Preparation of Fe3O4@Au core–shell magnetic nanoparticles and their potential applications in heavy metal sensing

Abstract This study aimed to develop a synthesis method for Fe 3 O 4 @Au core–shell magnetic nanoparticles using coprecipitation method and sonochemical technique to exploit their potential applications in heavy metal detection. The process began with the formation of a magnetite (Fe 3 O 4 ) core, followed by coating with gold (Au) through the reduction of gold ions from HAuCl 4 using ultrasonic waves. These waves facilitate the integration of the magnetite core with the gold layer, hence resulting in nanoparticles having uniform size and distribution. The sonochemical method was expected to enhance the synthesis efficiency and provide better control over particle size and morphology. Characterization techniques employed include X-Ray Diffraction (XRD) for crystal structure identification, Vibrating Sample Magnetometer (VSM) for magnetic properties, Particle Size Analyzer (PSA) for size distribution, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) for morphology and elemental composition, and UV–vis DRS spectroscopy for confirming the gold layer presence. The results showed that the crystal structure of the nanomaterials had a cubic inverse spinel with Fe 3 O 4 and FeO(OH) (goethite) phases. The Fe 3 O 4 @Au nanoparticles had a remanent magnetization of 5.38 emu g −1 , saturation magnetization of 37.94 emu g −1 , and coercivity of 81.55 Oe. PSA results revealed an average nanoparticle size of 11.64 nm with a PDI of 0.35, whereas SEM/EDS confirmed the presence of Fe, Au, and O, and UV–vis DRS showed a maximum reflectance peak around 511–537 nm. The sensor characterization for heavy metal detection has demonstrated an effective performance, with detection ranges for Ag and Zn being 16–18 kΩ and 260–300 kΩ, respectively. The successful synthesis of Fe 3 O 4 @Au nanoparticles thus has been confirmed, highlighting their potential application in heavy metal detection.