Synthesis and Characterization of Fe3O4 Core Nanoparticles Coated with TiO2 and ZnO

The room temperature synthesis of the core-shell-shell (CSS) nanoparticles was demonstrated to be green, low-cost, and reproducible. The magnetic core of Fe3O4 nanoparticles was coated with TiO2 and ZnO in two steps. The obtained CSS nanoparticles were extensively characterized by XPS, TEM, XRD, DRS-UV–vis, N2 Physisorption, Electromagnetic, and Raman spectroscopy. XPS analysis revealed that the magnetic core was successfully functionalized with the citric acid. The ratio between the ferric cations (Fe3+) and ferrous (Fe2+) is typically reported to be around two due to the presence of FeO and Fe2O3 to balance the charge in the structure. Nevertheless, XPS results demonstrated that the ratio resulted in higher stability than that of the crystal nominal structure, suggesting that the surface of the CSS is slightly enriched with Fe3+ cations. TEM results indicated an average core diameter of approximately 9±1 nm for Fe3O4 (M-US); the first shell exhibited an average thickness of 3±1 nm, while the ZnO second shell thickness resulted in around 2±1 nm. X-ray diffraction analysis identified inverse spinel, hematite, anatase, and zincite phases in M-US, MT, and MTZ, respectively. Notably, the MTZ sample also contained hematite in addition to inverse spinel. Diffuse Reflectance UV-Vis Spectroscopy results demonstrated a reduction in the band gap as the shell coverage varied. N2 adsorption-desorption isotherms indicated an increase in the surface area as the core nanoparticles were coated with the subsequent shells. Additionally, the coated samples presented a mesoporous structure with a maximum surface area of 110 m2g−1 for the MT material. Raman spectroscopy confirmed the presence of vibrational modes related to TiO2 and ZnO. The core-shell-shell nanoparticles presented suitable electronic properties to potentially be applied in the photodegradation of harmful compounds and azo dyes.