Surface Charge and Coating of CoFe2O4 Nanoparticles: Evidence of ...
Surface Charge and Coating of CoFe2O4 Nanoparticles: Evidence of Preserved Magnetic and Electronic Properties Silvia Nappini,a* Elena Magnano,aFederica Bondino,aIgor Píš,a,bAlessandro Barla,c Elvira Fantechi,d Francesco Pineider,d Claudio Sangregorio,e Lisa Vaccari,bLeonardo Venturelli,a and Piero Baglionif. a
IOM CNR, Laboratorio TASC, S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
b
Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
c
Istituto di Struttura della Materia, ISM CNR, S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
d
e
INSTM and Department of Chemistry, via della Lastruccia 3, 50019 Sesto F.no, Florence, Italy
INSTM and ICCOM CNR, Via Madonna del Piano 10, 50019 Sesto F.no, Florence, Italy
f
CSGI and Department of Chemistry, via della Lastruccia 3, 50019 Sesto F.no, Florence, Italy
Concentration of NP solutions..............................................................................2 XAS spectra O K-edge...........................................................................................3 XPS spectra of Fe 2p and Co 2p...........................................................................4 XPS spectra in the O 1s region.............................................................................5 Sum rules: p, q, r parameters from XMCD and XAS spectra integration......6 Magnetic hysteresis loops measured at T = 310 K on solid pellets....................8 References...............................................................................................................9
1
Concentration of NP solutions
Table S1. Concentration of the alkaline (negative), acidic (positive) and citrate coated MNP aqueous solution after the chemical synthesis obtained by ICP-AES analysis
Concentration (mg/ml)
Citrate coated CoFe2O4
Uncoated CoFe2O4(-)
Uncoated CoFe2O4(+)
16.5±0.5
70.0±2.1
35.0±1.0
2
XAS spectra O K-edge
Figure S1. O-K edge XAS spectra of negatively and positively charged uncoated, and citrate coated CoFe2O4 NPs recorded both in TEY (blue curve) and TFY (red curve) mode. The features in the pre-edge region (530-534 eV) correspond to partial covalent Fe-O and Co-O bonds, where O 2p hybridize with Fe and Co 3d orbitals1–3. In this region, the ligand to metal charge transfer excitations to unoccupied Fe and Co 3d states are split by the crystal field of the distorted octahedral coordination geometry. The broad band between 536 and 544 eV is attributed to hybridization of the O 2p with the Fe and Co 4sp states2. At higher energy, a specific feature of metal oxide appears around 548 eV, and it can be assigned to multiple scattering (MS) resonance between an emitter oxygen atom and the nearest oxygen neighbors4. The MS region is sensitive to atomic geometry through the impact of structure on the upper conduction band and it is a clear evidence of iron oxide NPs4.
3
XPS spectra of Fe 2p and Co 2p
Figure S2. XPS spectra of the Fe 2p (a) and Co 2p (b) core levels of positively (red curve), negatively (green curve) and citrate coated (blue curve) CoFe2O4 NPs. 4
XPS spectra in the O 1s region
Figure S3. XPS spectra for O1s of positively, negatively, citrate coated CoFe2O4 NPs, and SiO2 wafer.
5
Sum rules: p, q, r parameters from XMCD and XAS spectra integration
Figure S4. Calculated XMCD spectra and corresponding integration curves at 11 K upon a magnetic field of 2 T, and at 150 K in remanent magnetization of Fe (a) and Co L23 edges (b) .
6
Figure S5. Calculated XAS spectra and corresponding integration curves of Fe (a) and Co L23 edges (b) .
7
Magnetic hysteresis loops measured at T = 310 K on solid pellets
1.0
Negative Positive Citrate
M/M60000 Oe
0.5
0.0
-0.5 0
-1.0 -3000 -2000 -1000
-60000
-40000
-20000
0
20000
0
1000 2000 3000
40000
60000
Magnetic Field (Oe) Figure S6. Magnetic hysteresis loops measured at T = 310 K on solid pellets of the three NP samples. Magnetic moment values are normalized to saturation. Inset: zoom on the low field area of the loops.
8
References 1. Sherman, D. M. Electronic structures of iron(III) and manganese(IV) (hydr)oxide minerals: Thermodynamics of photochemical reductive dissolution in aquatic environments. Geochim. Cosmochim.
Acta 69, 3249–3255 (2005). 2. Groot, F. M. F. de et al. Oxygen 1s and cobalt 2p X-ray absorption of cobalt oxides. J. Phys. Condens.
Matter 5, 2277 (1993). 3. Cao, C.-Y. et al. Low-Cost Synthesis of Flowerlike α-Fe2O3 Nanostructures for Heavy Metal Ion Removal: Adsorption Property and Mechanism. Langmuir 28, 4573–4579 (2012). 4. Moussy, J.-B. From epitaxial growth of ferrite thin films to spin-polarized tunnelling. J. Phys. Appl. Phys.
