Amino-functionalized multi-walled carbon nanotubes (NH₂-MWCNTs) for the removal of methyl orange (MO) from aqueous solution were prepared for the first time using 1,6-hexanediamine by a simple one-pot process at 198 °C for 8 h. The resulting materials were characterized by different techniques, such as TEM, FTIR, XPS, Raman, elemental analysis and BET surface area measurement. Experimental results indicated that the amount of 1,6-hexanediamine bound on MWCNTs was estimated to be around 5 wt% and the materials showed an excellent adsorption capacity (q_max = 185.53 mg g⁻¹). The adsorption equilibrium could be reached within 10 min. Both Langmuir and Freundlich models showed a better fit with experimental data than the Temkin model and the adsorption kinetics could be accurately described by the pseudo-second-order model. The overall rate process was jointly controlled by intra-particle diffusion and external mass transfer. Moreover, the thermodynamic parameters indicated that the adsorption was spontaneous and exothermic. Results of this work are of great importance for environmental applications of amino-functionalized multi-walled carbon nanotubes as promising dye adsorbents in wastewater treatment.