The paper describes the differences between wet iron removal from carbon nanoonions and from multiwall carbon nanotubes for analytical purpose. Nowadays, both carbon nanoonions and multiwall carbon nanotubes are one of the most interesting materials with applicability in electronics, medicine and biotechnology. Medical applications of those nanomaterials require not only recognition of their structure but also measurement of metal impurities concentration. Inductively coupled plasma optical emission spectrometry as a method for Fe-determination requires liquid samples. Hence, we propose various protocols for leaching of iron from studied materials. Our results proved that structure of nanomaterials have an impact on the efficiency of iron removal

Bok-Badura, J.

Boncel, S.

Ceglarski, P.

Jakóbik-Kolon, A.

Karoń, K.

Laskowski, J.

Turek, M.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 4 No 2, 02CBNM03(3pp) (2015) 
 
 
2304-1862/2015/4(2)02CBNM03(3) 02CBNM03-1  2015 Sumy State University 
Differences in Iron Removal from Carbon Nanoonions and Multiwall  
Carbon Nanotubes for Analytical Purpose 
 
J. Bok-Badura1*, A. Jakóbik-Kolon1, M. Turek1, S. Boncel1, K. Karoń1, J. Laskowski2, P. Ceglarski2 
 
1 Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego 6, 44-100 Gliwice, Poland 
2 Winiplast, Laboratory of Nanotechnology, Wiosny Ludów 28a, 43-180 Orzesze, Poland  
 
(Received 01 June 2015; published online 24 August 2015) 
 
The paper describes the differences between wet iron removal from carbon nanoonions and from mul-
tiwall carbon nanotubes for analytical purpose. Nowadays, both carbon nanoonions and multiwall carbon 
nanotubes are one of the most interesting materials with applicability in electronics, medicine and bio-
technology. Medical applications of those nanomaterials require not only recognition of their structure but 
also measurement of metal impurities concentration. Inductively coupled plasma optical emission spec-
trometry as a method for Fe-determination requires liquid samples. Hence, we propose various protocols 
for leaching of iron from studied materials. Our results proved that structure of nanomaterials have an 
impact on the efficiency of iron removal. 
 
Keywords: Multiwall carbon nanotubes, Carbon nanoonions, Iron, ICP-OES. 
 
 PACS numbers: 81.07.De, 81.05.Tp, 81.70.Jb 
 
 
                                                          
* Joanna.Bok-Badura@polsl.pl   
1. INTRODUCTION 
 
Multiwall carbon nanotubes (MWCNTs) since their 
discovery have been one of the most interesting mate-
rials in science. This is due to their unique properties 
(chemical, mechanical, magnetic and electronic) [1–3]. 
Another interesting material which exhibits similar to 
MWCNTs properties are carbon nanoonions (CNOs). 
Both MWCNTs and CNOs can be used in optics and 
electronics but also in biotechnology and medicine [4,5]. 
Synthesis of CNTs and CNOs often requires metal 
catalyst (e.g. Fe, Mo, Co, Ni and others) which usually 
remain in the products as impurities. But also, some 
elements are deliberately introduced into the nano-
materials structure in order to add to them special 
properties [6]. The presence of metal nanoparticles in 
CNTs and CNOs – both as contaminants and modifiers 
– should be conveniently monitored, especially as for 
medical application.  
There were a few methods already proposed for iron 
content determination in MWCNTs: instrumental neu-
tron activation analysis (INAA) [1], inductively coupled 
plasma mass spectrometry (ICP-MS) [7], thermogravi-
metric analysis (TGA) [8,9], X-ray photoelectron spec-
troscopy (XPS) [9], scanning electron microsco-
py/energy-dispersive X-ray spectrometry (SEM/EDX) 
[8,9], transmission electron microscopy/ energy-
dispersive X-ray spectrometry (TEM/EDX) [9], induc-
tively coupled plasma optical emission spectrometry 
ICP-OES [10] whereas for CNOs only three: TEM, XRD 
and TGA [11,12]. Most of these methods are only quali-
tative or semi-quantitative and they do not provide 
information about concentration or the results are only 
estimated. In methods such as ICP-OES or ICP-MS, 
which could give full information on particular ele-
ments concentration, liquid samples are required. 
However, because of the extreme difficulties in destruc-
tion of carbon nanomaterials structure – procedures of 
sample pretreatment constitute the most obstacle step 
in such analysis. Dry ashing coupled with acid extrac-
tion, wet digestion, combination of dry ashing with acid 
digestion and microwave-assisted digestion as a 
MWCNTs sample pretreatment protocol for ICP-MS 
were already proposed [7]. These methods are time-
consuming, laborious, and multistage. They also re-
quire the use of aggressive chemicals and conditions 
and depend on the type and structure of materials. In 
addition, they not always ensure complete extraction of 
the interesting element. This behavior can cause some 
mistakes in the further analysis. A use of MWCNTs or 
CNOs certified reference materials would be the most 
appropriate procedure to estimate the efficiency of iron 
removal. Unfortunately, such materials have not been 
yet available since a huge variety of molecular archi-
tectures of these carbon nanostructures were synthe-
sized under a range of different conditions. 
In this paper we propose a method of removing iron 
from the CNOs as an sample pretreatment protocol for 
the ICP-OES analysis. In addition, the same experi-
ments were conducted for MWCNTs to present similar-
ities and differences in the behavior of these materials 
under different conditions.  
 
