Activated carbon/NiFe2O4 magnetic composite: A magnetic adsorbent for the adsorption of methyl orange

Activated carbon/NiFe2O4 (AC/NiFe2O4) magnetic composite was synthesized by a facile hydrothermal synthesis method. This synthetic approach involves the mixing of aqueous solution of FeCl3 and NiSO4 with AC and aqueous NaOH to yield a mixture. The mixture was subsequently sealed and heated at 453 K for 10 h. The AC/NiFe2O4 composites synthesized by the method mentioned above were characterized by X-ray diffraction (XRD), nitrogen adsorption isotherms, vibrating sample magnetometer (VSM) and Fourier transform infrared (FT-IR) spectroscopy. Methyl orange (MO) dye was selected as a model of azo dyes to investigate the adsorption property of AC/NiFe2O4 magnetic composite. The adsorption conditions including AC content, the pH and concentration of MO solution, contact time, temperature, adsorbent dosage and ionic strength were systematically investigated by batch adsorption experiments. The MO removal efficiencies could reach 93% in the first 2 min and 99% within 30 min at the temperature of 303 K. Several isotherm models were investigated and adsorption isotherm data fitted well with Langmuir isotherm model. The Langmuir isotherm model exhibited a maximum adsorption capacity qmax of 182.82 mg g−1 at 303 K. The kinetic data were well described by pseudo-second-order model. The overall adsorption process was jointly controlled by external mass transfer and intraparticle diffusion, and intraparticle diffusion was the rate-dominating step. Thermodynamic parameters including ΔGo, ΔHo and ΔSo were calculated, suggesting that the adsorption of MO onto AC/NiFe2O4 composite was spontaneous and endothermic process. Adsorption interactions of MO onto AC/NiFe2O4 composite from aqueous solutions were investigated using FT-IR spectroscopy. The remarkable adsorption capacity of MO onto AC/NiFe2O4 composite can be attributed to the hydrogen bonding interaction between MO and AC/NiFe2O4 composite. Regeneration experiment showed that AC/NiFe2O4 composite can be used as adsorbent for the removal of MO six times. The AC/NiFe2O4 composite as adsorbent for MO were easily dispersed, separated and removed in an external applied magnet field, and can be more convenient for large scale applications than filtration or centrifugation separation route.