Fe3O4 Nanoparticles: Structures, Synthesis, Magnetic Properties, Surface Functionalization, and Emerging Applications

Abstract

Magnetite (Fe₃O₄) nanoparticles (NPs) are attractive nanomaterials in the field of material science, chemistry, and physics because of their valuable properties, such as soft ferromagnetism, half-metallicity, and biocompatibility. Various structures of Fe₃O₄ NPs with different sizes, geometries, and nanoarchitectures have been synthesized, and the related properties have been studied with targets in multiple fields of applications, including biomedical devices, electronic devices, environmental solutions, and energy applications. Tailoring the sizes, geometries, magnetic properties, and functionalities is an important task that determines the performance of Fe₃O₄ NPs in many applications. Therefore, this review focuses on the crucial aspects of Fe₃O₄ NPs, including structures, synthesis, magnetic properties, and strategies for functionalization, which jointly determine the application performance of various Fe₃O₄ NP-based systems. We first summarize the recent advances in the synthesis of magnetite NPs with different sizes, morphologies, and magnetic properties. We also highlight the importance of synthetic factors in controlling the structures and properties of NPs, such as the uniformity of sizes, morphology, surfaces, and magnetic properties. Moreover, emerging applications using Fe₃O₄ NPs and their functionalized nanostructures are also highlighted with a focus on applications in biomedical technologies, biosensing, environmental remedies for water treatment, and energy storage and conversion devices.

Keywords: Fe3O4 nanoparticles; biomedical applications; biosensing; core-shell structures; energy storage; environmental applications; magnetic properties; nanocomposites; surface functionalization.

Figure 1.

Numbers of articles with the keyword “Fe₃O₄” published in the last 20 years. Data originated from the Web of Science. (Data from 2021 were collected until September 2021).

Figure 2.

Fe₃O₄ NPs with various nanostructures and sizes used in emerging biomedical, biosensing, environmental, and energy applications.

Figure 3.

(a) Magnetization versus applied field (M–H) curves for superparamagnetic (SPM) (green color) and ferrimagnetic (FM) (orange) Fe₃O₄ nanoparticles and (b) relations between size, coercivity, and magnetic behavior.

Figure 4.

(a) Schematic synthesis of Fe₃O₄ NPs with sizes of 7, 8, 9, and 10 nm. Selected TEM images of Fe₃O₄ NPs with sizes of (b) 7 ± 0.5 nm and (c) 10 ± 0.8 nm. Scale bar 20 nm. Reproduced with permission from ref. [57]. Copyright 2009 American Chemical Society. (d) TEM image of spherical Fe₃O₄ NPs with a size of 200 nm. Reproduced with permission from ref. [48]. Copyright 2005 John Wiley and Sons.

Figure 5.

(a) Schematics showing the synthesis of Fe₃O₄ nanocubes with edge lengths in the 9–80 nm range and (b) the growth mechanism of Fe₃O₄ nanocubes. Reproduced with permission from ref. [74]. Copyright 2019 American Chemical Society.

Figure 6.

(a,b) TEM and HR-TEM images of Fe₃O₄ nanorods. Reproduced with permission from ref. [79]. Copyright 2012 American Chemical Society. (c,d) TEM and HR-TEM images of porous hollow NPs. Reproduced with permission from ref. [87]. Copyright 2009 American Chemical Society. (e) TEM image of 2D hexagonal nanoplates. Reproduced with permission from ref. [85]. Copyright 2010 American Chemical Society. (f,g) TEM images of Fe₃O₄ tripods and tetrapods. Reproduced with permission from ref. [86]. Copyright 2009 Elsevier.

Figure 7.

Schematic illustration of the proposed growth model for MNCs. Reproduced with permission from ref. [76]. Copyright 2017 American Chemical Society.

Figure 8.

(a) TEM image of 22 nm nanocubes encapsulating PEG-phospholipid. (b) Image of colloidal iron oxide nanocubes. In vivo MR images of the tumor site: (c) without colloid injection and (d) after 1 h (intravenous injection). MR contrast effect of ferrimagnetic iron oxide nanocubes with different sizes: (e) T₂-weighted MR images obtained with various concentrations of iron in a 3 T field and (f) their color-coded presentation. Reproduced with permission from ref. [106]. Copyright 2012 American Chemical Society.

Figure 9.

TEM images of colloidal nanoclusters constructed from Fe₃O₄ nanocube-coated amphiphilic copolymer poly(styrene-comaleic anhydride) to form (a) monomer clusters (1 nanocube), (b) dimers and trimers (2–3 nanocubes), and (c) centrosymmetric clusters (more than 4 nanocubes). (d) Schematic illustration of the preparation of soft colloidal nanoclusters. (e) SAR values for different soft colloidal nanoclusters. Reproduced with permission from ref. [117]. Copyright 2017 American Chemical Society.

Figure 10.

(a) Synthetic scheme for GOD-encapsulated hollow iron oxide nanoparticles and (b) multifunctional therapeutic strategies for starvation–chemodynamic–hyperthermia using GOD-encapsulated hollow IONPs. Reproduced with permission from ref. [89]. Copyright 2020 American Chemical Society.

Figure 11.

(a) Magnetic signal of streptavidin-conjugated Fe₃O₄@SiO₂@PAA NPs bound to a biotinylated surface. (b) Schematic illustration of the interaction between magnetic NPs and the surface for protein detection in the EXIRM analysis. (c) EXIRM data for Protein A arising from an exchange between IgG1 and IgG2 subclasses. Reproduced with permission from ref. [43]. Copyright 2018 American Chemical Society.

Figure 12.

(a) Schematic illustration of the contact area in the biosensing of nanocubic and nanospherical Fe₃O₄. FIRMS data showing the (b) magnetization profiles versus applied force of nanocubes and nanospheres with similar volumes and (c) number of retained nanoparticles on the sensor at 1 pN. Reproduced with permission from ref. [42]. Copyright 2017 American Chemical Society.