2. EXPERIMENTAL  
 
2.1 Materials and reagents 
 
MWCNTs and CNOs were synthesized via catalytic 
chemical vapor deposition (c-CVD). MWCNTs were 
obtained according to a procedure previously described, 
briefly at 760 °C using FeCp2 as iron precursor, toluene 
as carbon source and Ar as carrier gas [13]. In turn, 
CNOs were obtained from hydrogen pre-treated iron 
oxides nanoparticles as catalyst, acetylene as carbon 
source and Ar as carrier gas (800 °C). 
To remove iron from examined material nitric acid 
(65%, Suprapur, Merck), sulfuric acid (98%, Suprapur, 
Merck) were used. For calibration stock standard solu-
tions of Fe (1mg mL-1 in 2% HNO3, CPI International) 
 J. BOK-BADURA, A. JAKÓBIK-KOLON ET AL. PROC. NAP 4, 02CBNM03 (2015) 
 
 
02CBNM03-2 
was used. All solution and samples were prepared with 
using ultrapure water (MilliporeElix 10 System). 
 
2.2 Instrumentation 
 
Scanning electron microscope (Phenom Pro Desktop 
SEM) was used to obtain the micrographs of MWCNTs 
and CNOs.  
All determination of Fe concentrations were per-
formed utilizing Varian 710-ES spectrometer equipped 
with an OneNeb nebulizer (Varian, Australia). Operat-
ing parameters are described in Table 1.  
 
Table 1 – The operating parameters of ICP-OES analysis  
 
RF power, kW 1 
Ar plasma flow rate, 
L min-1 
15 
Ar carrier flow rate, 
L min-1 
1.5 
Nebulizer pressure, 
kPa 
210 
Pump rate, rpm 15 
Viewing axial 
Fe wavelength, nm 234.350, 261.187, 261.382 
 
2.3 Sample pretratment  
 
Five different conditions were chosen to examine 
the extractability of iron from CNOs and MWCNTs: 
water, diluted HNO3, concentrated HNO3, mixture of 
concentrated HNO3 and H2SO4 (4:1) and microwave 
digestion (MARS 5 CEM Corp. 200°C, ramp time 15 
min., hold time 15 min.) in mixture of  concentrated 
HNO3 and H2SO4 (4:1). All the samples, with the excep-
tion of samples for mineralization, were shaken with 
the solution for 12 hours at room temperature using 
the laboratory shaker. After that samples were filtered 
and the obtained solutions were analyzed using ICP-
OES. 
 
3. RESULTS AND DISCUSION  
 
3.1 Structure 
 
Firstly, SEM micrographs of examined materials 
were prepared to compare their structures (see Fig. 1). 
 
