Synthesis of carboxymethyl-β-cyclodextrin conjugated magnetic nano-adsorbent for removal of methylene blue

A novel nano-adsorbent is fabricated by the surface modification of Fe3O4 nanoparticles (MNP) with carboxymethyl-β-cyclodextrin (CM-β-CD) and the feasibility of employing these nano-adsorbents for removal of methylene blue (MB) from aqueous solutions are investigated. CMCD–MNP(C) and CMCD–MNP(P) are fabricated by grafting CM-β-CD on the surface of magnetite by covalent bonding via carbodiimide method (two-steps method) and by co-precipitation method (one-step method), respectively. Analyses by TEM and VSM reveal that both CMCD–MNP(C) and CMCD–MNP(P) are superparamagnetic with mean diameter of about 12 nm. The CM-β-CD grafting is confirmed by FTIR, TGA and zeta potential measurement. The TGA results show that CM-β-CD grafted onto CMCD–MNP(C) and CMCD–MNP(P) is 4.7 and 12 wt%, respectively. The adsorption of MB on both adsorbents is found to be dependant on pH, and initial MB concentration. Almost constant MB removal is found in the pH range of 4–10 and more MB is adsorbed at pH ∼ 12. The kinetic data for MB adsorption is found to follow a pseudo-second-order kinetic model. The equilibrium data in aqueous solutions are well represented by the Langmuir isotherm model. The adsorption capacities of methylene blue onto CMCD–MNP(P) and CMCD–MNP(C) are found to be 277.8 and 140.8 mg/g, respectively and the negative value of free energy changes indicates the spontaneous nature of adsorption. The adsorbed MB can be desorbed by using methanol solution containing acetic acid. In addition, adsorption mechanism of MB is studied through FTIR analysis.