**6. XPS results for core-shell magnetic nanoparticles**

160 Materials Science and Technology

magnetic microparticles were obtained (Andriola Silva et al., 2007) to protect magnetite

The aim of the catalysis is to search new catalysts that can be recovered when their activity is ended (Sankaranarayanapillai et al., 2010). The magnetic dispersions are attractive in separation applications as they offer high surface area and can be functionalized to apply to different molecular or cellular species. The magnetic fluids can be used as magnetically separable nanocatalytic systems that combine the advantages of homogeneous and heterogeneous catalysis (Lu et al., 2004). Novel thermoreversible magnetic fluids based on magnetite (Fe3O4) coated with a covalently anchored polymeric shell of poly(2-methoxyethyl methacrylate) (PMEMA) were synthesized by surface-initiated ATRP (Gelbrich et al., 2006). The coated particles form stable dispersions in methanol at temperatures above an upper

Magnetically recoverable heterogenized nanoparticle supported chiral Ru complexes were obtained and used in highly enantioselective asymmetric hydrogenation of aromatic ketones (Hu et al., 2005). The catalysts can be recycled by magnetic decantation and used for asymmetric hydrogenation for up to 14 times without loss of activity and enantioselectivity.

Ferofluids have numerous applications in rotary and linear seals as magneto transformers, sensors and pressure transducers (flow speed), inertial sensors (acceleration, inclination, and gravity) (Vekas, 2008), passive and active bearings, vibration dampers, linear and rotary drives, and chemical industry (microtechnologies) as chips, etc. Among the most important and commercial applications are developed magnetofluids rotating seals, which are found today in a variety of equipments, in electronics, nuclear industry, biotechnology, aeronautics

Magnetofluids sealing advantages compared with mechanical seals are: sealing without leaking, life time (~ 5 years), only viscous friction, zero contamination, field operation (high vacuum (10-8 mbar) at approx. 10 bar), relatively simple construction and low

For seals in dynamic regime, ferrofluids must obey a series of requirements (www.roseal.topnet.ro): high saturation magnetization (up to 50 kA/m (approx. 600 g)), physical properties adapted to operating conditions, especially in gas pressure and temperature sealed, high colloidal stability in intense and powerful magnetic field,

Ferrofluids should operate at 1500C in continuous system or at temperatures of 2000C in intermittent system. They should also work in winter conditions (-200C) or in space

Researchers at NASA (Rosensweig et al., 1985) experienced ferrofluids in a spacecraft control system. While ferrofluids are used often in commercial processes, for the manufacture of CDs to create sophisticated suspension systems for cars, a researcher at

from gastric dissolution.

**5.2 Applications in catalysis** 

critical solution temperature.

**5.3 Industrial applications** 

and space applications.

manufacturing cost (www.roseal.topnet.ro).

Newtonian flow properties even in intense magnetic field.

environment (-550C) and to resist at nuclear radiation.

Magnetite particles coated by different Si-containing compounds (monomers and polymers) were prepared using co-precipitation method or a free-solvent synthesis. The covered magnetite particles were obtained in one step by co-precipitation of iron chloride salts in presence of monomers or (co)polymers adequately functionalized, as surfactants. When the co-precipitation was in the absence of surfactant, the covered particles were obtained in two steps, the first step consisting in the obtaining of magnetite particles and in the second step, the magnetite particles being covered with an adequate monomer or (co)polymer, specific for the desired application. The magnetite particles covered with aminosilane were obtained by replacement of the shell of magnetite-oleic acid particles which were synthesised by a free-solvent method. The average diameters of magnetic nanoparticles are depending on the synthesis method, are less than 1 µm and the smallest dimensions are obtained by freesolvent method (Table 2).

In this chapter we focused on the characterization of core-shell magnetic nanoparticles as determined by X-ray photoelectron spectroscopy (XPS). XPS, also known as Electron Spectroscopy for Chemical Analysis (ESCA), is an elemental analysis technique and used to determine quantitatively the atomic composition and surface chemistry. XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top 1 to 10 nm of the material being analysed (Watts et al., 2003; http://en.wikipedia.org/wiki/Xray\_photoelectron\_spectroscopy).