 
 
Fig. 1 – SEM image (a), MWCNTs with encapsulated Fe 
catalyst (b), CNOs with encapsulated Fe catalyst 
 
The differences in structure of carbon nanotubes 
and carbon nanoonions  are clearly visible. CNOs have 
a spherical shape with smooth surface in contract to 
the MWCNTs that have the needle-like fiber shape. 
This difference was also visible in product of minerali-
zation. CNOs after mineralization get slurry of small 
particles evenly dispersed in a solution whereas 
MWCNTs gets a slurry of puffed up bundles of a signif-
icantly greater volume (see. Fig. 2). 
 
 
 
Fig. 2 – Slurries after mineralization (a), CNOs (b), MWCNTs  
 
3.2 Determination of iron content in leachate by 
ICP-OES analysis 
 
Iron content in studied CNOs and MWCNTs ob-
tained after leaching with nitric and sulfuric acid in a 
few conditions are presented in Fig. 3a and 3b. Results 
obtained from water solution were omitted because iron 
wasn’t being removed under these conditions.  
 
 
 
Fig. 3 – Iron concentration (ICP-OES) in (a), CNOs (b), 
MWCNTs obtained after using different sample pretreatment: 
A – 5% HNO3, B – conc. HNO3, C – mixture of conc. HNO3 and 
conc. H2SO4 (4:1), D - mixture of conc. HNO3 and conc. H2SO4 
(4:1) and mineralization 
 
The best results for CNOs and MWCNTs were 
measured if diluted nitric acid and microwave  mineral-
ization in mixture of  concentrated nitric and sulfuric 
a b 
a b 
 DIFFERENCES IN REMOVAL IRON CONTENT FROM CARBON NANOONIONS … PROC. NAP 4, 02CBNM03 (2015) 
 
 
02CBNM03-3 
acid were used respectively. When concentrated nitric 
acid was used the obtained results were about half 
lower than when diluted acid was used. It could be due 
to the fact that in concentrated acid iron is rendered 
passive. If 5% HNO3 and mineralization in conc. HNO3 
and H2SO4 were used the highest content of iron was 
removed from CNOs (there is only a 12% difference). 
Otherwise, in the case of MWCNTs difference in ob-
tained results, in mentioned condition, was about 40%. 
This fact may be related to differences in the structure 
of the CNOs and the MWCNTs. Fiber like structure in 
which iron is encapsulated makes MWCNTs less sus-
ceptible for acid treatment.  
The result obtained shows the differences between 
the removal of iron from MWCNTs and CNOs. This 
fact proves that before carrying out the analysis of any 
others carbon-based nanomaterials, protocols of sample 
pretreatment should be carefully studied as the first 
step. 
 
4. CONCLUSIONS 
 
In this paper we proved that the sample pretreat-
ment protocol is crucial step in analysis. We present 
that different leaching media, used to remove iron, lead 
to different results. The differences in structure of the 
MWCNTs and CNOs have also an impact to the iron 
removal. Moreover, the obtained results could be useful 
in the development of method for CNOs purification or 
direct fast and simple analytical method for determina-
tion of metal content in such nanomaterials. 
 
 
REFERENCES 
 
1. T. Braun, H. Rausch, L.P. Bíró, Z. Konya, I. Kiricsi, J. 
Radioanal. Nucl. Chem. 262, 31 (2004). 
2. P. Mello, L.F. Rodrigues, M.G. Nunes, J.C.P. Mattos,. J. 
Braz. Chem. Soc. 22, 1040 (2011). 
3. A.G. Nasibulin, A. Moisala, D.P. Brown, E.I. Kauppinen, 
Carbon 41, 2711 (2003). 
4. B. Adhikari, B. Muthuraman, C. Mathioudakis, M. Fyta, 
Phys. Status Solidi A 211, 277 (2014). 
5. E. Bekyarova, Y. Ni, E.B. Malarkey, V. Montana, 
J.L. McWilliams, R.C. Haddon, et al., J. Biomed. 
Nanotechnol. 1, 3 (2005). 
6. N. Kuźnik, M.M. Tomczyk, S. Boncel, A.P. Herman, 
K.K.K. Koziol, M. Kempka, Mater. Lett. 136, 34 (2014). 
7. C. Ge, F. Lao, W. Li, Y. Li, C. Chen, Y. Qiu, et al., Anal. 
Chem. 80, 9426 (2008). 
8. S. Porro, S. Musso, M. Vinante, L. Vanzetti, M. Anderle, 
F. Trotta, et al., Physica E 37, 58 (2007). 
9. T. Kolodiazhnyi, M. Pumera, Small 4, 1476 (2008). 
10. S. Boncel, K.K.K. Koziol, Appl. Surf. Sci. 301, 2 (2014). 
11. B. Xu, New Carbon Mater. 23, 289 (2008). 
12. Y. Yang, X. Liu, B. Xu, J. Mater. Res. 23, 1393 (2011).  
13. S. Boncel, Mater. Lett. 65, 2299 (2011). 
 


