## 5 Conclusions  
Resorcinol-formaldehyde aerogels and their subsequent activated carbons (AC-RFA) were prepared. Multiwall carbon nanotubes (MWCNTs) and AC-RFA were mixed together with various ratios. Samples were characterized by various devices. Adsorption/desorption isotherms of pure CO\({}_{2}\) and CH\({}_{4}\) gases on each sample were studied. The impact of temperature on the adsorption/desorption isotherms of gases was conducted on the sample of medium composition (S50). One of key findings of this study is that the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Gas**} & \multicolumn{2}{c}{**Adsorption Capacity**} & \multirow{2}{*}{**Reference**} \\  & & **(mole/kg)** & \\ \hline AC-RFA & CO\({}_{2}\) & -2.79 & This study \\  & CH\({}_{4}\) & -2 & This study \\ Shale & CO\({}_{2}\) & 0.172 & [53] \\ AC- coconut-shells & CO\({}_{2}\) & 2.55 & [54] \\ AC- fibers & CO\({}_{2}\) & 0.7 & [55] \\  & CH\({}_{4}\) & 0.3 & [55] \\ AC-Wood pellets & CO\({}_{2}\) & 2.32 & [56] \\ AC-Waste tea & CO\({}_{2}\) & 1.98 & [57] \\ AC-Modified Waste & CO\({}_{2}\) & 2.47 & [57] \\ AC-lotus stems & CO\({}_{2}\) & 3.85 & [58] \\ AC-commercial & CO\({}_{2}\) & 6.123 & [59] \\ AC-hard coal & CH\({}_{4}\) & 7.43 & [60] \\  & CH\({}_{4}\) & 4.01 & [61] \\ AC-CCVD & CO\({}_{2}\) & 6.41 & [62] \\ AC-indigenous shells & CH\({}_{4}\) & 0.48 & [62] \\  & CO\({}_{2}\) & 1.5-3 & [63] \\ AC-xerogels & CH\({}_{4}\) & 4.5–5 & [63] \\ AC-Maxsorb II & CH\({}_{4}\) & 0.25–8.1875 & [64] \\ AC-Clay-rich shale & CH\({}_{4}\) & 3.85 & [65] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: A comparative study of recent work with some literature work. The reported values are at -1 MPa and room temperature. Figure 13: Binary amounts adsorbed (**a,c**) and selectivity (**b,d**) for an equimolar gas mixture of CO\({}_{2}\) and CH\({}_{4}\) onto the sample S50 predicted with the (**a,b**) PP and (**c,d**) PN behaviors. The amounts adsorbed of CO\({}_{2}\) and CH\({}_{4}\) are presented by solid and dashed lines, respectively. carbonaceous adsorbent structure uniformity and its order have a significant influence on pore structure, adsorption capacity and adsorption selectivity towards gases. Moreover, the highest adsorption capacity for either CO\({}_{2}\) or CH\({}_{4}\) gases was for the sample that did not contain any MWCNTs; whereas adding AC-RFA to MWCNTs enhances their adsorption capacity. Furthermore, it can be deduced that the adsorption capacity of MWCNTs towards gases is relatively very low compared to AC-RFA. The pure-component dual site Langmuir (DSL) isotherm model was applied to correlate the adsorption data onto S50 over the entire scale of pressure at various temperatures. Moreover, the extended DSL model was utilized for predicting the adsorption equilibrium of the binary gas mixture of CO\({}_{2}\) and CH\({}_{4}\) with perfect-positive (PP) and perfect-negative (PN) behaviors at various temperatures. The selectivity of adsorbing CO\({}_{2}\) from CO\({}_{2}\)/CH\({}_{4}\) gas mixtures was also investigated. This study also indicated some key findings, such as the point that the adsorption of gases can follow either of the PP or PN behaviors; while the adsorption capacities are not significantly affected by the followed adsorption behavior (i.e., PP or PN behavior). Nonetheless, the adsorption selectivity is affected significantly, if the adsorption trend follows either of the PP or PN behaviors. In the future, it is anticipated that further investigations will be carried out to improve the selectivity and adsorption capacity as well by studying different forms of carbon-carbon hybrid nanostructures. Different carbons such as SWCNTs, graphene oxides, reduced graphene oxides, graphite, etc., can be studied to evaluate their hybrid nanostructures. Furthermore, the interactions between these different carbon nanostructures shall be examined to track their mechanisms and potential applications for gas adsorption or otherwise in detail.