The surface of the magnetite particles modified with aminosilane (Ma-APTES) or with polydimethylsiloxane–carboxy-terminated poly(ethylene oxide) graft copolymer (Ma-PDMSgPEO-COOH) was carefully followed using XPS data.

Hydrophilic magnetite particles (Ma-APTES) were prepared by two methods:


DLS, SEM and AFM analysis indicated the formation of low polydispersity particles, with a spherical morphology and dimensions of nanometers (Table 2).

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 163

Table 2. Coated magnetite particles.

Fig. 6. Schematic principle of covalent bonding between magnetite core and ethoxyl groups of silane monomer (Durdureanu-Angheluta et al., 2008).

Fig. 7. Schematic representation of replacement of oleic acid shell with aminosilane monomer from magnetite-oleic acid particles (Durdureanu-Angheluta et al., 2011b).

Fig. 6. Schematic principle of covalent bonding between magnetite core and ethoxyl groups

Fig. 7. Schematic representation of replacement of oleic acid shell with aminosilane monomer from magnetite-oleic acid particles (Durdureanu-Angheluta et al., 2011b).

of silane monomer (Durdureanu-Angheluta et al., 2008).


Table 2. Coated magnetite particles.

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 165

C 1s (Figure 8) has two clear peaks, and requires three for a good fit. These have been assigned to C-C, C-O/C-N (should really be at least 2 peaks) and a weak peak tentatively assigned to O-C=O. N 1s (Figure 8) has two peaks, which appear to represent amine and ammonium (or ammonia) in the sample. O 1s (Figure 8) has three peaks, probably from different C-O and Si-O states, and also an inorganic oxide which is presumably the magnetite. Fe 2p (Figure 8) is extremely weak, so it is difficult to confirm the iron chemistry

The structure of Ma-APTES2 coated magnetite nanoparticles (Table 2) was demonstrated by X-ray photoelectron spectroscopy (XPS), showing the formation of chemical bonds between the surface of magnetite particles and the oxygen atoms of the shells (Durdureanu-Angheluta et al., 2011b). XPS was performed on a KRATOS Axis Nova (Kratos Analytical, Manchester, United Kingdom), using AlKα radiation, with 20 mA current and 15 kV voltage (300 W), and base pressure of 10-8 to 10-9 Torr in the sample chamber. The incident monochromated X-ray beam was focused on a 0.7 mm x 0.3 mm area of the surface. The XPS survey spectra for the magnetite sample was collected in the range of -5÷1200 eV with a resolution of 1 eV and a pass energy of 160 eV. The high resolution spectra for all the elements identified from the survey spectra were collected using pass energy of 20 eV and a step size of 0.1 eV. The data were analyzed using the Vision Processing software (Vision2 software, Version 2.2.8). A linear background was subtracted before the peak areas were

In Figure 9 the peak at 283.4 eV belonging to the carbon from C-Si, 285.2 eV, was assigned to the carbon in the aliphatic chain (C-C) and the peak at 286.6 eV was ascribed to the carbon from C-N. The others two small peaks at 287.9 and 289.2 eV belonging to the carboxylate

al., 2006), and come from traces of oleic acid. The lack of peak at 290 eV indicates the absence of free oleic acid. The bonding energies at 102.3 and 103.0 eV (Figure 10) were the characteristic peaks from Si-O and Si-C bonds, respectively. Deconvolution of the N 2p peaks (Figure 11) indicated, at 399.3 and 400.8 eV, the presence of amino groups (NH2) and tertiary amino groups, respectively. From the deconvolution of O 1s peaks (Figure 12) resulted three peaks from magnetite (around 530.8 eV), HO-Fe (around 531.4 eV) (Khurshid et al., 2009) and O-Si oxygen bonds (around 532.4 eV). The peak at around 535 eV could be due to the traces of oleic acid in the layer. The bonding energies at 710.6 and 723.7 eV were the characteristic peaks from Fe 2p3/2 and Fe 2p1/2, respectively. Deconvolution of the Fe 2p has shown the presence of Fe3+ and Fe2+ in both Fe 2p2/3 and Fe 2p1/2 regions (Fe3+ 2p2/3/Fe3+ 2p1/2: 710.7 eV/724.4 eV; Fe2+ 2p2/3/Fe2+ 2p1/2: 709.2 eV/722 eV). It should be mention that an energy difference of 13.1 eV between 2p3/2 and 2p1/2 peaks indicates that the material has, as dominant phase, Fe3O4 and, as secondary phase, siloxy-Fe and carboxylate-Fe bonds (Zhang et al., 2006). Also, XPS results on the Fe2+/Fe3+ molar ratio of 0.13 (Figure 13) confirm the Fe2+/Fe3+ molar ratio used in the synthesis of the magnetite particles (Ma-OA from

