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On the production of higher fullerenes with doped electrodes
ELSEVIER
SyntheticMetals77 (1996) 213-215
On the production of higher fullerenes with doped electrodes T. Almeida Murphy a, S. Carl a, C. Wolf a,B. Mertesacker a, A. Weidinger a,A. Lehmann b b Bundesanstaltfiir
’ Hahn-Meitner-lnstitut Materialforschung,
Berlin GmbH, Glienicker Strasse 100, D-14109 Berlin, Germany Lab. 10.22, Massenspektroskopie, Rudower Chaussee 5, D-12489
Berlin,
Germany
Abstract We have studied in which way the doping of graphite electrodesin the arc discharge production of fullerenes affectsthe yields of higher fullerenes. In some casesvery high yields were observed,but the reproducibility waspoor. The higher fullerenes CY6,C2,,-CT8and O&8 were enriched by a one-step high-pressure liquid chromatography. After the enrichment we studied the stability of these fullerenes in the presenceof oxygen. The isomer C2V-C,sdisappearedafter some days in solution or whentreated with oxygen. Keywords:
Fullerene;Doping; Electrodes
1. Experimental
results and discussion
We have shown previously [l] that the yield of higher fullerenes (C,, n 2 76) can be significantly increased using graphite rods doped with hafnium carbide (HfC) in the arc discharge production of fullerenes. In these experiments graphite tubes of 9 mm outer diameter and 6 mm inner diameter were filled with pellets with the composition 40 wt.% HfC, 35 wt.% graphite powder and 25 wt.% pitch. The pellets were pressed with 2 kbar pressure and sintered in vacuum at a temperature of 900 “C. A mass spectrum of a sample produced in this way (toluene soot extract) is shown in Fig. 1.
It can be seen that, contrary to the usual case, the Cs4 peak is the highest and also the other higher fullerenes have high intensities. In the meantime, we have continued these experiments with the intention to optimize the yield of higher fullerenes. Among other things we varied the HfC content of the electrodes, the helium pressure and the current used for the arc discharge. We have not been able to find a definite relationship between these parameters and the yield of higher fullerenes. We presume that special conditions in the arc discharge play an important role in how much and which fullerenes are produced. The arc discharge conditions of our actual exper-
’
E+05 4.23
c70 -l
-78
I
C7G
750
800
850 m/Z
900
950
1000
Fig. 1.FAB negativemassspectrumof the toluenesootextract,whichwasproducedwithgraphiterodsdopedwithhafniumcarbide. 0379-6779/96/$15.000 1996ElsevierScienceS.A.All rightsreserved
214
T. Almeida
Murphy
et al. /Synthetic
Metals
77 (1996)
213-21.5
Table 1 Relative area of the peaks from chromatograms taken from samples, which were produced with PAH-doped electrodes. The absolute yields are related to the soot weights. Chromatographic conditions: eluent: CH,ClJCHsOH 56144 (vol./vol.), column: Spherisorb, 240 X4 mm, 5 pm, eluent rate: 1 ml/mm, A=240 nm PAH
GQO (%I
Gil (“ro)
c70
Naphthalene Anthracene Acenaphthene Chrysene
1.68 2.10 3.97
55.22 40.00
35.19 38.96
6.87 17.90
3.30 6.75
53.50 51.70
37.40 36.50
2.32
4.70 4.35
2.00
imental set-up are difficult to control and therefore no systematic studies in this direction were possible. In further experiments we have systematically doped the graphite electrodes with polycyclic aromatic hydrocarbons (PAHs) , which contain five-membered and six-membered carbon rings. We filled the electrodes with a mixture of graphite powder, pitch and the PAH naphthalene, anthracene, acenaphthene and chrysene in different proportions. Table 1 shows the relative areas of the peaks from high-pressure liquid chromatography (HPLC) chromatograms taken from probes, which were produced with PAH-doped electrodes. In some cases we were able to improve the yield of higher fullerenes, but altogether we did not find a higher production rate. The absolute yield of fullerenes is even smaller than using undoped