Recent Advances in the High‐Temperature Chemical Synthesis of Magnetic Nanoparticles

Abstract

Depending on the solvent chosen, high temperatures can be used to control metal precursor reaction and the formation of magnetic NPs. It is versatile in controlling NP size, shape, structure and composition. [ 7 ] In this chemical context, two methods are commonly used. The fi rst one relays on the rapid injection of the reagents, which are often organometallic compounds, into hot surfactant solution, inducing the simultaneous formation of many nuclei ( Figure 1 ). Alternatively, reducing agents can be quickly added to metal salt solutions at high temperature. In both cases nucleation occurs when the monomer concentration is quickly increased over the critical supersaturation level; this nucleation stage relieves the supersaturation. [ 8 ] After the nucleation event, the preformed nuclei start to grow from the remaining monomers without additional nucleation events, leading to the formation of NPs. [ 9 ] To gain control of the NP size distribution, the nucleation events should occur simultaneously for all nucleating monomers, and the NP growth condition should be kept identical in the reaction solution. In the second common synthetic procedure, reagents are mixed at low temperature and the reaction is slowly heated in a controlled manner to generate nuclei. Subsequently, NP growth occurs by the addition of reactive species [ 7 ] or by Oswalt ripening, [ 9 ] where the high surface energy of the small NPs promotes their dissolution and the subsequent redeposition of the material on the larger NPs. These bottom-up approaches have proven to be very successful in the preparation of a large family of Fe and Co-based magnetic NPs. Fe NPsMagnetic NPs based on metallic Fe have much higher magnetization values than their oxide counterparts (Fe, 218 emu g -1 ) [ 10 ] which is very attractive for biomedical applications like bioseparation, highly sensitive biosensing and MRI contrast enhancement. Although Fe NPs may be highly reactive in an aqueous environment, issues of biocompatibility, solubility, and stability can be addressed, for example, by coating the NPs with an inert inorganic layer and/or polymer. [ 11 ] Fe NPs are made by thermal decomposition and reduction of metal precursors followed by high temperature or other chemical treatments to form a robust shell of carbon, [ 12 ] oxides, [ 10,13 ] or noble metals. [ 14 ] It is well known that highly crystalline Fe NPs could be made by reduction of a dimeric iron precursor with H 2 ; however, once exposed to air, these NPs are

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…Healthcare Mater. 2017, 6,1700306 restrictions is exerted by the body, nanoparticles with narrow size distribution range near to the optimum size and shape will be drastically required to prevent their filtration from the bloodstream. On the other hand, surface properties of MNPs such as surface charge and hydrophobicity play an important role in defining their biological identity within the body.…”

“…[300] In the case of fungi-mediated biosynthesis of magnetite nanoparticles, up to our knowledge, there is only one study performed by Bharde et al [301] Within this elegant study, magnetite nanoparticles with appropriate stoichiometry were produced by challenging F. oxysporum and Verticillium sp. with an aqueous solution containing a mixture of ferricyanide [Fe(CN) 6 ] 3+ ions and ferrocyanide [Fe(CN) 6 ] 4+ ions. TEM images of the resultant magnetite nanoparticles revealed that magnetite nanoparticles of quasi-spherical shape in the 20-50 nm size range were synthesized by F. oxysporum, while verticillium sp.…”

Lithiumpyridinyl‐Driven Synthesis of High‐Purity Zero‐Valent Iron Nanoparticles and Their Use in Follow‐Up Reactions

“…Zero‐valent iron nanoparticles are relevant in regard of different aspects ranging from fundamental science to potential application. First of all, Fe(0) is well‐known for its ferromagnetic properties and in the case of spherical nanoparticles specifically for its superparamagnetism, which can be used for soft magnetic applications as well as magnetic liquids . Fe(0) is an essential constituent of prominent organometallic compounds such as iron carbonyls (e.g., Fe(CO) 5 ) .…”

“…First of all, Fe(0) is well-known for its ferromagnetic properties and in the case of spherical nanoparticles specifically for its superparamagnetism, [1] which can be used for soft magnetic applications as well as magnetic liquids. [2] Fe(0) is an essential constituent of prominent organometallic compounds such as represents a straightforward one-pot approach and is performed in the absence of any oxygen source (e.g., starting materials, solvents, stabilizers). As a result, uniform Fe(0) nanoparticles with a size of 3-5 nm and high purity were obtained.…”

Synthesis of Distinct Iron Oxide Nanomaterial Shapes Using Lyotropic Liquid Crystal Solvents

“…The most common synthetic methods for creating functional IO NPs (i.e., the co-precipitation method by Massart [ 28 ], and the solvothermal method by Sun [ 29 ]) yield quasi-spherical particles or IO cubes in the range of tens of nanometers or smaller. While there are numerous papers that describe methods for creating non-spherical IO nanostructures [ 30 ] (particularly wires [ 23 , 31 ], rods [ 32 , 33 , 34 , 35 , 36 ], cubes [ 37 , 38 , 39 ], and sheets [ 40 ]), fewer of those are used or investigated for in-depth (bio)medical research. While there is a wealth of data for T2 MRI contrast enhancement and magnetic hyperthermia use of such IO nanoshapes [ 41 ], specific cell uptake [ 42 ] in various relevant tissue or cancer cell lines as well as their intracellular behavior have remained, to a large extent, unexplored.…”