▎ 摘　　要

Magnetic Fe3O4@graphene nanocomposite (FGN) was synthesized by co-precipitation method. The ability and mechanism of FGN to remove 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution were evaluated. Results showed that the adsorption of 2,4-D on FGN exhibited a strong pH dependence and optimal pH value was 3. Based on density functional theory, pi-electron density was enhanced when 2,4-D molecule dissociated into 2,4-D anion, which was beneficial to pi-pi interaction. The decreased 2,4-D adsorption uptake with increasing pH was mainly caused by electrostatic repulsion. The presence of NaCl (1-20 mmol/L) exerted ignorable influence on 2,4-D removal. Adsorption kinetics and isotherms could be better represented by pseudo-second kinetic and Langmuir adsorption isotherm, respectively. The maximum adsorption capacity was calculated to be 32.31 mg/g at 303.15 K according to Langmuir model. Thermodynamic parameters revealed that the adsorption was an exothermic and spontaneous process. The adsorption of FGN for 2,4-D was mainly driven by pi-pi interaction between benzene ring of 2,4-D and graphene, which was demonstrated by FTIR spectrums. Fe3O4 contributed to the removal of 2,4-D through electrostatic attraction at low pH. Moreover, FGN still remained certain adsorption capacity following four desorption/regeneration cycles. (C) 2016 Elsevier B.V. All rights reserved.