electrodes. This fact can be explained assuming that the hydrogen containedin the PAH inhibits the nucleation of the fullerenes [ 2,3]. We also studied the stability of the fullerenes CT6, C2v-C,s and D,-C,s. The chromatographic conditions for the separation of these fullerenes are well known and have been published in earlier works [4-6], We performed the isolation of an enriched sample of these fullerenes using a one-step HPLC separation set-up. In this case the crude extract (see Fig. 2) was separated chromatographically into the fractions &a, C,,, and the higher fullerenes using two HPLC columns (Eurospher 100 Cis reversed phase, 7 km, 250X40 mm) connected in series in order to enhance the separation of the higher fullerenes. The eluent used for the separation consisted of a mixture of 55:45 (vol./vol.) toluene-acetonitrile. In this mixture the higher fullerenes can be easily separated in their retention times. The UV detector was set at 290 nm. A first run using a flow rate of 50 ml/min led to the yellowish enriched fraction shown by the HPLC chromatogram in Fig. 3(a). Here we see a minor C,,, peak and the higher fullerenes C76, C20-C78and Ds-C7s, After leaving this fraction in solution for 5 days in the dark we observed a decay of C,,CY8and two new peaks between C,,, and CT6at the retention times 15.45 and 16.05 min, and another new peak below C,e at the retention time 11.4 1 min. This can be seen in Fig. 3 (b) . The new peaks are indicated with arrows. Part of the enriched fraction was dried under a nitrogen stream, afterwards treated with oxygen (35 ml/min) for 19 h and finally dissolved in toluene. A HPLC chromatogram of this solution is shown in Fig. 3 (c) . This HPLC chromatogram shows the same result
CC, (nz76)
(%a)
(%)
Abs. yield (%)
6.94
as seen in Fig. 3 (b), where the absence of the C2&s fullerene peak can be observed. These results show that the higher fullerenes we studied are sensitive to the exposure to air and oxygen in solution as well as a solid. This means that a careful handling of these fullerenes is necessary, in particular the contact with oxygen should be avoided.
Timelmin Fig. 2. HPLC chromatogram from the crude extract of a fullerene probe producedusingagraphiterod doped withhafniumcarbide.Thiscntdeextract was used for the one-step HPLC separation, For chromatographic conditions, see Table 1,
111
0
a
4
8
12
16
20
24
Timelmin Fig. 3. HPLC chromatograms of the higher fullerenes after one-step chromatographic separation (a), after 5 days in the dark in solution (b), after 19 h being treated with oxygen as a dried powder (c), The new peaks are indicated by arrows. For chromatographic conditions, see the text.
T. Almeida
Murphy
et al. /Synthetic
The three new peaks that appear after the decay of the higher fullerenes are presumably the corresponding oxides of C70, C76 and &. This is currently being examined by mass spectroscopy and liquid chromatography mass spectroscopy (LC-MS).
Metals
Fullerene Properties
[2] [‘3] [4]
References
[5]
[I] G. Aced, T. Almeida Murphy, J. Erxmeyer, B. Mertesacker, H.J. Mb;ckel, D. Nagengast, B. Pietzak, C. Rau and A. Weidinger, in H. Kuzmany, J. Fink, M. Mehring and S. Roth (eds.), Progress in
[6]
215
77 (1996) 213-215 Research, International ofNovel Materials, World
Winterschool
on
Electronic
Scientific, Singapore, 1994, p. 14. M. Broyer, A. Goeres, M. Pellarin, E. Sedlmayr, J.L. Vialle and L. WGste, Chem. Phys. Lett., 198 (1992) 128. C.J. Pope, J.A. Man- and J.B. Howard, J. Phys. Chem., 97 (1993) 11001. F. Diederich, R. Ettl, Y. Rubin, R.L. Whetten, R. Beck, M. Alvarez, S. Anz, D. Sensharma,F. Wudl, K.C. Khemani and A. Koch, Science, 252 (1991) 548. K. Kikuchi, N. Nakahara, T. Wakabayashi, M. Honda, H. Matsumiya, T. Moriwaki, S. Suzuki, H. Shiromaru, K. Saito, K. Yamauchi, I. Ikemoto and Y. Achiba, Chem. Phys. Left., I88 (1992) 177. F. Diederich, R.L. Whetten, C. Thilgen, R. Ettl, I. Chao and M.M. Alvarez, Science, 254 (1991) 1768.
