## 4 Results and Discussion  
Figure 3 illustrates the Raman spectra of MWCNT/AC-RFA mixed samples with variable compositions. These samples (with MWCNT:AC-RFA weight ratios of 100:0, 60:40, 50:50, 40:60 and 0:100) were labeled as S100, S60, S50, S40, and S0, respectively. The spectra of carbon structures contain two main bands: the G-peak (at 1576 cm\({}^{-1}\)) and D-peak (at 1314 cm\({}^{-1}\)). The G-peak is attributed to the stretching mode of a well-ordered graphitic matrix, whereas the D-peak is assigned to the stretching mode of a defected structure or lattice in the graphite matrix (e.g., vacancies or substitutional heteroatoms or chemically attached heteroatoms) [37]. The quotient of the D-peak (\(I_{D}\)) to the G-peak (\(I_{G}\)) intensities in Raman spectra is a useful parameter to assess the structural ordering/disordering of carbons, comprising carbon nanostyles. A high \(I_{D}/I_{G}\) indicates to the existence of disorders within the carbon matrix, whereas a low value of \(I_{D}/I_{G}\) refers to a degree of crystalline perfection and less structure defects. The trend in Figure 4 shows that by increasing the ratio of AC-RFA into the sample, the \(I_{D}/I_{G}\) ratio value increases. The increment relates to increasing disorder and defects of carbon materials. The peak at 2623 cm\({}^{-1}\) (G\({}^{\prime\prime}\)-peak) for MWCNTs in Figure 3 refers to an overtone of the D-peak [38]. In further observation, it was seen that peak at 856 cm\({}^{-1}\) appears for S100 and disappears for S0. Figure 4: Effect of MWCNT/AC-RFA mixed sample compositions on the \(I_{\rm D}/I_{\rm G}\) intensity ratios. Figure 3: Raman spectra of different MWCNT/AC-RFA mixed sample compositions; namely S100, S60, S50, S40 and S0. Figure 5a-e shows NanoSEM photomicrographs of S100, S60, S50, S40 and S0 samples, respectively. The difference in the morphology of these samples is observed clearly as a reflection of increasing content of carbon nanospheres among the carbon nanotubes. Figure 6a-e shows TEM images of S100, S60, S50, S40 and S0 samples, respectively. The observations from these images support those deduced from NanoSEM photomicrographs. The elemental analyses of these samples were carried out using CHNS/O and XPS techniques. The elemental analyses, either from EDX or XPS, indicate that as the oxygen percentage is higher, the adsorption capacity increases as listed in Table S1 (Supplementary Materials). Figure 5: NanoSEM photomicrographs of different MWCNT/ AC-RFA mixed sample compositions; namely (**a**) S100, (**b**) S60, (**c**) S50, (**d**) S40 and (**e**) S0. The nitrogen adsorption/desorption isotherms at \(-\)196 \({}^{\circ}\)C on S100, S60, S50, S40, and S0 are exposed in Figure 7. The isotherms of N\({}_{2}\) gas adsorption/desorption at \(-\)196 \({}^{\circ}\)C on pure MWCNTs (i.e., the sample of S100) are classified as a type-II adsorption isotherm as defined by IUPAC. This type is often encountered in adsorption by norporous substances or in substances with macroproes or unlocked cavities [39]. Furthermore, it is noticed that almost no hysteresis exists for the sample S100, whereas it appears noticeably in the samples S60, S50, S40 and S0. The nitrogen adsorption capacities onto the samples S60, S50, S40 and S0 samples are significantly higher than that onto the sample S100. This might be because the adsorption on mesoporous AC-RFA that is present in the mixed samples ensues through multilayer adsorption pursued by capillary condensation, resulting in type-IV isotherm [40,41]. Generally, hysteresis is attributed to a thermodynamic effect, a network effect (or a combination of these two effects) and capillary condensation as well [42]. It was observed that the hysteresis on pure MWCNTs is almost zero, while the hysteresis on AC-RFA is noticeable. Moreover, the porosity of AC-RFA is higher than that of MWCNTs.