English

Differences in Iron Removal from Carbon Nanoonions and Multiwall Carbon Nanotubes for Analytical Purpose

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 4 No 2, 02CBNM03(3pp) (2015)   2304-1862/2015/4(2)02CBNM03(3) 02CBNM03-1  2015 Sumy State University Differences in Iron Removal from Carbon Nanoonions and Multiwall  Carbon Nanotubes for Analytical Purpose  J. Bok-Badura1*, A. Jakóbik-Kolon1, M. Turek1, S. Boncel1, K. Karoń1, J. Laskowski2, P. Ceglarski2  1 Faculty of Chemistry, Silesian University of Technology, B. Krzywoustego 6, 44-100 Gliwice, Poland 2 Winiplast, Laboratory of Nanotechnology, Wiosny Ludów 28a, 43-180 Orzesze, Poland   (Received 01 June 2015; published online 24 August 2015)  The paper describes the differences between wet iron removal from carbon nanoonions and from mul-tiwall carbon nanotubes for analytical purpose. Nowadays, both carbon nanoonions and multiwall carbon nanotubes are one of the most interesting materials with applicability in electronics, medicine and bio-technology. Medical applications of those nanomaterials require not only recognition of their structure but also measurement of metal impurities concentration. Inductively coupled plasma optical emission spec-trometry as a method for Fe-determination requires liquid samples. Hence, we propose various protocols for leaching of iron from studied materials. Our results proved that structure of nanomaterials have an impact on the efficiency of iron removal.  Keywords: Multiwall carbon nanotubes, Carbon nanoonions, Iron, ICP-OES.   PACS numbers: 81.07.De, 81.05.Tp, 81.70.Jb                                                             * Joanna.Bok-Badura@polsl.pl   1. INTRODUCTION  Multiwall carbon nanotubes (MWCNTs) since their discovery have been one of the most interesting mate-rials in science. This is due to their unique properties (chemical, mechanical, magnetic and electronic) [1–3]. Another interesting material which exhibits similar to MWCNTs properties are carbon nanoonions (CNOs). Both MWCNTs and CNOs can be used in optics and electronics but also in biotechnology and medicine [4,5]. Synthesis of CNTs and CNOs often requires metal catalyst (e.g. Fe, Mo, Co, Ni and others) which usually remain in the products as impurities. But also, some elements are deliberately introduced into the nano-materials structure in order to add to them special properties [6]. The presence of metal nanoparticles in CNTs and CNOs – both as contaminants and modifiers – should be conveniently monitored, especially as for medical application.  There were a few methods already proposed for iron content determination in MWCNTs: instrumental neu-tron activation analysis (INAA) [1], inductively coupled plasma mass spectrometry (ICP-MS) [7], thermogravi-metric analysis (TGA) [8,9], X-ray photoelectron spec-troscopy (XPS) [9], scanning electron microsco-py/energy-dispersive X-ray spectrometry (SEM/EDX) [8,9], transmission electron microscopy/ energy-dispersive X-ray spectrometry (TEM/EDX) [9], induc-tively coupled plasma optical emission spectrometry ICP-OES [10] whereas for CNOs only three: TEM, XRD and TGA [11,12]. Most of these methods are only quali-tative or semi-quantitative and they do not provide information about concentration or the results are only estimated. In methods such as ICP-OES or ICP-MS, which could give full information on particular ele-ments concentration, liquid samples are required. However, because of the extreme difficulties in destruc-tion of carbon nanomaterials structure – procedures of sample pretreatment constitute the most obstacle step in such analysis. Dry ashing coupled with acid extrac-tion, wet digestion, combination of dry ashing with