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Hydrogenation, purification, and unzipping of carbon nanotubes by reaction with molecular hydrogen: road to graphane nanoribbons
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
NanoMaterials Group, Department of Applied Physics and Center for New Materials Aalto University, Aalto, Espoo, Finland.
NanoMaterials Group, Department of Applied Physics and Center for New Materials Aalto University, Aalto, Espoo, Finland.
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2011 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 5, no 6, 5132-5140 p.Article in journal (Refereed) Published
Abstract [en]

Reaction of single-walled carbon nanotubes (SWNTs) with hydrogen gas was studied in a temperature interval of 400-550 C and at hydrogen pressure of 50 bar. Hydrogenation of nanotubes was observed for samples treated at 400-450 C with about 1/3 of carbon atoms forming covalent C-H bonds, whereas hydrogen treatment at higher temperatures (550 C) occurs as an etching. Unzipping of some SWNTs into graphene nanoribbons is observed as a result of hydrogenation at 400-550 C. Annealing in hydrogen gas at elevated conditions for prolonged periods of time (72 h) is demonstrated to result also in nanotube opening, purification of nanotubes from amorphous carbon, and removal of carbon coatings from Fe catalyst particles, which allows their complete elimination by acid treatment.

Place, publisher, year, edition, pages
2011. Vol. 5, no 6, 5132-5140 p.
Keyword [en]
carbon nanotube, SWNT, hydrogen, graphene, graphane
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-46643DOI: 10.1021/nn201224kOAI: oai:DiVA.org:umu-46643DiVA: diva2:439676
Available from: 2011-09-08 Created: 2011-09-08 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Materials for Hydrogen storage and synthesis of new materials by hydrogenation
Open this publication in new window or tab >>Materials for Hydrogen storage and synthesis of new materials by hydrogenation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Material för vätelagring och syntes av nya material genom hydrering
Abstract [en]

The search for new materials for hydrogen storage is important for the development of future hydrogen energy applications. In this Thesis, it is shown that new materials with interesting properties can be synthesized by the reaction of hydrogen with various nanocarbon precursors. The thesis consists of two parts. The first part is devoted to studies of hydrogen storage in some metal-organic frameworks (MOFs) and nanostructured carbon materials, while the second part describes synthesis of new materials by the reaction of hydrogen gas with various carbon materials (i.e. fullerene C60, single-walled carbon nanotubes (SWCNTs), and fullerene C60 encapsulated inside SWCNTs (C60@SWCNTs)).

Hydrogen adsorption was measured for a set of Zn- and Co-based MOFs at near ambient temperatures. MOFs synthesized using different metal clusters and organic connecting ligands allowed to study effects of different surface area, pore volume, and pore shapes on hydrogen storage parameters. Hydrogen adsorption values in the studied MOFs correlated well with surface area and pore volume but did not exceed 0,75wt.%. Therefore, new methods to improve the hydrogen storage capacity in MOFs were investigated. The addition of metal catalysts was previously reported to improve significantly hydrogen storage in MOFs. In this thesis the effect of Pt catalyst addition on hydrogen adsorption in MOF-5 was not confirmed. Contrary to previous reports, hydrogen adsorption in MOF-5 mixed/modified with Pt catalysts had fast kinetics, correlated well with surface area, and was on the same level as for unmodified MOF-5. New nanostructured carbon materials were synthesized by the reaction between fullerene C60 and coronene/anthracene. Despite negligible surface area these materials adsorbed up to 0,45wt.% of hydrogen at ambient temperatures.

The reaction of fullerene C60 with hydrogen gas was studied at elevated temperatures and hydrogen pressures. In situ gravimetric monitoring of the reaction was performed in a broad temperature interval with/without addition of metal catalysts (i.e. Pt and Ni). The reaction resulted in synthesis of hydrogenated fullerenes C60Hx (with x≤56) followed by fullerene cage fragmentation and collapse upon prolonged duration of hydrogen treatment. Possible mechanisms of C60 hydrogenation and fragmentation were discussed. It is demonstrated that reaction of SWCNTs with hydrogen gas at elevated temperatures and hydrogen pressures can be used for nanotube opening, purification from amorphous carbon, side-wall hydrogenation, and partial unzipping of SWCNTs. Some graphene nanoribbons (GNRs) were synthesized as the result of SWCNTs unzipping. A surprising ability of hydrogen to penetrate inside SWNTs and to react with encapsulated fullerene C60 was demonstrated.

