Characterization of Magnetic Carbon Nanotube–Cyclodextrin Composite and Its Adsorption of Dye

β-Cyclodextrin (CD) grafted carbon nanotube (CNT) composites were prepared by the reduction of oxidized CNT with hydrazine hydrate in the presence of CD. The obtained reduced CNT-CD (RCNT-CD) was attached to iron oxide particles in preparation of magnetic RCNT-CD (M-RCNT-CD). These composites were characterized by Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TG). About 17 wt % CD was grafted onto RCNT, and about 23.5 wt % iron oxide particles were attached to the RCNT-CD. The kinetic adsorption fit the pseudo-second-order model, and the isotherm data followed the Langmuir model. The maximum adsorption capacity reached 196.5 mg/g for M-RCNT-CD, indicating that it is a good adsorbent for methylene blue. The positive free energy change (ΔG°) and negative enthalpy change (ΔH°) illustrated that the adsorption process was spontaneous and endothermic. M-RCNT-CD can be easily separated from solution in the magnetic field.