Magnetic iron oxide nanoparticles: synthesis and surface functionalization strategies

Abstract

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

Figure 1

The representative structure of organic materials functionalized magnetic iron oxide NPs (if iron oxide NPs were always assumed as the core)

Figure 2

Scheme for the magnetic NPs functionalization procedure described in this work. Steps 1A and 1B: ligand-exchange reactions. Step 2: acylation of hydroxyl groups to prepare ATRP surface initiators. Step 3A: surface-initiated ring opening polymerization of l-lactide. Steps 3B: surface-initiated ATRP. Step 4: deprotection or additional reaction after polymerization. Step 5: graftiong of endfunctionalized PEG chains onto the nanoparticle surface using amidation chemistry. From [57]

Figure 3

Physicochemical mechanism for modifying the silane agents on the surface of iron oxide NPs

Figure 4

Illustration of the synthesis route of polystyrene coated magnetic NPs with core/shell structure. From [98]

Figure 5

The main structure of inorganic materials functionalized iron oxide NPs (if iron oxide NPs were always assumed as the core)

Figure 6

Schematic for SiO₂/MP-QD nanocomposites synthesis (left); TEM micrographs of aγ-Fe₂O₃ MPs; b SiO₂/MP; c interconnected MPs and CdSe QDs (after 8 h of SiO₂/MP-QD reaction); de SiO₂/MP-QD nanocomposites (after 48 h of SiO₂/MP-QD reaction; note the presence of both Fe₂O₃ MPs and CdSe QDs (finer crystallites denoted by arrows in panel e)); and f SiO₂/MP-QD nanocomposites formed at a lower CdSe concentration (0.5 mg/mL of cyclohexane); g High resolution TEM micrograph of the area marked by the arrow in (f), showing the presence of CdSe QDs and γ-Fe₂O₃ MPs. From [113]

Figure 7

Synthetic scheme for the preparation of the three-layer NPs (left); TEM images of colloids after each synthetic step. ab SiO₂ particles covered with silica-primed Fe₃O₄ NPs (SiO₂–Fe₃O₄). cd SiO₂ particles covered with silica-primed Fe₃O₄ NPs and heavily loaded with Au nanoparticle seeds (SiO₂–Fe₃O₄–Au seeds). e Three-layer magnetic NPs synthesized in a single-step process from particles presented in (c) and (d). Note the uniformity of the gold shell. The inset shows the three-layer magnetic NPs drawn to the wall with a magnet. From [125]

Figure 8

Illustration of the preparation of Fe₃O₄@SiO₂–Gn–PAMAM–Pd(0) inorganic–organic hybrid composites (left); HRTEM images of MRCs (Right). From [140]

Figure 9

Scheme of the synthetic route to Fe₃O₄@TiO₂ core-shell NPs. From [153]