46, 143001 (2013).
9
IOM CNR, Laboratorio TASC, S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
b
Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
c
Istituto di Struttura della Materia, ISM CNR, S.S. 14 km 163.5, 34149 Basovizza, Trieste, Italy
d
e
INSTM and Department of Chemistry, via della Lastruccia 3, 50019 Sesto F.no, Florence, Italy
INSTM and ICCOM CNR, Via Madonna del Piano 10, 50019 Sesto F.no, Florence, Italy
f
CSGI and Department of Chemistry, via della Lastruccia 3, 50019 Sesto F.no, Florence, Italy
Concentration of NP solutions..............................................................................2 XAS spectra O K-edge...........................................................................................3 XPS spectra of Fe 2p and Co 2p...........................................................................4 XPS spectra in the O 1s region.............................................................................5 Sum rules: p, q, r parameters from XMCD and XAS spectra integration......6 Magnetic hysteresis loops measured at T = 310 K on solid pellets....................8 References...............................................................................................................9
1
Concentration of NP solutions
Table S1. Concentration of the alkaline (negative), acidic (positive) and citrate coated MNP aqueous solution after the chemical synthesis obtained by ICP-AES analysis
Concentration (mg/ml)
Citrate coated CoFe2O4
Uncoated CoFe2O4(-)
Uncoated CoFe2O4(+)
16.5±0.5
70.0±2.1
35.0±1.0
2
XAS spectra O K-edge
Figure S1. O-K edge XAS spectra of negatively and positively charged uncoated, and citrate coated CoFe2O4 NPs recorded both in TEY (blue curve) and TFY (red curve) mode. The features in the pre-edge region (530-534 eV) correspond to partial covalent Fe-O and Co-O bonds, where O 2p hybridize with Fe and Co 3d orbitals1–3. In this region, the ligand to metal charge transfer excitations to unoccupied Fe and Co 3d states are split by the crystal field of the distorted octahedral coordination geometry. The broad band between 536 and 544 eV is attributed to hybridization of the O 2p with the Fe and Co 4sp states2. At higher energy, a specific feature of metal oxide appears around 548 eV, and it can be assigned to multiple scattering (MS) resonance between an emitter oxygen atom and the nearest oxygen neighbors4. The MS region is sensitive to atomic geometry through the impact of structure on the upper conduction band and it is a clear evidence of iron oxide NPs4.
3
XPS spectra of Fe 2p and Co 2p
Figure S2. XPS spectra of the Fe 2p (a) and Co 2p (b) core levels of positively (red curve), negatively (green curve) and citrate coated (blue curve) CoFe2O4 NPs. 4
XPS spectra in the O 1s region
Figure S3. XPS spectra for O1s of positively, negatively, citrate coated CoFe2O4 NPs, and SiO2 wafer.
5
Sum rules: p, q, r parameters from XMCD and XAS spectra integration
Figure S4. Calculated XMCD spectra and corresponding integration curves at 11 K upon a magnetic field of 2 T, and at 150 K in remanent magnetization of Fe (a) and Co L23 edges (b) .
6
Figure S5. Calculated XAS spectra and corresponding integration curves of Fe (a) and Co L23 edges (b) .
7
Magnetic hysteresis loops measured at T = 310 K on solid pellets
1.0
Negative Positive Citrate
M/M60000 Oe
0.5
0.0
-0.5 0
-1.0 -3000 -2000 -1000
-60000
-40000
-20000
0
20000
0
1000 2000 3000
40000
60000
Magnetic Field (Oe) Figure S6. Magnetic hysteresis loops measured at T = 310 K on solid pellets of the three NP samples. Magnetic moment values are normalized to saturation. Inset: zoom on the low field area of the loops.
8
References 1. Sherman, D. M. Electronic structures of iron(III) and manganese(IV) (hydr)oxide minerals: Thermodynamics of photochemical reductive dissolution in aquatic environments. Geochim. Cosmochim.
Acta 69, 3249–3255 (2005). 2. Groot, F. M. F. de et al. Oxygen 1s and cobalt 2p X-ray absorption of cobalt oxides. J. Phys. Condens.
Matter 5, 2277 (1993). 3. Cao, C.-Y. et al. Low-Cost Synthesis of Flowerlike α-Fe2O3 Nanostructures for Heavy Metal Ion Removal: Adsorption Property and Mechanism. Langmuir 28, 4573–4579 (2012). 4. Moussy, J.-B. From epitaxial growth of ferrite thin films to spin-polarized tunnelling. J. Phys. Appl. Phys.
46, 143001 (2013).
9
