## 3 Results and Discussion  
### Textural and Chemical Characterization of the Adsorbents  
The adsorption-desorption isotherms of N\({}_{2}\) were acquired at \(-\)196 \({}^{\circ}\)C to shed light on the effect of surface modifications on porous features of the adsorbents. Table 1 shows the surface textural properties of the adsorbents. The values of S\({}_{\mathrm{BET}}\) for ACF, aACF and nACF were 966, 1565, and 797 m\({}^{2}\)/g, respectively. The highest V\({}_{\mathrm{t}}\) and V\({}_{\mathrm{mi}}\) occurred for the aACF sample, reaching 0.7357 and 0.5028 cm\({}^{3}\)/g. Specifically, ACF modified with KOH boosted the appearance of mesopores and micropores. The values of V\({}_{\mathrm{ultra}}\) are also listed in Table 1, which follow the order aACF (0.2020 cm\({}^{3}\)/g) \(>\) ACF (0.1456 cm\({}^{3}\)/g) \(>\) nACF (0.0923 cm\({}^{3}\)/g). The KOH chemical activation of ACF gave rise to the formation of a pore skeleton, the development of porosity, and the intercalation of metallic potassium into the carbon matrix. At the activation temperature, the lattices of the carbon matrix expanded due to the action of very active and mobile metallic potassium, to give rise to a large amount of micropores [27; 28]. The decrease in S\({}_{\text{BET}}\), V\({}_{\text{t}}\) and V\({}_{\text{mi}}\) of ACF after TPEA modification could be attributed to the fact that the micropores were totally or partially blinded by N-functionalities [11]. The TPEA has a bulk and long-chain structure. Thus, the graft of TPEA on ACFs could hinder the gas molecules from getting access to the pores or depositing on the carbon surface. Moreover, if the TPEA was attached inside the pores of the ACFs, the pore would be filled with TPEA molecules and the available adsorption surface or volume would be reduced. Even though the surface area and pore volume of aACF was increased compared with the as-received ACF, the ratios of S\({}_{\text{mi}}\)/S\({}_{\text{BET}}\), V\({}_{\text{mi}}\)/V\({}_{\text{t}}\), and V\({}_{\text{ultra}}\)/V\({}_{\text{t}}\) for aACF and nACF were less than those of ACF. On the other hand, the V\({}_{\text{me}}\) for aACF and nACF raised to 2 and 1.2 times of that of ACF, respectively. It is believed that TPEA modification would block half of the macropores and close one fourth of the micropores, based on the data shown in Table 1. Several investigations have reported that KOH activation mainly generates micropores [10]; the results in this study revealed that KOH activation not only created new pores, but also widened the existing ones such that the increase of pore volume covered all pore size ranges. Figure 1 illustrates the pore size distributions (PSD) of the ACFs samples in the micropore and mesopore ranges. The previous discussion is strongly supported by Figure 1. The insets (a) and (b) of Figure 1 clearly present that, compared with ACF, the peaks of the PSD for aACF have shifted to the right, and there is a new peak at about 0.5 nm. Although nACF also has a new peak at about 0.5 nm, all peaks on its PSD are weakened, especially in the pores smaller than 0.7 nm. Figure 2 shows the FESEM images of the adsorbents. The width of a filament of ACF was micro-scaled and the well-defined striations parallel to the fibrous axis were filled on the surface of the ACF (Figure 2a). The reaction with KOH made the longitudinal striations and corroded grooving more significant, and the surface of the filament was clean (Figure 2b). The redox reactions between various