Figure 2e, the application of both the modificators limited the production of the large spheres (over 2000 nm).