# Carbon Spheres as CO\({}_{2}\) Sorbents
## 4 Discussion  
The modificators played a double role in this reaction system: first creating more porosity and second, giving a basic chemical character to the produced material. In our previous paper [33], chemical activation of carbon spheres using a similar amount of potassium oxalate monohydrate was achieved. In the case of the materials prepared with potassium oxalate monohydrate, two activation mechanisms can be distinguished. First, potassium ions penetrate the carbon material and a high porosity material was formed [38]. The effect of a higher carbonization temperature resulted in more energetic potassium ions migrating into the nanocarbon spheres. Second, decomposition of potassium oxalate monohydrate at about 570 \({}^{\circ}\)C resulted in the release of CO\({}_{2}\), which would help remove pyrolyzed volatile products from the carbon matrix and could also prevent an aggressive pore widening process, leading to better microporosity [39; 40]. Potassium oxalate decomposes to release carbon dioxide and to form potassium carbonate. The latter decomposed above  
Figure 10: CO\({}_{2}\) adsorption values of the tested samples. Figure 9: PSD calculated from CO\({}_{2}\) adsorption at 0 \({}^{\circ}\)C for the samples carbonized at 700 \({}^{\circ}\)C.  
700 \({}^{\circ}\)C, also with the release of carbon dioxide, and then, an increase of carbonization temperature from 700 to 800 \({}^{\circ}\)C resulted in an increase in specific surface area by over 100%, from 645 to 1331 m\({}^{2}\)/g (Table 4). Nonetheless, the CO\({}_{2}\) adsorption values were only slightly enhanced (from 5.15 to 5.52 mmol/g at 0 \({}^{\circ}\)C). EDA also decomposes at elevated temperatures, with the release of ammonia, carbon dioxide, carbon monoxide, nitrogen oxides, and/or volatile amines. However, the release of the gaseous decomposition products did not result in an increase of the porosity of the material. Thus, the use of EDA alone did not change the physical properties of the material. The best results were obtained when both activators were applied. We posit that EDA reacted with potassium oxalate, forming the chelates, which improved the homogeneous distribution of potassium within the sample volume. This can be explained by the trapping of migrating potassium ions by amine groups. The ability of EDA to form chelates with metals (\"amino acid metals\") is well known. Half of EDA produced by the Dow Chemical Company [41] is used as a chelating agent, forming complexes with certain metal ions to prevent the ions from interfering with processing or to promote buffering, concentration, separation, or transport. Carbonization at high temperatures caused decomposition of both modificators and of the formed chelates, nevertheless some potassium remained in the samples and had a positive effect on the adsorption properties towards carbon dioxide, increasing surface basicity. Potassium can form carbides with carbon. According to the literature [42], there is a possibility of the formation of the following potassium carbides: KC\({}_{8}\), KC\({}_{16}\), KC\({}_{24}\), KC\({}_{32}\), KC\({}_{48}\), and KC\({}_{60}\). These carbides have graphite-like lattices in which the metal atoms are situated between the layers of carbon atoms. The metal atoms are located at the centers of the carbon hexagons. Relevance of the presence of pores below 1 nm in the matter of CO\({}_{2}\) adsorption has been widely documented [43; 44]. [PERSON] and coworkers [45] claimed that under atmospheric pressure, the contribution of the pores below 0.8 nm to the CO\({}_{2}\) adsorption was the most significant. Pore size distributions of the modified samples showed that use of chemical activator was necessary, i.e., potassium oxalate monohydrate was responsible for the creation of micropores beneath 0.4 nm. Activation with potassium led to the creation of irregularities on the surface of carbon materials [46]. [PERSON] and [PERSON] [47] investigated pore structure development in carbon materials produced from resins.