Reductive addition reactions of single-walled carbon nanotubes representing a wide diameter range were applied and investigated by Raman spectroscopy, thermogravimetry-mass spectrometry, 1H-NMR spectrometry and wide range optical spectroscopy.
To compare efficiency, diameter and other selectivity and reactivity of the nanotu-bes, two different reaction mechanisms and functional groups (modified Birch reduc-tion and alkali metal intercalareduc-tion; H and n-Bu) were used. The main difference in the applied mechanisms is that modified Birch reduction is a quasi-homogeneous, solution-phased reaction, while alkali metal intercalation followed by addition of electrophilic reagents is a solid-phase reaction. In the case of modified Birch reduction, the real reactants are the more or less individual nanotubide anions, in the case of alkali metal intercalation, the intercalated nanotube bundles.
At the n-butylation reaction of HiPco nanotubes, hydrogenation as a side reaction was expected. On the contrary, at both mechanism, hydrogenated nanotubes were the main products, and n-butylation seemed to be the side reaction. This lets us conclude that hydrogenation is far more fast and/or favorable than n-butylation.
The degree of functionalization could be increased in all reactions by successive steps. This can be explained by the bundling of the nanotubes. Even in the case of modified Birch reduction we cannot speak about a homogeneous reaction with individ-ually dispersed nanotubes, albeit the size of the bundles is much smaller and they are much loosened due to the repulsion of the negatively charged nanotubes, and due to the possibility for these smaller bundles to repel from each other in the liquid phase.
Alkali metal intercalation followed by addition of electrophilic reagents is a solid-phase reaction, and even when toluene is added as a ”medium” for the reaction, it remains a solid-phase one, since the negatively charged nanotube bundles with alkali metal cations in their interstitial channels (or on their surfaces) will not be dispersed in the apolar toluene.
As proven by optical spectroscopy, the diameter selectivity of hydrogenation by using two different reaction mechanisms is different. The difference is explained by the tendency of nanotubes towards bundling. Since bundling can limit the accessibility of the individual tubes inside, this effect also must be taken into account besides the simple increasing diameter-decreasing reactivity considerations.
Anyhow, by applying successive steps, each step seems to increase the loosening of the bundles making new, formerly intact tubes available for the reactants, proven by the increasing degree of functionalization in each case.
Investigating further the hydrogenation by alkali metal intercalation by using differ-ent starting SWNT, with three differdiffer-ent ratios of ionic radii of alkali metal cations and mean diameters of nanotubes, three different diameter selectivities could be detected.
It was demonstrated that the selectivity of this type of reductive hydrogenation is very sensitive to energetics of the competing processes. With these three starting nanotubes all the possible cases could be represented.
Acknowledgement
First of all, I would like to thank my supervisor, Katalin Kamar´as for supporting me and assuming the guidance of my PhD work. She showed great patience to me all the time from my first steps. She involved me in lots of projects and collaborations, which I found really great and interesting. I am also grateful for the useful and important scientific and social skills I learnt from her.
I am truly grateful to S´andor Pekker for his extensive help with my work, and for the inspiring discussions.
I am also grateful to ´Eva Kov´ats and Ferenc Borondics for their useful advice and help with the laboratory work.
I would like to thank Emma Jakab for the essential thermogravimetry-mass spec-trometric measurements on my samples.
Warm thanks are due to ´Aron Pekker, P´eter Nemes-Incze and Hajnalka M´aria T´oh´ati for their help with the transmission spectroscopic and AFM measurements.
I thank M´onika Bokor, Tam´as Vereb´elyi and K´alm´an Tompa for the NMR mea-surements on my samples, and for the useful discussions.
Thanks to all my colleagues: Bea Botka, B´alint Korbuly, ´Eva Kov´ats, P´eter Matus, Aron Pekker, Gy¨´ ongyi Pergern´e Klupp, L´aszl´o R´atkai, Zsolt Szekr´enyes and Hajnalka M´aria T´oh´ati for creating a friendly, cheerful and supporting milieu in the lab and in the office. The amount of chocolate and coffee had together speaks for itself.
I am grateful to L´aszl´o Kov´acs and Mikl´os Veres for allowing me to use the UV-Vis and Raman spectrometers, respectively.
I am grateful to the Institute for Solid State Physics and Optics, Wigner Research Centre for Physics for the opportunity to work among its walls.
Last but not least, I am truly grateful to my family and friends for their love, support and encouragement all along the years. Special thanks are concerned to my husband, L´aszl´o for his mental support, for the solid background of which this work would not have been possible without and for his incontestable care and love.
Theses
1. I synthesized hydrogenated HiPco nanotubes in three successive steps by modi-fied Birch reduction and potassium intercalation followed by addition of methanol.