Hydrophobic magnetite particles (Ma-PDMSgPEO-COOH) were obtained by coprecipitation of iron salts in water at pH around 11 in the presence of dichloromethane

Dimensional analysis of magnetite particles coated with PDMSgPEO-COOH (Table 2) showed core-shell morphology of an approximate spherical shape, with an average

solution of siloxane copolymer (PDMSgPEO-COOH) (Figure 10) (Pricop et al., 2010).

), were in agreement with the data obtained in the previous literature (Zhang et

corrected. The binding energy of the C 1s peak was normalized to 285 eV.

in more detail than "oxide".

(C=O, COO-

Table 2).

The XPS spectra for Ma-APTES1 (Table 2 and Figure 6) were recorded on a XR6 monochromated X-ray source (Thermo Scientific Escalab250Xi), with AlKalpha radiation and a variable 200-900 µm spot size. Charge correction was performed using C1s at 284.8 eV as a reference. The presence of C 1s, O 1s, Si 2p, N 1s, as well Fe 2p peaks in XPS spectra on Ma-APTES1 sample give a proof for the chemical structure of aminopropyltrisiloxy coated magnetite particles. The Si 2p spectrum (Figure 8) has a peak at 102.4 eV, which is typical of silicone atoms, but is also consistent with the oxysilane group expected in the sample.

Fig. 8. High-resolution Si 2p, C 1p, N 1s, O 1s and Fe 2p XPS spectra for Ma-APTES1 from Table 2.

The XPS spectra for Ma-APTES1 (Table 2 and Figure 6) were recorded on a XR6 monochromated X-ray source (Thermo Scientific Escalab250Xi), with AlKalpha radiation and a variable 200-900 µm spot size. Charge correction was performed using C1s at 284.8 eV as a reference. The presence of C 1s, O 1s, Si 2p, N 1s, as well Fe 2p peaks in XPS spectra on Ma-APTES1 sample give a proof for the chemical structure of aminopropyltrisiloxy coated magnetite particles. The Si 2p spectrum (Figure 8) has a peak at 102.4 eV, which is typical of silicone atoms, but is also consistent with the oxysilane group expected in the sample.

Fig. 8. High-resolution Si 2p, C 1p, N 1s, O 1s and Fe 2p XPS spectra for Ma-APTES1 from

Table 2.

C 1s (Figure 8) has two clear peaks, and requires three for a good fit. These have been assigned to C-C, C-O/C-N (should really be at least 2 peaks) and a weak peak tentatively assigned to O-C=O. N 1s (Figure 8) has two peaks, which appear to represent amine and ammonium (or ammonia) in the sample. O 1s (Figure 8) has three peaks, probably from different C-O and Si-O states, and also an inorganic oxide which is presumably the magnetite. Fe 2p (Figure 8) is extremely weak, so it is difficult to confirm the iron chemistry in more detail than "oxide".