acid digestion and microwave-assisted digestion as a MWCNTs sample pretreatment protocol for ICP-MS were already proposed [7]. These methods are time-consuming, laborious, and multistage. They also re-quire the use of aggressive chemicals and conditions and depend on the type and structure of materials. In addition, they not always ensure complete extraction of the interesting element. This behavior can cause some mistakes in the further analysis. A use of MWCNTs or CNOs certified reference materials would be the most appropriate procedure to estimate the efficiency of iron removal. Unfortunately, such materials have not been yet available since a huge variety of molecular archi-tectures of these carbon nanostructures were synthe-sized under a range of different conditions. In this paper we propose a method of removing iron from the CNOs as an sample pretreatment protocol for the ICP-OES analysis. In addition, the same experi-ments were conducted for MWCNTs to present similar-ities and differences in the behavior of these materials under different conditions.   2. EXPERIMENTAL   2.1 Materials and reagents  MWCNTs and CNOs were synthesized via catalytic chemical vapor deposition (c-CVD). MWCNTs were obtained according to a procedure previously described, briefly at 760 °C using FeCp2 as iron precursor, toluene as carbon source and Ar as carrier gas [13]. In turn, CNOs were obtained from hydrogen pre-treated iron oxides nanoparticles as catalyst, acetylene as carbon source and Ar as carrier gas (800 °C). To remove iron from examined material nitric acid (65%, Suprapur, Merck), sulfuric acid (98%, Suprapur, Merck) were used. For calibration stock standard solu-tions of Fe (1mg mL-1 in 2% HNO3, CPI International)  J. BOK-BADURA, A. JAKÓBIK-KOLON ET AL. PROC. NAP 4, 02CBNM03 (2015)   02CBNM03-2 was used. All solution and samples were prepared with using ultrapure water (MilliporeElix 10 System).  2.2 Instrumentation  Scanning electron microscope (Phenom Pro Desktop SEM) was used to obtain the micrographs of MWCNTs and CNOs.  All determination of Fe concentrations were per-formed utilizing Varian 710-ES spectrometer equipped with an OneNeb nebulizer (Varian, Australia). Operat-ing parameters are described in Table 1.   Table 1 – The operating parameters of ICP-OES analysis   RF power, kW 1 Ar plasma flow rate, L min-1 15 Ar carrier flow rate, L min-1 1.5 Nebulizer pressure, kPa 210 Pump rate, rpm 15 Viewing axial Fe wavelength, nm 234.350, 261.187, 261.382  2.3 Sample pretratment   Five different conditions were chosen to examine the extractability of iron from CNOs and MWCNTs: water, diluted HNO3, concentrated HNO3, mixture of concentrated HNO3 and H2SO4 (4:1) and microwave digestion (MARS 5 CEM Corp. 200°C, ramp time 15 min., hold time 15 min.) in mixture of  concentrated HNO3 and H2SO4 (4:1). All the samples, with the excep-tion of samples for mineralization, were shaken with the solution for 12 hours at room temperature using the laboratory shaker. After that samples were filtered and the obtained solutions were analyzed using ICP-OES.  3. RESULTS AND DISCUSION   3.1 Structure  Firstly, SEM micrographs of examined materials were prepared to compare their structures (see Fig. 1).    Fig. 1 – SEM image (a), MWCNTs with encapsulated Fe catalyst (b), CNOs with encapsulated Fe catalyst  The differences in structure of carbon nanotubes and carbon nanoonions  are clearly visible. CNOs have a spherical shape with smooth surface in contract to the MWCNTs that have the needle-like fiber shape. This difference was also visible in product of minerali-zation. CNOs after mineralization get slurry of small particles evenly dispersed in a solution whereas MWCNTs gets a slurry of puffed up bundles of a signif-icantly greater volume (see. Fig. 2).    