1. Synthesis and stabilisation of the superparamagnetic iron oxide
nanoparticles (SPIONP) sol
Sheong Wei NG
Cologne University of Applied Sciences, Cologne/Germany, 2015
Superparamagnetism (SP)
SP describes the behaviour of certain type
of materials by which large magnetisation
(M) is induced when an external magnetic
field is applied on the materials and the
generated magnetic field has the same
magnetic direction (H) as the external
applied magnetics field. Figure 1 illustrates
the difference between ferromagnetism,
paramagnetism and superparamagnetism.
Nanoparticles exhibit this behaviour at
room temperature.
Stabilisation of the SPIONP sol
Coprecipitated SPIONP can be
electrostatically (a) and sterically (b) stabilised
to prevent agglomeration. Nitric acid (HNO3)
and Tetramethylammonium hydroxide
(TMAOH) electrostatically stabilise SPIONP.
Conclusion
• The SPIONP sol can be synthesised with coprecipitation
method and stabilised with HNO3 or TMAOH.
• The synthesised sols behave like ferrofluid.
• Temperature and ultrasound have no effect on the sols.
• Change of pH of the sols causes the SPIONP to agglomerate.
Because the charged ions, which electrostatically stabilise the
SPIONP, are neutralised by the added oppositely charged ions.
References
[1] Anon: Superparamagnetism: limits and applications, Nanotechnol 7 (2007) 1828-1836
[2] A. Andrade, R. Ferreira, J. Fabris, R. Domingues: Coating nanomagnetic particles for biomedical applications, in B.S. Prof. R. Fazel (Eds): Biomedical engineering – Frontiers
and challenges, InTech, Croatia, 2011, pp. 157-176
Fig. 1: The difference between
ferromagnetism, paramagnetism and superparamagnetism [1]
(a) (b)
Fig. 2: Electrostatic (a) and steric (b) stabilisation of SPIONP [2]
Note:
FeCl3∙6H2O - Iron (III) Chloride
hexahydrate
FeCl2∙4H2O - Iron (II) Chloride
tetrahydrate
Note: HCl – Hydrochloric Acid
Synthesis of HNO3 stabilised SPIONP sol Synthesis of TMAOH stabilised SPIONP sol
Stability of the sols against Ultrasound
Ultrasound
treatment
HNO3 stabilised SPIONP sol TMAOH stabilised SPIONP sol
Ultrasound
treatment
• The sols reacted similarly to the magnet after the ultrasound
treatment.
• Ultrasound has no effect on the sols.
Stability of the sols against Temperature
20 °C 40 °C 60 °C 80 °C
HNO3
stabilised
SPIONP sol
TMAOH
stabilised
SPIONP sol
Temperature
• The sols reacted similarly to the magnet after immersion in
water baths with different temperatures.
• Temperature has no effect on the sols.
Stability of the sols against pH change
HNO3 stabilised SPIONP sol TMAOH stabilised SPIONP sol
Addition of
NaCl
Addition of
HCl
The SPIONP agglomerate after
the addition of sodium chloride
(NaCl). Because the H+ ions from
the HNO3, which electrostatically
stabilised the NP, was neutralised
by the added Cl- ions.
The SPIONP agglomerate after
the addition of HCl. Because the
OH- ions from the TMAOH,
which electrostatically stabilised
the NP, was neutralised by the
added H+ ions.
MS : Saturation magnetisation
MR : Remanent magnetisation
Ferromagnetism
Paramagnetism
Superparamagnetism
FeCl3•6H2O
2.16 g
FeCl2•4H2O
0.795 g
Distilled water
100 ml
Dispersion with
black precipitate
Ammonium
hydroxide
5 ml
Under
stirring
Black precipitate
Seperation with
magnet
Black precipitate
Wash with distilled
water (3X)
Black sol
(Ferrofluid)
Distilled water 10 ml
1 M HNO3 10 ml
1 M FeCl3•6H2O
(in 2 M HCl)
10 ml
2 M FeCl2•4H2O
(in 2 M HCl)
2.5 ml
Orange solution
Sol with black
precipitate
TMAOH
(25 % w/w)
21 ml
Under
stirring
Black sol
(Ferrofluid)