## 3 Results and Discussion  
### Characterization of AC@SCF Activated Carbon  
Nitrogen sorption measurements (Figure 1a) indicated clearly that the produced AC@SCF material was microporous (D\({}_{\text{micropore}}\leq\) 2 nm). Porosimetry hysteresis loop exhibited a sharp knee in the low-pressure range (i.e., P/P\({}_{0}\) \(<\) 0.01) and an insignificant increase of the adsorbed nitrogen amount in the pressure range P/P\({}_{0}\) \(>\) 0.1, which is characteristic of microporous materials. Interpretation of sorption data by both CPSM and DFT models provided pore volume distributions, which exhibited peaks at pore diameters D\({}_{\text{micro}}\leq\) 2 nm. As can be seen from Figure 1b and Table 1, such peaks, according to the DFT model, were observed at 0.67, 1.2, and 2 nm, while, according to the CPSM model (Figure 1c, Table 2), such peaks were observed at 1.28 and 1.6 nm. Both models supported the evidence that AC@SCF was a highly microporous material. Moreover, CPSM model provided a too-low peak at 27 nm (Figure 1d), which corresponded to the insignificant increase of the adsorbed nitrogen at 0.97 \(<\) P/P\({}_{0}\) \(<\) 0.997. The micropore volume percentage was calculated by both the CPSM model [36] and the Dubinin-Raduskevitch (D-R) method [42]. The last one is also depicted in Figure 1e. As reported in Table 2, according to the CPSM model, the micropore volume was 84.5%. This evidence was supported by the D-R calculations, which estimated a micropore volume of 86.6% (Table 1). Furthermore, the CPSM model predicted 8.9% of the pore volume in the pore diameter range from 2 to 3 nm and 6.6% of the pore volume in the pore diameter range from 3 to 100 nm. According to Table 2, the total pore volume of the AC@SCF material was 0.748 cm\({}^{3}\)/g. The curvature effect on specific surface area (SSA) calculations is significant for such microporous materials. The higher the micropore volume percentage, the higher the deviation of the Brunauer-Emmett-Teller (BET) model estimations for the SSA [39] from the real value. More realistic predictions for the SSA of the microporous materials are provided by the Langmuir model (monolayer adsorption) [40]. A commonly used criterion for the accuracy of the estimations of the BET and Langmuir model is the \(C\) constant which should be positive and equal or greater to the unity (1). But for microporous material cases, the C\({}_{\text{BET}}\) is negative, while the C\({}_{\text{Langmuir}}\) (C\({}_{\text{Lang. }}\)) is positive. As shown in Table 1, for the AC@SCF carbon, the SSA according to the BET method was 1372 m\({}^{2}\)/g with a C\({}_{\text{BET}}\) value of -93 (P/P\({}_{0}\) range was from 0.05 to 0.25), while the SSA according to the Langmuir approach was 1875 m\({}^{2}\)/g with a C\({}_{\text{Lang. }}\) value of 98. According to the CPSM model [33; 34; 35], the SSA was 1870 m\({}^{2}\)/g. As shown in Table 2, the mean pore diameter calculated from the pore number distribution (D\({}^{\text{CPSM}}\)\({}_{\text{Nmean}}\)) was 1.47 nm and the mean pore diameter calculated from the pore volume distribution (D\({}^{\text{CPSM}}\)\({}_{\text{Vmean}}\)) was 3.71 nm [33; 34]. Finally, the structure complexity and the resistance to diffusion through the pore channels were described with the tortuosity factor which, according to the CPSM model, was 4.65 [37]. This is in good agreement with the values reported in the literature for Filtrasorb 400 activated carbon derived from biomass [43], which ranged between 3 and 4.6. FT-IR spectra of the fresh coffee, the spent coffee, and activated carbon which was derived from the pyrolysis and chemical activation of the spent coffee are presented in Figure 2a. The spectra of fresh coffee and spent coffee were very similar, showing several characteristic vibration bands of organic groups and oxygen-containing carbon groups.