The structure of Ma-APTES2 coated magnetite nanoparticles (Table 2) was demonstrated by X-ray photoelectron spectroscopy (XPS), showing the formation of chemical bonds between the surface of magnetite particles and the oxygen atoms of the shells (Durdureanu-Angheluta et al., 2011b). XPS was performed on a KRATOS Axis Nova (Kratos Analytical, Manchester, United Kingdom), using AlKα radiation, with 20 mA current and 15 kV voltage (300 W), and base pressure of 10-8 to 10-9 Torr in the sample chamber. The incident monochromated X-ray beam was focused on a 0.7 mm x 0.3 mm area of the surface. The XPS survey spectra for the magnetite sample was collected in the range of -5÷1200 eV with a resolution of 1 eV and a pass energy of 160 eV. The high resolution spectra for all the elements identified from the survey spectra were collected using pass energy of 20 eV and a step size of 0.1 eV. The data were analyzed using the Vision Processing software (Vision2 software, Version 2.2.8). A linear background was subtracted before the peak areas were corrected. The binding energy of the C 1s peak was normalized to 285 eV.

In Figure 9 the peak at 283.4 eV belonging to the carbon from C-Si, 285.2 eV, was assigned to the carbon in the aliphatic chain (C-C) and the peak at 286.6 eV was ascribed to the carbon from C-N. The others two small peaks at 287.9 and 289.2 eV belonging to the carboxylate (C=O, COO-), were in agreement with the data obtained in the previous literature (Zhang et al., 2006), and come from traces of oleic acid. The lack of peak at 290 eV indicates the absence of free oleic acid. The bonding energies at 102.3 and 103.0 eV (Figure 10) were the characteristic peaks from Si-O and Si-C bonds, respectively. Deconvolution of the N 2p peaks (Figure 11) indicated, at 399.3 and 400.8 eV, the presence of amino groups (NH2) and tertiary amino groups, respectively. From the deconvolution of O 1s peaks (Figure 12) resulted three peaks from magnetite (around 530.8 eV), HO-Fe (around 531.4 eV) (Khurshid et al., 2009) and O-Si oxygen bonds (around 532.4 eV). The peak at around 535 eV could be due to the traces of oleic acid in the layer. The bonding energies at 710.6 and 723.7 eV were the characteristic peaks from Fe 2p3/2 and Fe 2p1/2, respectively. Deconvolution of the Fe 2p has shown the presence of Fe3+ and Fe2+ in both Fe 2p2/3 and Fe 2p1/2 regions (Fe3+ 2p2/3/Fe3+ 2p1/2: 710.7 eV/724.4 eV; Fe2+ 2p2/3/Fe2+ 2p1/2: 709.2 eV/722 eV). It should be mention that an energy difference of 13.1 eV between 2p3/2 and 2p1/2 peaks indicates that the material has, as dominant phase, Fe3O4 and, as secondary phase, siloxy-Fe and carboxylate-Fe bonds (Zhang et al., 2006). Also, XPS results on the Fe2+/Fe3+ molar ratio of 0.13 (Figure 13) confirm the Fe2+/Fe3+ molar ratio used in the synthesis of the magnetite particles (Ma-OA from Table 2).

Hydrophobic magnetite particles (Ma-PDMSgPEO-COOH) were obtained by coprecipitation of iron salts in water at pH around 11 in the presence of dichloromethane solution of siloxane copolymer (PDMSgPEO-COOH) (Figure 10) (Pricop et al., 2010).

Dimensional analysis of magnetite particles coated with PDMSgPEO-COOH (Table 2) showed core-shell morphology of an approximate spherical shape, with an average

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 167

Fig. 11. High-resolution N 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-

Fig. 12. High-resolution O 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-

Angheluta et al., 2011b).

Angheluta et al., 2011b)

Fig. 9. High-resolution C 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-Angheluta et al., 2011b).

Fig. 10. High-resolution Si 2p XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-Angheluta et al., 2011b).

Fig. 9. High-resolution C 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-

Fig. 10. High-resolution Si 2p XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-

Angheluta et al., 2011b).

Angheluta et al., 2011b).

Fig. 11. High-resolution N 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-Angheluta et al., 2011b).

Fig. 12. High-resolution O 1s XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-Angheluta et al., 2011b)

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 169

Fig. 14. Schematic principle of hydrogen bonding between magnetic core and the

magnetization values are correlated with those reported by the literature.

The core-shell magnetic particles present superparamagnetic properties and their saturation

hydrophobic siloxane shell.

