Topics in Current Chemistry (2020) 378:40
1 3
This preferential binding was recently used by Brewster et al. [73] to present a new
way to control the particle size and crystal phase. They varied the carbon chain
length in the iron carboxylate, which was used as the precursor, and showcased the
effect of two different ligands, amine and carboxylic acid, which were added to the
reaction [73]. They demonstrated that the size of the particles decreased as the carboxylate chain length increased in the presence of amine ligands, while no definite
trend was observed when varying the carboxylate free ligands.
The hydrothermal/solvothermal method has also been used to synthesize other
ferrites [74]. Kim et al. [75] recently demonstrated a gram scale yield of magnetite nanoclusters by modifying the procedure and utilizing trisodium dihydrate, but,
to the best of our knowledge, this is the only report for large scale synthesis using
this method. To further exploit the particles thus formed for biological applications,
surface coating becomes necessary, as will be discussed in detail in the subsequent
section. Polymers such as polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) and
polyethanolimine (PEI), have been shown to improve the magnetic properties when
used in the synthesis of monodispersed clusters [76]. Recently, Köçkar et al. [77]
explained a way to get in-situ capping of IONPs with tartaric acid/ascorbic acid/
mixture of two, which led to the synthesis of uniform, un-agglomerated, biocompatible particles of less than 8 nm with good saturation magnetization. The hydrothermal/solvothermal method is, therefore, an ideal method for the synthesis of iron
oxide nanoparticles, mainly nanoclusters. However, the main disadvantage of this
method is that, due to the lack of stirring inside the autoclave, monodispersity, as
well as scalability, can sometimes be hindered.
2.4 Polyol Method
This method is an iteration of the solvothermal method, with polyols being used
as solvents to synthesize nanoparticles by dissolving the precursor, solubilizing
in the diol at high temperatures, and eventually leading to the formation of metal
nuclei and particles. Following previous works pertaining to synthesis of metallic
powders [78–84], Caruntu et al. described this method to synthesize nanocrystalline metal oxide nanoparticles by synthesizing magnetite nanoparticles [85]. They
explained the mechanism stating that reduction starts from the liquid state rather
than the solid, and the nanoparticles are formed in two steps: hydroxides are formed
first and then metal centers are chelated. Heterogeneous nucleation performs better than homogeneous nucleation as it has been studied to provide a better separation between nucleation and growth, thus giving better control over the size, shape
and crystallinity [78]. Polyols play multiple roles, acting as reducing agent, stabilizer and solvent [86], modulating the process to yield large and small clusters [87],
nanoparticles [88] or single-core/multicore nanoparticles [89]. Different polyols
have been exploited for the synthesis of iron oxide nanoparticles, such as diethylene glycol, giving 3 nm particles [90], or triethylene glycol, giving 10 nm particles [91]. However, Cai et al. [92] reported that only triethylene glycol gives nonaggregated nanoparticles. To our knowledge, there are no reports on the use of tetra
or penta ethylene glycol, which could have ameliorated the agglomeration problem
56
Reprinted from the journal
1 3
This preferential binding was recently used by Brewster et al. [73] to present a new
way to control the particle size and crystal phase. They varied the carbon chain
length in the iron carboxylate, which was used as the precursor, and showcased the
effect of two different ligands, amine and carboxylic acid, which were added to the
reaction [73]. They demonstrated that the size of the particles decreased as the carboxylate chain length increased in the presence of amine ligands, while no definite
trend was observed when varying the carboxylate free ligands.
The hydrothermal/solvothermal method has also been used to synthesize other
ferrites [74]. Kim et al. [75] recently demonstrated a gram scale yield of magnetite nanoclusters by modifying the procedure and utilizing trisodium dihydrate, but,
to the best of our knowledge, this is the only report for large scale synthesis using
this method. To further exploit the particles thus formed for biological applications,
surface coating becomes necessary, as will be discussed in detail in the subsequent
section. Polymers such as polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) and
polyethanolimine (PEI), have been shown to improve the magnetic properties when
used in the synthesis of monodispersed clusters [76]. Recently, Köçkar et al. [77]
explained a way to get in-situ capping of IONPs with tartaric acid/ascorbic acid/
mixture of two, which led to the synthesis of uniform, un-agglomerated, biocompatible particles of less than 8 nm with good saturation magnetization. The hydrothermal/solvothermal method is, therefore, an ideal method for the synthesis of iron
oxide nanoparticles, mainly nanoclusters. However, the main disadvantage of this
method is that, due to the lack of stirring inside the autoclave, monodispersity, as
well as scalability, can sometimes be hindered.
2.4 Polyol Method
This method is an iteration of the solvothermal method, with polyols being used
as solvents to synthesize nanoparticles by dissolving the precursor, solubilizing
in the diol at high temperatures, and eventually leading to the formation of metal
nuclei and particles. Following previous works pertaining to synthesis of metallic
powders [78–84], Caruntu et al. described this method to synthesize nanocrystalline metal oxide nanoparticles by synthesizing magnetite nanoparticles [85]. They
explained the mechanism stating that reduction starts from the liquid state rather
than the solid, and the nanoparticles are formed in two steps: hydroxides are formed
first and then metal centers are chelated. Heterogeneous nucleation performs better than homogeneous nucleation as it has been studied to provide a better separation between nucleation and growth, thus giving better control over the size, shape
and crystallinity [78]. Polyols play multiple roles, acting as reducing agent, stabilizer and solvent [86], modulating the process to yield large and small clusters [87],
nanoparticles [88] or single-core/multicore nanoparticles [89]. Different polyols
have been exploited for the synthesis of iron oxide nanoparticles, such as diethylene glycol, giving 3 nm particles [90], or triethylene glycol, giving 10 nm particles [91]. However, Cai et al. [92] reported that only triethylene glycol gives nonaggregated nanoparticles. To our knowledge, there are no reports on the use of tetra
or penta ethylene glycol, which could have ameliorated the agglomeration problem
56
Reprinted from the journal