According to thermogravimetry-mass spectrometric measurements, the H-content was 2-4 H/100 C in both cases. However, I detected by optical spectroscopy that the diameter selectivity of these reactions was different: in the case of modified Birch reduction the smaller diameter tubes, in the case of potassium intercalation the larger diameter tubes were more reactive. I explained this discrepancy by the different reaction mechanisms: at modified Birch reduction the individual nano-tubes, at potassium intercalation the nanotube bundles are the primer reactants.
In the latter case, the determinative factor is the accessibility of the individual nanotubes inside the bundles. The incorporation of potassium cations is easier into bundles of larger diameter tubes.
2. I prepared hydrogenated and n-butylated HiPco single-walled carbon nanotubes in three successive steps by both modified Birch reduction and potassium inter-calation. According to thermogravimetry-mass spectrometry measurements the n-butyl content of the samples was ∼1 n-Bu/100 C, the hydrogen content was 2-3 H/100 C in spite of lack of addition of methanol to the system. I explained this anomaly by the presence of other protic H sources (water, oxide, hydroxide) and that the hydrogenation can be faster and/or favorable than n-butylation.
3. I investigated the diameter selectivity of hydrogenation by alkali metal intercala-tion on single-walled carbon nanotubes by using three different mean diameters and diameter distributions (P2, HiPco, CoMoCat) and two alkali metals with different ionic radii (K, Rb) on a wide diameter range and at three different ionic radius/nanotube diameter ratios. Thermogravimetry-mass spectrometric and 1
H-NMR results revealed that the degree of hydrogenation is 2-4 H/100 C in the case of small (K/P2) and medium (K/HiPco) ratios, and at around 1 H/100 C at large (Rb/CoMoCat) ratio.
4. I investigated the diameter selectivity of hydrogenation of single-walled carbon nanotubes by alkali metal intercalation followed by addition of methanol on a wide diameter range. By optical spectroscopy I detected no selectivity at small ionic radius/nanotube diameter ratio, reversed selectivity at medium ratio and normal selectivity at large ratio. I explained these results by the activation energy of alkali metal intercalation into nanotube bundles, which depends on nanotube diameter and ionic radii.
5. I prepared hydrogenated and n-butylated HiPco single-walled carbon nanotubes by modified Birch reduction and potassium intercalation in three successive steps, respectively. It was demonstrated by thermogravimetry-mass spectrometry that the degree of functionalization could be increased at both types of reactions by applying successive steps. I explained this by the step-by-step loosening of the nanotube bundles. This even affects in the homogeneous phase modified Birch reduction.
T´ ezispontok
1. Hidrog´enezett
HiPco nanocs¨oveket ´all´ıtottam el˝o h´arom l´ep´esben m´odos´ıtott Birch-redukci´oval
´
es k´alium interkal´aci´oval. Termogravimetria-t¨omegspektometriai m´er´esek szerint a H-tartalom 2-4 H/100 C-nek ad´odott mindk´et reakci´o eset´en. Optikai spek-troszk´opia seg´ıts´eg´evel azonban kimutattam, hogy az ´atm´er˝o-szelektivit´as k¨ul¨ on-b¨oz˝o: m´odos´ıtott Birch-redukci´o eset´en a kisebb ´atm´er˝oj˝u cs¨ovek, a k´alium in-terkal´aci´o eset´en a nagyobb ´atm´er˝oj˝uek bizonyultak reakt´ıvabbaknak. Az elt´er´est a k¨ul¨onb¨oz˝o reakci´o-mechanizmussal magyar´aztam: m´odos´ıtott Birch-redukci´o es-et´en az egyedi nanocs¨ovek reaktivit´asa a d¨ont˝o, k´alium interkal´aci´on´al az egyedi nanocs¨ovek hozz´af´erhet˝os´ege a k¨otegeken bel¨ul a be´ep¨ul˝o K-ionok sz´am´ara. A K-ionok be´ep¨ul´ese k¨onnyebb a nagyobb ´atm´er˝oj˝u cs¨ovek k¨otegeibe.
2. Hidrog´enezett ´es n-butilozott HiPco nanocs¨oveket ´all´ıtottam el˝o h´arom l´ep´ es-ben m´odos´ıtott Birch-redukci´oval ´es k´alium interkal´aci´oval. Termogravimetria-t¨omegspektrometriai m´er´esek szerint a mint´akban ∼1 n-Bu/100 C n-butil-tartalom, ´es 2-3 H/100 C hidrog´en volt annak ellen´ere, hogy hidrog´enez˝o szert nem adtam a rendszerhez. Ezt azzal magyar´aztam, hogy a hidrog´enez˝od´est a je-lenl´ev˝o protikus H-tartalm´u szennyez˝ok okozz´ak (v´ız, oxidok, hidroxidok), ´es a hidrog´enez˝od´es gyorsabb ´es/vagy kedvezm´enyezettebb lehet, mint a butiloz´as.
