**3. Influence of Fe2+ onto magnetite properties**

The stoechiometric factor of Fe2+ and Fe3+ is important for the magnetic properties of the obtained particles (coercivity, crystallinity, sorbtion capacity, etc.) (Gorski et al., 2010). The Fe2+ chemical species direct the magnetite particles synthesis kinetics and their composition (Tronc et al., 1992). The Fe2+/Fe3+ molar ratio is highly important if one focusses on obtaining magnetite particles with specific properties. Thus, a Fe2+/Fe3+<0.l molar ratio is too small to achieve a stable solution. In this context, if the content of chemical species of Fe2+ is low, goethite (α-FeO(OH)) is obtained as the only stable product. The use of the Fe2+/Fe3+>0.1 molar ratio is favorable for obtaining magnetite instead of goethite.

The influence of the Fe2+/Fe3+ molar ratio on the characteristics of magnetite particles obtained by co-precipitation of Fe2+ and Fe3+ (composition, size, morphology and magnetic properties) was studied by Jolivet (Jolivet et al., 1992). Chemical species in different proportions were precipitated with ammonia solution to pH~11. The analysis of the products obtained with different Fe2+/Fe3+ molar ratios, in the range 0.10-0.50, concluded that for values lower than 0.30 two different phases coexist:

(a) the first phase contains particles of 4 nm in diameter, with oxyhydroxy (FeO(OH)) surface functional groups and low Fe2+ content, reflected by the ratio Fe2+/Fe3+~0.07;

(b) the second phase is characterized by increased content of Fe2+ (Fe2+/Fe3+~0.33 molar ratio), the final product is magnetite with increased particle sizes. It was noticed that the share of this phase increases with increasing the Fe2+/Fe3+ molar ratio. Thus, for values greater than 0.35, the product is found only in the second phase.

In conclusion, for a 0.5 Fe2+/Fe3+ molar ratio homogenous magnetite particles of uniform size and composition are more likely to be obtained. The order of addition of ionic species (Fe2+ and Fe3+) in co-precipitation reaction does not influence the final characteristics (size, composition) of the obtained particles.

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 155

steric, refers to the inhibition of particles aggregation by an entropic force, which appears when the particles are closed to each other. As surfactants monomers, homopolymers, block copolymers and polymers with terminal functional groups can be successfully used. After the coating process, these particles are re-suspended in proper solvents and form

**(nm)** 

8-50

N-oleoylsarcosine 8.1-20.7 Xu et al., 2004

193 (DLS) 11 (TEM) 9.2 (XRD)

(magnetite) 100 (coreshell particles)

(magnetite)

µm

10

10

200

**Type of linkage** 

Hydrogen bond

140-230 Furlan et al., 2010

100 Chang et al.,

Covalent bond

Covalent bond Hydrogen bond

Covalent bond

40-60 Feng et al.,

50-80 Girginova et al., 2010

5.7-9.3 Korolev et al., 2002

**Reference** 

Burke et al., 2002

Jain et al., 2005

2007

2008

2009

2008

Andriola Silva et al.,

Kobayashi et al.,

Zhang et al., 2002

Kim et al., 2002

homogenous suspensions named ferrofluids (Shen et al., 2004).

Polyisobutylene - all three functionalized with tetraethylenepentamine

Oleic acid, Stearic acid, Linoleic

Double shell with oleic acid - Pluronic F-127, and then entrapped the doxorubicin

Carboxyethylsilanetriol sodium

Ricinoleic acid and Poly(lactic-co-

Double shell: silica (SiO2/Fe3O4)

N-hydroxysuccinimide PEG-

3-aminopropyltrimethoxy silane

and monomethoxy-poly(ethylene

3-aminopropyltrimethoxy silane

and Polyethylene glycol diacid (HOOC–PEG–COOH)

3-aminopropyl) triethoxysilane

CS2, NaOH and 2-propanol

glycolic) acid (PLGA)

and aluminosilicate

Ethoxy-PEGsilane

fluorescein Folic acid

(APTMS)

(APTES)

(APTES)

Table 1. Core-shell magnetite particles.

FeSO4•7H2O Tetraethoxyorthosilicate (TEOS) (OEt)4Si

glycol) (MPEG) (CH3CH2O)3-Si-MPEG

Fe(CO)5 Polyethylene, Polystyrene,

acid

salt solution

**Coating agent Diameter**

Xylan 25.26±0.42

**Magnetite particles precursors** 

FeCl2•4H2O FeCl3•6H2O

FeCl2•4H2O FeCl3•6H2O

FeCl3•6H2O FeSO4•6H2O

FeCl2•4H2O FeCl3•6H2O

FeCl2•4H2O FeCl3•6H2O

FeCl2•4H2O FeCl3•6H2O

FeCl2•4H2O FeCl3•6H2O

FeCl3•6H2O FeSO4•7H2O

FeCl3 Na2SO3

FeSO4 FeCl3

The influence of ionic species concentrations on the properties of magnetite particles was also followed. It was noted that the Fe2+/Fe3+ molar ratio was a determining factor in obtaining sub-micron sizes, while by increasing the ratio, the mean diameter of the magnetic particles increased, but unfortunately the yield decreased (Babes et al., 1999).
