# Carbon Spheres as CO\({}_{2}\) Sorbents
## 3 Results and Discussion
### Adsorption Studies
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Sample**} & **Density** & **S\({}_{\text{SET}}\)** & **Total Pore Volume** & **CO\({}_{2}\) Adsorption at 0** & **CO\({}_{2}\) Adsorption at \\  & **(g/cm\({}^{3}\))** & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & \({}^{\circ}\)C (mmol/g)** & **25 \({}^{\circ}\)C (mmol/g)** \\ \hline RF 700 & 1.79 & 444 & 0.25 & 3.25 & 2.43 \\ RF 7/1 600 & 1.68 & 599 & 0.34 & 3.73 & 3.41 \\ RF 7/1 700 & 1.97 & 645 & 0.43 & 5.15 & 3.67 \\ RF 7/1 800 & 2.26 & 1331 & 0.74 & 5.52 & 3.96 \\ RF 9/1 600 & 1.75 & 530 & 0.29 & 3.79 & 3.20 \\ RF 9/1 700 & 1.80 & 843 & 0.46 & 4.43 & 3.74 \\ RF 9/1 800 & 1.95 & 1252 & 0.68 & 5.56 & 3.87 \\ RF EDA 600 & 1.59 & 396 & 0.24 & 2.66 & 1.94 \\ RF EDA 700 & 1.67 & 369 & 0.20 & 2.57 & 2.01 \\ RF EDA 800 & 1.72 & 341 & 0.19 & 3.01 & 2.28 \\ RF 7/1 EDA 600 & 1.62 & 439 & 0.27 & 3.50 & 2.51 \\ RF 7/1 EDA 700 & 1.74 & 1114 & 0.64 & 5.89 & 4.60 \\ RF 7/1 EDA 800 & 1.99 & 1614 & 0.93 & 6.21 & 4.02 \\ \hline \end{tabular}
\end{table} 
Table 4: Physico-chemical properties of the obtained samples. Figure 8: PSD (Pore Size Distribution) calculated from CO\({}_{2}\) adsorption at 0 \({}^{\circ}\)C for the samples modified with EDA only. In the research paper [21], doping of the carbon spheres with EDA was described. Increasing the EDA ratio (from 0.2 mL to 0.8 mL for 0.4 g of resorcinol) led to an improvement of specific surface area and CO\({}_{2}\) uptake at 25 \({}^{\circ}\)C. The work of [PERSON] et al. [34] also reported a positive effect of a higher concentration of EDA as a modificator, improving the CO\({}_{2}\) uptake. In the present paper, more detailed studies on the influence of carbonization temperature on samples modified with EDA were performed. The samples modified with EDA showed much lower surface areas and CO\({}_{2}\) adsorption than the reference sample RF 700. A higher carbonization temperature resulted in lower surface area (Table 4) and lower total pore volume, but an increase of the CO\({}_{2}\) uptake was observed. This observation can be explained by higher micropore volume, below 0.4 nm for the sample RF EDA 800 (Figure 8). At elevated temperatures, carbon spheres have a tendency to aggregate, thus the effective surface area decreased. Density measurements proved the increase of density (from 1.59 g/cm\({}^{3}\) for RF EDA 600 to 1.72 g/cm\({}^{3}\) for RF EDA 800). In contrast, an increase in the carbonization temperature increased the volume of the pores below 0.4 nm (Figure 8) and consequently the CO\({}_{2}\) adsorption capacity. Significant differences were noticed for the samples modified with potassium oxalate. In the paper [19], [PERSON] and [PERSON] applied three potassium oxalate concentrations, with a K:C ratio of 3:1, 5:1, and 7:1. The growth in surface area (460 m\({}^{2}\)/g for pure material and 2130 m\({}^{2}\)/g for the highest concentration potassium oxalate) and CO\({}_{2}\) adsorption (2.8 mmol/g for pure material and 6.6 mmol/g for the highest concentration potassium oxalate) was observed. In order to investigate the influence of the activator concentration on the physico-chemical properties of the spheres, we employed a higher concentration of potassium oxalate monohydrate (weight ratio K:C = 9:1). The specific surface area values were similar to the values for samples with a lower activator concentration. A significant difference in CO\({}_{2}\) uptake at 0 \({}^{\circ}\)C and 25 \({}^{\circ}\)C was observed for sample RF 9/1 carbonized at 800 \({}^{\circ}\)C.  
The microporosity of these samples carbonized in 700 \({}^{\circ}\)C is given in Figure 9. The sample RF 700, compared to the samples modified with potassium oxalate, had the lowest specific surface area. This was caused by a lack of energized potassium ions to interact with the carbon matrix and a lack of carbon dioxide released in the result of decomposition of potassium oxalate, creating porosity.