3. Alk´alif´em interkal´aci´os hidrog´enez´es kitermel´es´et tanulm´anyoztam egyfal´u sz´en nanocs¨oveken sz´eles ´atm´er˝o-tartom´anyban, h´arom k¨ul¨onb¨oz˝o ´atlagos ´atm´er˝oj˝u nanocs˝o (P2, HiPco, CoMoCat) ´es k´et k¨ul¨onb¨oz˝o ion´atm´er˝oj˝u alk´alif´em (K, Rb) felhaszn´al´as´aval. Termogravimetria-t¨omegspektrometria ´es1H-NMR m´er´esek seg´ıts´eg´evel kimutattam, hogy a hidrog´en-tartalom 2-4 H/100 C kis ´es k¨ozepes
ion´atm´er˝o/nanocs˝o-´atm´er˝o ar´anyon´al (K/P2 ´es K/HiPco), ´es <1 H/100 C nagy ion´atm´er˝o/nanocs˝o-´atm´er˝o ar´anyn´al (Rb/CoMoCat).
4. Alk´alif´em interkal´aci´os hidrog´enez´es ´atm´er˝o-szelektivit´as´at tanulm´anyoztam egy-fal´u sz´en nanocs¨oveken sz´eles ´atm´er˝o-tartom´anyban, h´arom k¨ul¨onb¨oz˝o ´atlagos ´ at-m´er˝oj˝u nanocs˝o (P2, HiPco, CoMoCat) ´es k´et k¨ul¨onb¨oz˝o ion´atm´er˝oj˝u alk´alif´em (K, Rb) felhaszn´al´as´aval. Optikai spektroszk´opia seg´ıts´eg´evel kimutattam, hogy kis ion´atm´er˝o/nanocs˝o-´atm´er˝o ar´anyn´al nem mutathat´o ki ´atm´er˝o-szelektivit´as, k¨ozepes ar´anyn´al a nagyobb ´atm´er˝oj˝u, nagy ar´anyn´al a kis ´atm´er˝oj˝u nanocs¨ o-vek a reakt´ıvabbak. Ezt az interkal´aci´o nanocs˝o- ´es ion´atm´er˝o-f¨ugg˝o aktiv´al´asi energi´aj´aval magyar´aztam.
5. M´odos´ıtott Birch-redukci´oval, illetve k´alium interkal´aci´oval hidrog´enezett, valamint n-butilozott HiPco nanocs¨oveket ´all´ıtottam el˝o. H´arom egym´ast k¨ovet˝o l´ep´esben elv´egezve a reakci´okat, termograviemtria-t¨omegspektromerti´as m´er´esekkel kimutattam, hogy a kitermel´es mindk´et reakci´ot´ıpusn´al ´es mind-k´et funci´os csoportn´al n¨ovelhet˝o egym´ast k¨ovet˝o l´ep´esek alkalmaz´as´aval. Ezt a nanocs˝o-k¨otegek l´ep´esenk´enti fokozatos fellazul´as´aval magyar´aztam, amely sz-erepet j´atszik m´eg a homog´en f´azis´u m´odos´ıtott Birch-redukci´on´al is.
List of publications
Publications related to the thesis:
1. K. N´emeth, ´A. Pekker, F. Borondics, E. Jakab, N. M. Nemes, K. Kamar´as and S. Pekker. Investigation of hydrogenated HiPCo nanotubes by infrared spec-troscopy. Phys. Status Solidi B 247:2855, 2010.
2. K. Nemeth, E. Jakab, F. Borondics, H. M. T´oh´ati, ´A. Pekker, M. Bokor, T. Vere-b´elyi, K. Tompa, S. Pekker and K. Kamar´as. Breakdown of diameter selectivity in a reductive hydrogenation reaction of single-walled carbon nanotubes. Chem.
Phys. Lett., 618:214, 2015.
Other publications:
1. G. Inzelt, Z. Pusk´as, K. N´emeth and I. Varga. Electrochemically induced trans-formation of ruthenium(III) trichloride microcrystals in salt solutions. J Solid State Electrochem., 9:823, 2005.
2. G. Inzelt, K. N´emeth and A. R´oka. Electrochemical quartz crystal microbalance study of redox transformations of TCNQ microcrystals in concentrated LiCl so-lutions. Electrochimica Acta, 52:4015, 2007.