SyntheticMetals77 (1996) 213-215
On the production of higher fullerenes with doped electrodes T. Almeida Murphy a, S. Carl a, C. Wolf a,B. Mertesacker a, A. Weidinger a,A. Lehmann b b Bundesanstaltfiir
’ Hahn-Meitner-lnstitut Materialforschung,
Berlin GmbH, Glienicker Strasse 100, D-14109 Berlin, Germany Lab. 10.22, Massenspektroskopie, Rudower Chaussee 5, D-12489
Berlin,
Germany
Abstract We have studied in which way the doping of graphite electrodesin the arc discharge production of fullerenes affectsthe yields of higher fullerenes. In some casesvery high yields were observed,but the reproducibility waspoor. The higher fullerenes CY6,C2,,-CT8and O&8 were enriched by a one-step high-pressure liquid chromatography. After the enrichment we studied the stability of these fullerenes in the presenceof oxygen. The isomer C2V-C,sdisappearedafter some days in solution or whentreated with oxygen. Keywords:
Fullerene;Doping; Electrodes
1. Experimental
results and discussion
We have shown previously [l] that the yield of higher fullerenes (C,, n 2 76) can be significantly increased using graphite rods doped with hafnium carbide (HfC) in the arc discharge production of fullerenes. In these experiments graphite tubes of 9 mm outer diameter and 6 mm inner diameter were filled with pellets with the composition 40 wt.% HfC, 35 wt.% graphite powder and 25 wt.% pitch. The pellets were pressed with 2 kbar pressure and sintered in vacuum at a temperature of 900 “C. A mass spectrum of a sample produced in this way (toluene soot extract) is shown in Fig. 1.
It can be seen that, contrary to the usual case, the Cs4 peak is the highest and also the other higher fullerenes have high intensities. In the meantime, we have continued these experiments with the intention to optimize the yield of higher fullerenes. Among other things we varied the HfC content of the electrodes, the helium pressure and the current used for the arc discharge. We have not been able to find a definite relationship between these parameters and the yield of higher fullerenes. We presume that special conditions in the arc discharge play an important role in how much and which fullerenes are produced. The arc discharge conditions of our actual exper-
’
E+05 4.23
c70 -l
-78
I
C7G
750
800
850 m/Z
900
950
1000
Fig. 1.FAB negativemassspectrumof the toluenesootextract,whichwasproducedwithgraphiterodsdopedwithhafniumcarbide. 0379-6779/96/$15.000 1996ElsevierScienceS.A.All rightsreserved
214
T. Almeida
Murphy
et al. /Synthetic
Metals
77 (1996)
213-21.5
Table 1 Relative area of the peaks from chromatograms taken from samples, which were produced with PAH-doped electrodes. The absolute yields are related to the soot weights. Chromatographic conditions: eluent: CH,ClJCHsOH 56144 (vol./vol.), column: Spherisorb, 240 X4 mm, 5 pm, eluent rate: 1 ml/mm, A=240 nm PAH
GQO (%I
Gil (“ro)
c70
Naphthalene Anthracene Acenaphthene Chrysene
1.68 2.10 3.97
55.22 40.00
35.19 38.96
6.87 17.90
3.30 6.75
53.50 51.70
37.40 36.50
2.32
4.70 4.35
2.00
imental set-up are difficult to control and therefore no systematic studies in this direction were possible. In further experiments we have systematically doped the graphite electrodes with polycyclic aromatic hydrocarbons (PAHs) , which contain five-membered and six-membered carbon rings. We filled the electrodes with a mixture of graphite powder, pitch and the PAH naphthalene, anthracene, acenaphthene and chrysene in different proportions. Table 1 shows the relative areas of the peaks from high-pressure liquid chromatography (HPLC) chromatograms taken from probes, which were produced with PAH-doped electrodes. In some cases we were able to improve the yield of higher fullerenes, but altogether we did not find a higher production rate. The absolute yield of fullerenes is even smaller than using undoped electrodes. This fact can be explained assuming that the hydrogen