Abstract [sv]

Sökandet efter nya material för vätelagring är viktigt för utveckling av framtida väteenergitillämpningar. I denna avhandling visas att nya material med intressanta egenskaper kan syntetiseras genom reaktion av väte med olika nanokolprekursorer. Avhandlingen består av två delar. Den första delen ägnas åt studier av vätelagring i vissa metall-organiska fackverk (så kallade MOFs) och nanostrukturerade kolmaterial medan den andra delen beskriver syntes av nya material genom reaktion av vätgas med olika kolmaterial (dvs. fulleren C60, enkelväggiga kolnanorör (SWCNTs) och fulleren C60 kapslat i SWCNTs (C60 @ SWCNTs)).

Väteadsorptionen mättes för ett antal Zn- och Co-baserade MOFs vid rumstemperatur. MOFs syntetiserades med hjälp av olika metallkluster och organiska ligander för att studera effekterna av olika yta, porvolym och porformer på vätelagringsparametrarna. Väteadsorptionsvärden i de studerade MOFs korrelerade väl med yta och porvolym, men översteg inte 0,75wt.%. Därför undersöktes nya metoder för att förbättra kapaciteten för vätelagring i MOFs. Tillsättning av metallkatalysatorer har tidigare rapporterats avsevärt förbättra vätelagring i MOFs. I denna avhandling kunde effekten av en tillsats av Pt-katalysator på väteadsorption i MOF-5 inte bekräftas. I motsats till tidigare rapporter hade väteadsorption i MOF-5 blandad/modifierad med Pt-katalysatorer snabb kinetik och korrelerade väl med arean, men var på samma nivå som för omodifierad MOF-5. Nya nanostrukturerade kolmaterial syntetiserades genom reaktion mellan fulleren C60 och coronene/antracene. Trots försumbar yta adsorberade dessa material upp till 0,45wt.% väte vid rumstemperatur.

Reaktionen av fulleren C60 med vätgas studerades vid förhöjda temperaturer och vätetryck. In situ gravimetrisk övervakning av reaktionen utfördes i ett brett temperaturintervall med/utan tillsats av metallkatalysatorer (dvs. Pt och Ni). Reaktionen resulterade i syntes av hydrogenerade fullerener C60Hx (med x≤56) följt av fragmentering och kollaps av fullerenstrukturen vid förlängd varaktighet av vätebehandlingen. Möjliga mekanismer för hydrering och fragmentering av C60 diskuteras. Det har visats att reaktionen mellan SWCNTs och vätgas vid förhöjda temperaturer och vätetryck kan användas för öppning av nanorör, borttagning av amorft kol, funktionalisering av sidoväggar och partiell "blixtlåsöppning" av SWCNTs. Reaktionen kan också syntetisera grafen-nanoband (GNRs) som en följd av att SWCNTs öppnas på längden. En överraskande stor förmåga för väte att tränga in i SWNT och där reagera med inkapslade fullerenmolekyler C60 demonstrerades.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2012. 85 p.
Keyword
Fullerene C60, MOFs, CNTs, SWCNTs, PAHs, peapods, hydrogen, hydrogen storage, hydrogenation, adsorption, surface area, pore volume, spillover, nanoribbons, fragmentation
National Category
Physical Sciences
Research subject
Physical Chemistry; Physics
Identifiers
urn:nbn:se:umu:diva-58663 (URN)978-91-7459-463-8 (ISBN)
Public defence
2012-09-28, Naturvetarhuset, N300, Umeå Universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2012-09-07 Created: 2012-09-04 Last updated: 2012-09-05Bibliographically approved

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