Fig. 2 – Slurries after mineralization (a), CNOs (b), MWCNTs   3.2 Determination of iron content in leachate by ICP-OES analysis  Iron content in studied CNOs and MWCNTs ob-tained after leaching with nitric and sulfuric acid in a few conditions are presented in Fig. 3a and 3b. Results obtained from water solution were omitted because iron wasn’t being removed under these conditions.     Fig. 3 – Iron concentration (ICP-OES) in (a), CNOs (b), MWCNTs obtained after using different sample pretreatment: A – 5% HNO3, B – conc. HNO3, C – mixture of conc. HNO3 and conc. H2SO4 (4:1), D - mixture of conc. HNO3 and conc. H2SO4 (4:1) and mineralization  The best results for CNOs and MWCNTs were measured if diluted nitric acid and microwave  mineral-ization in mixture of  concentrated nitric and sulfuric a b a b  DIFFERENCES IN REMOVAL IRON CONTENT FROM CARBON NANOONIONS … PROC. NAP 4, 02CBNM03 (2015)   02CBNM03-3 acid were used respectively. When concentrated nitric acid was used the obtained results were about half lower than when diluted acid was used. It could be due to the fact that in concentrated acid iron is rendered passive. If 5% HNO3 and mineralization in conc. HNO3 and H2SO4 were used the highest content of iron was removed from CNOs (there is only a 12% difference). Otherwise, in the case of MWCNTs difference in ob-tained results, in mentioned condition, was about 40%. This fact may be related to differences in the structure of the CNOs and the MWCNTs. Fiber like structure in which iron is encapsulated makes MWCNTs less sus-ceptible for acid treatment.  The result obtained shows the differences between the removal of iron from MWCNTs and CNOs. This fact proves that before carrying out the analysis of any others carbon-based nanomaterials, protocols of sample pretreatment should be carefully studied as the first step.  4. CONCLUSIONS  In this paper we proved that the sample pretreat-ment protocol is crucial step in analysis. We present that different leaching media, used to remove iron, lead to different results. The differences in structure of the MWCNTs and CNOs have also an impact to the iron removal. Moreover, the obtained results could be useful in the development of method for CNOs purification or direct fast and simple analytical method for determina-tion of metal content in such nanomaterials.   REFERENCES  1. T. Braun, H. Rausch, L.P. Bíró, Z. Konya, I. Kiricsi, J. Radioanal. Nucl. Chem. 262, 31 (2004). 2. P. Mello, L.F. Rodrigues, M.G. Nunes, J.C.P. Mattos,. J. Braz. Chem. Soc. 22, 1040 (2011). 3. A.G. Nasibulin, A. Moisala, D.P. Brown, E.I. Kauppinen, Carbon 41, 2711 (2003). 4. B. Adhikari, B. Muthuraman, C. Mathioudakis, M. Fyta, Phys. Status Solidi A 211, 277 (2014). 5. E. Bekyarova, Y. Ni, E.B. Malarkey, V. Montana, J.L. McWilliams, R.C. Haddon, et al., J. Biomed. Nanotechnol. 1, 3 (2005). 6. N. Kuźnik, M.M. Tomczyk, S. Boncel, A.P. Herman, K.K.K. Koziol, M. Kempka, Mater. Lett. 136, 34 (2014). 7. C. Ge, F. Lao, W. Li, Y. Li, C. Chen, Y. Qiu, et al., Anal. Chem. 80, 9426 (2008). 8. S. Porro, S. Musso, M. Vinante, L. Vanzetti, M. Anderle, F. Trotta, et al., Physica E 37, 58 (2007). 9. T. Kolodiazhnyi, M. Pumera, Small 4, 1476 (2008). 10. S. Boncel, K.K.K. Koziol, Appl. Surf. Sci. 301, 2 (2014). 11. B. Xu, New Carbon Mater. 23, 289 (2008). 12. Y. Yang, X. Liu, B. Xu, J. Mater. Res. 23, 1393 (2011).  13. S. Boncel, Mater. Lett. 65, 2299 (2011).  

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Differences in Iron Removal from Carbon Nanoonions and Multiwall Carbon Nanotubes for Analytical Purpose

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