In this study, the adsorption of fluoride ion (F-) from synthetic wastewater was performed using activated carbon/Fe3O4 nanocomposite in a batch system. To prepare activated carbon (AC), oak shell was used. Also, several analyses such as BET, SEM, EDX, FTIR, XRD, VSM and DLS analyzes were used to study the structure and morphology of the AC/Fe3O4 nanocomposite. BET analysis indicated that the specific surface area of Fe3O4 and AC/Fe3O4 were 65.44 and 226.78 m(2)/g, respectively, which shows the surface area of the AC/Fe3O4 composite was significantly increased compared to Fe3O4. Also, the particle size of the AC/Fe3O4 composite was obtained 75 nm by the DLS analysis. The sorption tests indicated that the highest sorption efficiency of fluoride ion using the Fe3O4/AC nanocomposite was obtained 97.4%. Moreover, the experimental results were well fitted with the Freundlich model. The maximum monolayer uptake capacity using the AC/Fe3O4 was obtained as 454.54 mg/g and showed a remarkable adsorption capacity, whichever achieved for fluoride ion sorption. Also, zero-point charge of pH (pHzpc) was obtained 5. Furthermore, the kinetic data were described by the quasi-second-order model. Besides, the thermodynamic parameters showed that the uptake of fluoride ion with the AC/Fe3O4 nanocomposite was spontaneous, practical, and endothermic. The outcomes suggest that AC/Fe3O4 nanocomposite can be effectively applied for the Fion removal from synthetic wastewater. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.