3. H.-M. T´oh´ati, B. Botka, K. N´emeth, ´A. Pekker, R. Hackl and K. Kamar´as. In-frared and Raman investigation of carbon nanotube-polyallyamine hybrid sys-tems. Phys. Status Solidi B, 247:2884, 2010.
4. E. A. Francis, S. Scharinger, K. N´emeth, K. Kamar´as and C. A. Kuntscher. In-vestigation of the Jahn–Teller effect in the C−60 monoanion under high pressure.
Phys. Status Solidi B, 247:3047, 2010.
5. E. A. Francis, S. Scharinger, K. N´emeth, K. Kamar´as and C. A. Kuntscher.
Pressure-induced transition from the dynamic to static Jahn–Teller effect in (Ph4P)2IC60. Phys. Rev. B, 85:195428, 2012.
6. B. Botka, M. E. F¨ust¨os, H. M. T´oh´ati, K. N´emeth, G. Klupp, Z. Szekr´enyes, D. Kocsis, M. Utcz´as, E. Sz´ekely, T. V´aczi, G. Tarczay, R. Hackl, T. W. Cham-berlain, A. N. Khlobystov and K. Kamar´as. Interactions and chemical transfor-mations of coronene inside and outside carbon nanotubes. Small, 10:1369, 2014.
7. C. M¨uller, K. N´emeth, S. Vesztergom, T. Pajkossy and T. Jacob. The in-terface between HOPG and 1-butyl-3-methyl-imidazolium hexafluorophosphate.
Phys. Chem. Chem. Phys., submitted.
Posters:
1. K. N´emeth, F. Borondics, E. Jakab, ´A. Pekker, K. Kamar´as, S. Pekker:
Sidewall functionalization of HiPCo nanotubes in toluene IWEPNM, Kirchberg in Tirol, Austria (2008)
2. K. N´emeth, F. Borondics, E. Jakab, ´A. Pekker, K. Kamar´as, S. Pekker:
Reductive functionalization of HiPCo nanotubes SIWAN, Szeged, Hungary (2008)
3. K. N´emeth, ´A. Pekker, F. Borondics, K. Kamar´as, S. Pekker:
Infrared and Raman spectra of hydrogenated HiPCo nanotubes IWEPNM, Kirchberg in Tirol, Austria (2010)
4. K. N´emeth, ´A. Pekker, F. Borondics, K. Kamar´as, S. Pekker:
Sidewall functionalization of HiPCo single-walled carbon nanotubes FISS, Krutyn, Poland (2010)
5. K. N´emeth, ´A. Pekker, F. Borondics, K. Kamar´as, S. Pekker:
Investigation of diameter selectivity of reductive hydrogenation on single-walled carbon nanotubes
IWEPNM, Kirchberg in Tirol, Austria (2012)
6. H.-M. T´oh´ati, B. Botka, K. N´emeth, ´A. Pekker, K. Kamar´as:
Infrared and Raman investigation of carbon nanotube-based hybrid systems IWEPNM, Kirchberg in Tirol, Austria (2010)
7. E. A. Francis, S. Scharinger, K. N´emeth, K. Kamar´as, C. A. Kuntscher:
Investigation of the Jahn–Teller effect in C−60 monoanion under high pressure by infrared spectroscopy
IWEPNM, Kirchberg in Tirol, Austria (2010) 8. H.-M. T´oh´ati, K. N´emeth, ´A. Pekker, K. Kamar´as:
Infrared measurements on carbon nanotube-poly(allylamine hydrochloride) hy-brid systems
FISS, Krutyn, Poland (2010)
9. H.-M. T´oh´ati, K. N´emeth, K. Kamar´as, S. Ben-Valid, A. Zeng, L. Reiss, S.
Yitzchaik, M. Pietraszkiewicz, O. Pieraszkiewicz, L. Maggini, D. Bonifazi:
Infrared spectroscopic investigation on non-covalently functionalized single walled carbon nanotubes
ACN’2011, St. Petersburg, Russia (2011) 10. H.-M. T´oh´ati, K. N´emeth, K. Kamar´as:
Wide range optical study on double-walled carbon nanotubes prepared from sep-arated outer tubes
IWEPNM, Kirchberg in Tirol, Austria (2012)
Oral presentations:
1. K. N´emeth, A. Francis:
Synthesis of (Ph4P)2C60I
Mini-Workshop on ”Synthesis and spectroscopic characterization of carbon nanos-tructures”, Augsburg, Germany (2009)
2. K. N´emeth, A. Francis, M. Gy˝ori, P. Matus, K. Kamar´as:
Synthesis and infrared measurements of (Ph4P)2C60I and TDAE-C60
Mini-Workshop on ”Synthesis and spectroscopic characterization of carbon nanos-tructures”, Augsburg, Germany (2010)
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