Fig. 13. High-resolution Fe 2p XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-Angheluta et al., 2011b)

diameter of 500 nm. The amphiphilic graft copolymer was proved to be efficient as surfactant in the preparation of magnetite particles with a hydrophobic siloxane shell (Pricop et al., 2010).

Ma-PDMSgPEO-COOH particles were analysed on the AXIS Nova X-ray photoelectron spectrometer built around the AXIS technology. Data reduction and processing was performed using Kratos' Vision 2 Processing software.

XPS scans of Si 2p atoms evidenced the appearance of the peaks at around 100 and 102 eV, characteristic for Si-O and Si-C bonds, respectively (Figure 15). C 1s atoms present specific peaks for CH3-Si, CH2-Si, C-O-C, C-C, C=O, O-C=O (Figure 15) in the 282 to 289 eV interval. The deconvolution of O 1s shows the presence of the peak at around 530 eV (Figure 15), corresponding to the metallic oxide and the presence of two peaks, with higher binding energies due to hydroxyl groups or from the coating of the sample. The deconvolution of Fe 2p atoms (Figure 15) presents two peaks at 710.7 and 712.8 eV, attributed to Fe3+ 2p2/3 and Fe2+ 2p2/3,respectively.

The presence of peaks at 724.0 and 726.0 eV of Fe3+ 2p1/2 and Fe2+ 2p1/2, respectively and the difference of 13.2 eV between Fe 2p3/2 and Fe 2p1/2 explain the presence of the carboxylate-Fe bonds (Zhang et. al., 2006).

It should be underlined that the XPS results were substantiated by FT-IR data, indicating the formation of the hydrogen or covalent bonds between the iron oxide substrate and the functional group of the surfactant.

Fig. 13. High-resolution Fe 2p XPS spectra for Ma-APTES2 from Table 2 (Durdureanu-

diameter of 500 nm. The amphiphilic graft copolymer was proved to be efficient as surfactant in the preparation of magnetite particles with a hydrophobic siloxane shell

Ma-PDMSgPEO-COOH particles were analysed on the AXIS Nova X-ray photoelectron spectrometer built around the AXIS technology. Data reduction and processing was

XPS scans of Si 2p atoms evidenced the appearance of the peaks at around 100 and 102 eV, characteristic for Si-O and Si-C bonds, respectively (Figure 15). C 1s atoms present specific peaks for CH3-Si, CH2-Si, C-O-C, C-C, C=O, O-C=O (Figure 15) in the 282 to 289 eV interval. The deconvolution of O 1s shows the presence of the peak at around 530 eV (Figure 15), corresponding to the metallic oxide and the presence of two peaks, with higher binding energies due to hydroxyl groups or from the coating of the sample. The deconvolution of Fe 2p atoms (Figure 15) presents two peaks at 710.7 and 712.8 eV, attributed to Fe3+ 2p2/3 and

The presence of peaks at 724.0 and 726.0 eV of Fe3+ 2p1/2 and Fe2+ 2p1/2, respectively and the difference of 13.2 eV between Fe 2p3/2 and Fe 2p1/2 explain the presence of the carboxylate-

It should be underlined that the XPS results were substantiated by FT-IR data, indicating the formation of the hydrogen or covalent bonds between the iron oxide substrate and the

Angheluta et al., 2011b)

(Pricop et al., 2010).

Fe2+ 2p2/3,respectively.

Fe bonds (Zhang et. al., 2006).

functional group of the surfactant.

performed using Kratos' Vision 2 Processing software.

Fig. 14. Schematic principle of hydrogen bonding between magnetic core and the hydrophobic siloxane shell.

The core-shell magnetic particles present superparamagnetic properties and their saturation magnetization values are correlated with those reported by the literature.

