Surface studies of hydroxylated multi-wall carbon nanotubes

Robert H. Bradley, Kelby Cassidy, Rodney Andrews, Mark Meier, Susan Osbeck, Aurik Andreu, Colin Johnston, Alison Crossley

Research output: Contribution to journalArticle

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Abstract

CVD grown MWCNTs, of typical diameter 5 to 50 nm and with approximately 15–20 concentric graphene layers in the multi-walls, have been surface functionalised using the Fenton hydroxylation reaction. HRTEM reveals little physical difference between the treated and untreated materials; images from both exhibit similar multi-wall structure and contain evidence for some low-level disruption of the very outermost layers. Raman spectra from the two types of nanotubes are almost identical displaying the disorder (D) peaks at approximately 1350 cm−1 and graphite (G) peaks at approximately 1580 cm−1, characteristic of graphene-based carbon materials, in approximately equal intensity ratios. Equilibrium adsorption data for nitrogen at 77 K leads to BET surface areas of 60.4 m2 g−1 for the untreated and 71.8 m2 g−1 for the hydroxylated samples; the increase in area being due to separation of the tube-bundles during functionalization. This is accompanied by a decrease in measured porosity, mostly at high relative pressures of nitrogen, i.e. where larger (meso 2–5 nm and macro >5 nm) pores are being filled, which is consistent with an attendant loss of inter-tube capillarity. X-ray photoelectron spectroscopy (XPS) shows that hydroxylation increases the nanotube surface oxygen level from 4.3 at.% to 22.3 at.%; chemical shift data indicate that approximately 75% of that oxygen is present as hydroxyl (–OH) groups. Water vapour adsorption by the hydroxylated surfaces leads to Type II isotherms which are characteristic of relatively high numbers of hydrogen bonding interactions compared to the untreated materials which exhibit Type III curves. This difference in polar surface energy is confirmed by calorimetric enthalpies of immersion in water which are −54 mJ m−2 for the untreated and −192 mJm−2 for the hydroxylated materials. The treated materials therefore have significantly increased water wettability/dispersivity and a greater potential for cross-linking with matrix compounds. The mechanism by which hydroxylation occurs i.e. free radical (OHradical dot) attack and subsequent electrophilic addition at Cdouble bond; length as m-dashC bonds in the graphene basal planes, is discussed.
LanguageEnglish
Pages4835-4843
Number of pages9
JournalApplied Surface Science
Volume258
Issue number11
DOIs
Publication statusPublished - 15 Mar 2012

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Carbon Nanotubes
Graphite
Carbon nanotubes
Hydroxylation
Graphene
Nanotubes
Nitrogen
Oxygen
Adsorption
Water
Capillarity
Steam
Chemical shift
Free radicals
Interfacial energy
Hydroxyl Radical
Water vapor
Free Radicals
Isotherms
Macros

Keywords

  • multi-wall carbon nanotubes
  • functionalization
  • XPS
  • raman
  • HRTEM
  • adsorption
  • surface energy

Cite this

Bradley, R. H., Cassidy, K., Andrews, R., Meier, M., Osbeck, S., Andreu, A., ... Crossley, A. (2012). Surface studies of hydroxylated multi-wall carbon nanotubes. Applied Surface Science, 258(11), 4835-4843. https://doi.org/10.1016/j.apsusc.2012.01.008
Bradley, Robert H. ; Cassidy, Kelby ; Andrews, Rodney ; Meier, Mark ; Osbeck, Susan ; Andreu, Aurik ; Johnston, Colin ; Crossley, Alison. / Surface studies of hydroxylated multi-wall carbon nanotubes. In: Applied Surface Science. 2012 ; Vol. 258, No. 11. pp. 4835-4843.
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Bradley, RH, Cassidy, K, Andrews, R, Meier, M, Osbeck, S, Andreu, A, Johnston, C & Crossley, A 2012, 'Surface studies of hydroxylated multi-wall carbon nanotubes' Applied Surface Science, vol. 258, no. 11, pp. 4835-4843. https://doi.org/10.1016/j.apsusc.2012.01.008

Surface studies of hydroxylated multi-wall carbon nanotubes. / Bradley, Robert H.; Cassidy, Kelby; Andrews, Rodney; Meier, Mark; Osbeck, Susan; Andreu, Aurik; Johnston, Colin; Crossley, Alison.

In: Applied Surface Science, Vol. 258, No. 11, 15.03.2012, p. 4835-4843.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Surface studies of hydroxylated multi-wall carbon nanotubes

AU - Bradley, Robert H.