containedin the PAH inhibits the nucleation of the fullerenes [ 2,3]. We also studied the stability of the fullerenes CT6, C2v-C,s and D,-C,s. The chromatographic conditions for the separation of these fullerenes are well known and have been published in earlier works [4-6], We performed the isolation of an enriched sample of these fullerenes using a one-step HPLC separation set-up. In this case the crude extract (see Fig. 2) was separated chromatographically into the fractions &a, C,,, and the higher fullerenes using two HPLC columns (Eurospher 100 Cis reversed phase, 7 km, 250X40 mm) connected in series in order to enhance the separation of the higher fullerenes. The eluent used for the separation consisted of a mixture of 55:45 (vol./vol.) toluene-acetonitrile. In this mixture the higher fullerenes can be easily separated in their retention times. The UV detector was set at 290 nm. A first run using a flow rate of 50 ml/min led to the yellowish enriched fraction shown by the HPLC chromatogram in Fig. 3(a). Here we see a minor C,,, peak and the higher fullerenes C76, C20-C78and Ds-C7s, After leaving this fraction in solution for 5 days in the dark we observed a decay of C,,CY8and two new peaks between C,,, and CT6at the retention times 15.45 and 16.05 min, and another new peak below C,e at the retention time 11.4 1 min. This can be seen in Fig. 3 (b) . The new peaks are indicated with arrows. Part of the enriched fraction was dried under a nitrogen stream, afterwards treated with oxygen (35 ml/min) for 19 h and finally dissolved in toluene. A HPLC chromatogram of this solution is shown in Fig. 3 (c) . This HPLC chromatogram shows the same result
CC, (nz76)
(%a)
(%)
Abs. yield (%)
6.94
as seen in Fig. 3 (b), where the absence of the C2&s fullerene peak can be observed. These results show that the higher fullerenes we studied are sensitive to the exposure to air and oxygen in solution as well as a solid. This means that a careful handling of these fullerenes is necessary, in particular the contact with oxygen should be avoided.
Timelmin Fig. 2. HPLC chromatogram from the crude extract of a fullerene probe producedusingagraphiterod doped withhafniumcarbide.Thiscntdeextract was used for the one-step HPLC separation, For chromatographic conditions, see Table 1,
111
0
a
4
8
12
16
20
24
Timelmin Fig. 3. HPLC chromatograms of the higher fullerenes after one-step chromatographic separation (a), after 5 days in the dark in solution (b), after 19 h being treated with oxygen as a dried powder (c), The new peaks are indicated by arrows. For chromatographic conditions, see the text.
T. Almeida
Murphy
et al. /Synthetic
The three new peaks that appear after the decay of the higher fullerenes are presumably the corresponding oxides of C70, C76 and &. This is currently being examined by mass spectroscopy and liquid chromatography mass spectroscopy (LC-MS).
Metals
Fullerene Properties
[2] [‘3] [4]
References
[5]
[I] G. Aced, T. Almeida Murphy, J. Erxmeyer, B. Mertesacker, H.J. Mb;ckel, D. Nagengast, B. Pietzak, C. Rau and A. Weidinger, in H. Kuzmany, J. Fink, M. Mehring and S. Roth (eds.), Progress in
[6]
215
77 (1996) 213-215 Research, International ofNovel Materials, World
Winterschool
on
Electronic
Scientific, Singapore, 1994, p. 14. M. Broyer, A. Goeres, M. Pellarin, E. Sedlmayr, J.L. Vialle and L. WGste, Chem. Phys. Lett., 198 (1992) 128. C.J. Pope, J.A. Man- and J.B. Howard, J. Phys. Chem., 97 (1993) 11001. F. Diederich, R. Ettl, Y. Rubin, R.L. Whetten, R. Beck, M. Alvarez, S. Anz, D. Sensharma,F. Wudl, K.C. Khemani and A. Koch, Science, 252 (1991) 548. K. Kikuchi, N. Nakahara, T. Wakabayashi, M. Honda, H. Matsumiya, T. Moriwaki, S. Suzuki, H. Shiromaru, K. Saito, K. Yamauchi, I. Ikemoto and Y. Achiba, Chem. Phys. Left., I88 (1992) 177. F. Diederich, R.L. Whetten, C. Thilgen, R. Ettl, I. Chao and M.M. Alvarez, Science, 254 (1991) 1768.