Tailored and Functionalized Magnetite Particles for Biomedical and Industrial Applications 171

Asmatulu, R.; Zalichb, M.A.; Clausa, R.O. & Riffle, J.S. (2005), Synthesis, characterization

Babes, L.; Denizot, B.; Tanguy, G.; Le Jeune, J.J. & Jallet, P. (1999), Synthesis of iron oxide

Bagwe, R.P.; Kanicky, J.R; Palla, B.J.; Patanjali, P.K. & Shah, D.O. (2001), Improved drug

Beckera, C.; Hodenius, M.; Blendinger, G.; Sechi, A.; Hieronymus, T.; Muller-Schulte, D.;

Bee, A.; Massart, R. & Neveu, S. (1995), Synthesis of very fine magnetite particles. *J. Magn.* 

Boal, A.K. (2004), Synthesis and application of magnetic nanoparticles, In: *Nanoparticles –* 

Boistelle, R. & Astier, J.P. (1988), Crystallization mechanisms in solution. *J. Cryst. Growth*, 90:

Borrelli, N.F.; Luderer, A.A.; & Panzarino, J.N. (1984), Hysteresis heating for the treatment

Boutry, S.; Laurent, S.; Elst, L.V. & Muller, R.N. (2006), Specific E-selectin targeting with a superparamagnetic MRI contrast agent. *Contrast Med. Mol. Imaging,* 1(1): 15-22. Briggs, R.W.; Wu, Z.; Mladinich, C.R.J.; Stoupis, C.; Gauger, J.; Liebig, T.; Ros, P.R.;

Bulte, J.W. (2006), Intracellular endosomal magnetic labeling of cells, Review. *Methods Mol.* 

Burke, N.; Stover, H. & Dawson, F. (2002), Magnetic nanocomposites: preparation and characterization of polymer-coated iron nanoparticles. *Chem. Mater.,* 14: 4752-4761. Burtea, C.; Laurent, S.; Roch, A.; Elst, L.V. & Muller, R.N. (2005), C-MALISA (cellular

Cai, W. & Wan, J. (2007), Facile synthesis of superparamagnetic magnetite nanoparticles in

Chang, C.F.; Wu, Y.L. & Hou, S.S. (2009), Preparation and characterization of

Chemla, Y.R.; Grossman, H.L.; Poon, Y.; McDermott, R.; Stevens, R.; Alper, M.D. & Clarke, J.

Cornell, R.M. & Schertmann, U. (1991). *Iron Oxides in the Laboratory: Preparation and* 

agent for gastrointestinal MRI. *Magn. Reson. Imaging* 15(5): 559-566.

Bean, C.P. & Livingston, J.D. (1959), Superparamagnetism. *J. Appl. Phys.,* 30: 120-129.

magnetic fields. *J. Magn. Magn. Mater.,* 292: 108-119.

for cell tracking. *J. Magn. Magn. Mater.,* 311: 234-237.

*Rev. Ther. Drug Carrier Syst.*, 18(1): 77-140.

Academic/Plenum Publishers, New York.

of tumours. *Phys. Med. Biol.*, 29: 487–494.

MRI. *J. Inorg. Biochem.*, 99(5): 1135-1144.

liquid polyols. *J. Colloid Interface Sci.,* 305: 366-370.

Surf. A Physicochem. Eng. Aspects, 336: 159-166.

*Characterization.* VCH Publishers: Weinheim, Germany.

and targeting of biodegradable magnetic nanocomposite particles by external

nanoparticles used as MRI contrast agents: A parametric study. *J. Colloid Interface* 

delivery using microemulsions: rationale, recent progress, and new horizons. *Crit.* 

Schmitz-Rode, T. & Zenke, M. (2007), Uptake of magnetic nanoparticles into cells

*Building blocks for nanotechnology.* Rotello V. (ed)*,* pp 1–27, Kluwer

Ballinger, J.R. & Kubilis, P. (1997), In vivo animal tests of an artifact-free contrast

magnetic-linked immunosorbent assay), a new application of cellular ELISA for

superparamagnetic nanocomposites of aluminosilicate/silica/magnetite. Colloids

(2000), Ultrasensitive magnetic biosensor for homogenous assay. *Proc. Natl. Acad.* 

**9. References** 

*Sci.,* 212(2) : 474-482.

*Magn. Mater.*, 149: 6-9.

*Med.*, 124: 419-439.

*Sci.,* 97: 14268-14272.

14-30.

Fig. 15. High-resolution C 1s, Fe 2p, O 1s and Si 2p spectra for Ma-PDMSgPEO-COOH from Table 2.
