One-step synthesis of magnetic iron–aluminum oxide/graphene oxide nanoparticles as a selective adsorbent for fluoride removal from aqueous solution

Abstract

A novel magnetic adsorbent consisting of iron–aluminum oxide nanoparticles anchored on graphene oxide (IAO/GO) was prepared through a simple one-step co-precipitation method for fluoride removal from aqueous solution. Through this one-step method, this study simplified the operation processes to realize the magnetic composite of a binary iron–aluminum mixed oxide and graphene oxide (GO). By combining the advantages of GO and IAO, IAO/GO exhibits high adsorption capacity, good acid–alkali stability, super paramagnetism and good selectivity for fluoride. With magnetic properties, the adsorbent could easily be collected from aqueous solution using an external magnetic field. The physicochemical properties of IAO/GO were characterized through N₂ adsorption/desorption, XRD, TEM, XPS, FT-IR, and AGM. Several main factors, such as dosage, initial solution pH, contact time, initial fluoride concentration, and co-existing anions, were investigated. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. Fluoride sorption onto the adsorbents fitted well with the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 64.72 mg g⁻¹ for IAO/GO. Effective fluoride removal occurred in a wide pH range from 3 to 9. IAO/GO showed good selectivity for fluoride when anions existed except for HPO₄²⁻. According to the sorption studies, electrostatic attraction, anion exchange, and inner-sphere complexation were the most likely mechanisms for fluoride sorption. Overall, based on the above-mentioned merits, the IAO/GO prepared in this study could be applied widely for fluoride removal in natural water environments.