AU - Cassidy, Kelby

AU - Andrews, Rodney

AU - Meier, Mark

AU - Osbeck, Susan

AU - Andreu, Aurik

AU - Johnston, Colin

AU - Crossley, Alison

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N2 - CVD grown MWCNTs, of typical diameter 5 to 50 nm and with approximately 15–20 concentric graphene layers in the multi-walls, have been surface functionalised using the Fenton hydroxylation reaction. HRTEM reveals little physical difference between the treated and untreated materials; images from both exhibit similar multi-wall structure and contain evidence for some low-level disruption of the very outermost layers. Raman spectra from the two types of nanotubes are almost identical displaying the disorder (D) peaks at approximately 1350 cm−1 and graphite (G) peaks at approximately 1580 cm−1, characteristic of graphene-based carbon materials, in approximately equal intensity ratios. Equilibrium adsorption data for nitrogen at 77 K leads to BET surface areas of 60.4 m2 g−1 for the untreated and 71.8 m2 g−1 for the hydroxylated samples; the increase in area being due to separation of the tube-bundles during functionalization. This is accompanied by a decrease in measured porosity, mostly at high relative pressures of nitrogen, i.e. where larger (meso 2–5 nm and macro >5 nm) pores are being filled, which is consistent with an attendant loss of inter-tube capillarity. X-ray photoelectron spectroscopy (XPS) shows that hydroxylation increases the nanotube surface oxygen level from 4.3 at.% to 22.3 at.%; chemical shift data indicate that approximately 75% of that oxygen is present as hydroxyl (–OH) groups. Water vapour adsorption by the hydroxylated surfaces leads to Type II isotherms which are characteristic of relatively high numbers of hydrogen bonding interactions compared to the untreated materials which exhibit Type III curves. This difference in polar surface energy is confirmed by calorimetric enthalpies of immersion in water which are −54 mJ m−2 for the untreated and −192 mJm−2 for the hydroxylated materials. The treated materials therefore have significantly increased water wettability/dispersivity and a greater potential for cross-linking with matrix compounds. The mechanism by which hydroxylation occurs i.e. free radical (OHradical dot) attack and subsequent electrophilic addition at Cdouble bond; length as m-dashC bonds in the graphene basal planes, is discussed.

AB - CVD grown MWCNTs, of typical diameter 5 to 50 nm and with approximately 15–20 concentric graphene layers in the multi-walls, have been surface functionalised using the Fenton hydroxylation reaction. HRTEM reveals little physical difference between the treated and untreated materials; images from both exhibit similar multi-wall structure and contain evidence for some low-level disruption of the very outermost layers. Raman spectra from the two types of nanotubes are almost identical displaying the disorder (D) peaks at approximately 1350 cm−1 and graphite (G) peaks at approximately 1580 cm−1, characteristic of graphene-based carbon materials, in approximately equal intensity ratios. Equilibrium adsorption data for nitrogen at 77 K leads to BET surface areas of 60.4 m2 g−1 for the untreated and 71.8 m2 g−1 for the hydroxylated samples; the increase in area being due to separation of the tube-bundles during functionalization. This is accompanied by a decrease in measured porosity, mostly at high relative pressures of nitrogen, i.e. where larger (meso 2–5 nm and macro >5 nm) pores are being filled, which is consistent with an attendant loss of inter-tube capillarity. X-ray photoelectron spectroscopy (XPS) shows that hydroxylation increases the nanotube surface oxygen level from 4.3 at.% to 22.3 at.%; chemical shift data indicate that approximately 75% of that oxygen is present as hydroxyl (–OH) groups. Water vapour adsorption by the hydroxylated surfaces leads to Type II isotherms which are characteristic of relatively high numbers of hydrogen bonding interactions compared to the untreated materials which exhibit Type III curves. This difference in polar surface energy is confirmed by calorimetric enthalpies of immersion in water which are −54 mJ m−2 for the untreated and −192 mJm−2 for the hydroxylated materials. The treated materials therefore have significantly increased water wettability/dispersivity and a greater potential for cross-linking with matrix compounds. The mechanism by which hydroxylation occurs i.e. free radical (OHradical dot) attack and subsequent electrophilic addition at Cdouble bond; length as m-dashC bonds in the graphene basal planes, is discussed.

KW - multi-wall carbon nanotubes

KW - functionalization

KW - XPS

KW - raman

KW - HRTEM

KW - adsorption

KW - surface energy

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DO - 10.1016/j.apsusc.2012.01.008

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SP - 4835

EP - 4843

JO - Applied Surface Science

T2 - Applied Surface Science

JF - Applied Surface Science

SN - 0169-4332

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Bradley RH, Cassidy K, Andrews R, Meier M, Osbeck S, Andreu A et al. Surface studies of hydroxylated multi-wall carbon nanotubes. Applied Surface Science. 2012 Mar 15;258(11):4835-4843. https://doi.org/10.1016/j.apsusc.2012.01.008