## 4 Conclusions  
MWCNTs were prepared, purified, and functionalized in this study. MWCNTs are good alternative adsorbents with which to remove IV2R dye from aqueous solutions and wastewater. MWCNT nanocompounds were examined using SEM, FTIR, XRD, and BET surface analysis. Purified MWCNTs were characterized by FTIR, which showed the existence of functional groups such as N-H, O-H, COOH, C=N, and S-H stretching, thereby increasing their ion exchange properties for the selective adsorption of opposing charged molecules. Furthermore, various factors affecting IV2R dye elimination efficiency were examined by the batch process, including adsorbent dose, agitation time, pH, initial dye concentration, and temperature. The highest operation influences were found to be 0.04 g of MWCNTs, 10 mg L\({}^{-1}\) of dye, pH 4 at 30 \({}^{\circ}\)C, and 120 min of contact time. The percentage removal of the IV2R dyes increased with a rise in the contact time and MWCNT dosage, while it decreased with augmented initial dye concentrations, pH, and temperature. On the contrary, the equilibrium isotherm adsorption results were examined using numerous applied isotherms such as the Freundlich, Langmuir, Harkins-Jura, [PERSON], Henderson, [PERSON], and Tempkin models. A higher adsorption capacity (\(q_{\text{max}}\)) of 76.92 mg g\({}^{-1}\) was acquired from the Langmuir model. The best-fitting isotherm model in this study was obtained by different error function models. However, a kinetics study was conducted using the intraparticle diffusion, pseudo-first-order, and pseudo-second-order models. The regression data indicated that the sorption kinetics equation was the best via the pseudo-second-order model (R\({}^{2}\) = 0.999). Additionally, the percentage of removal of the MWCNTs from real wastewater reached 88%. Moreover, the thermodynamic parameters of the sorption process (\(\Delta\)G\({}^{\circ}\), \(\Delta\)H\({}^{\circ}\), and \(\Delta\)S\({}^{\circ}\)) were calculated. The adsorption of IV2R dye was endothermic, and was a spontaneous process, and the reaction of adsorption is a physisorption process. The efficiency of the regenerated MWCNTs showed a slight change after three cycles of reuse and regeneration.  
Conceptualization, A.E.A.; methodology, A.E.A. and K.M.A.; software, A.E.A. and K.M.A.; formal analysis, A.E.A., M.A., and A.T.M.; investigation, A.E.A.; resources, A.E.A. and K.M.A.; data curation, A.E.A., M.A. and A.T.M.; writing--original draft preparation, A.E.A., M.A., and A.T.M.; writing--review and editing, A.E.A., M.A., K.M.A., and A.T.M.; visualization, K.M.A.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**CNTs** & **Dye Adsorbed** & \(q_{e}\) **(mg g\({}^{-1}\))** & **Ref.** \\ \hline MWCNTs & Sufranine O & 43.48 & [65] \\ \hline MWCNTs & Methylene blue & 35.4 & [67] \\ \hline Oxidize MWCNTs & Bromothymol blue & 55 & [25] \\ \hline SWCNT–COOH & Basic red 46 & 45.33 & [1] \\ \hline MWCNTs & methylene blue & 64.7 & [67] \\ \hline MWNTs & Orange II & 66.12 & [68] \\ \hline SWCNT & Basic red 46 & 38.35 & [69] \\ \hline MWNTs & Reactive blue & 335.7 & [19] \\ \hline MWNTs & Alizarin red S & 161.290 & [70] \\ \hline MWCNTs & Reactive blue 4 & 502.5 & [19] \\ \hline MWNTs & Methyl orange & 52.86 & [17] \\ \hline CNTs/activated carbon fiber & Basic violet 10 & 220 & [71] \\ \hline MWCNTs/Fe\({}_{3}\)C & Direct Red 23 & 172 & [72] \\ \hline Chitosan/Fe\({}_{2}\)O\({}_{3}\)/MWCNTs & Methyl orange & 66.90 & [21] \\ \hline MWCNTs/Fe\({}_{2}\)O\({}_{3}\) & Methylene blue & 42.3 & [73] \\ \hline MWCNT & & 76.9 & Present study \\ \hline \hline \end{tabular}
\end{table}
Table 7: Summary of the elimination of several dyes from aquatic mixtures by various carbon nanotubes.  
and M.A.; supervision, K.M.A. project administration, A.E.A.; funding acquisition, K.M.A. All authors have read and agreed to the published version of the manuscript.  
The authors appreciated Taif University Researchers Supporting Project number TURSP-2020/267, Taif University, Taif, Saudi Arabia.