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Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France. SRSMC, UMR CNRS-Université de Lorraine, Faculté des Sciences et Technologies, Vandoeuvre-lès-Nancy, France.
LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
LCPME, UMR CNRS-Université de Lorraine, Villers-lès-Nancy, France.
IJL, UMR CNRS-Université de Lorraine, Nancy Cedex, France.
Visa övriga samt affilieringar
2018 (Engelska)Ingår i: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 9, s. 2750-2762Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

Ort, förlag, år, upplaga, sidor
Beilstein-Institut , 2018. Vol. 9, s. 2750-2762
Nyckelord [en]
biosensing, carbon nanotubes, covalent functionalization, electrocatalysis, ferrocene
Nationell ämneskategori
Annan fysik
Forskningsämne
Experimentell fysik; Tillämpad fysik
Identifikatorer
URN: urn:nbn:se:ltu:diva-71587DOI: 10.3762/bjnano.9.257ISI: 000448782500001PubMedID: 30416926Scopus ID: 2-s2.0-85056284634OAI: oai:DiVA.org:ltu-71587DiVA, id: diva2:1263365
Anmärkning

Validerad;2018;Nivå 2;2018-11-15 (johcin)

Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-04-11Bibliografiskt granskad
Ingår i avhandling
1. Covalent functionalization of carbon nanomaterials for bioelectrochemical applications
Öppna denna publikation i ny flik eller fönster >>Covalent functionalization of carbon nanomaterials for bioelectrochemical applications
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Kovalent funktionalisering av kolnanomaterial för bioelektrokemiska tillämpningar
Abstract [en]

Carbon nanotubes (CTNs) are renowned for their exceptional electronic and mechanical properties. Their structure can be considered as rolling up a graphene sheet along a specific crystallographic direction, leading to a 1D confinement of the electronic wavefunction of the delocalized electrons along the perimeter of the cylindrical structure thus obtained. This confinement produces the existence of defined spikes of high intensity in the electronic density of states, called van Hove singularities. These singularities are primordial to understand both the optical and electronic properties of CNTs through electronphonon coupling processes. If the electronic density of states (DoS) is non zero at the Fermi level the nanotube is metallic, otherwise the nanotube is semiconducting. The synthesis of CNTs always produces a mixture of both metallic and semiconducting nanotubes, and this material can be useful to be incorporated at the surface of electrodes for electrochemical devices. The high specific surface area, the high mechanical and thermal stability of CNTs and the low percolation threshold for electron transport in a mat of CNTs render them very attractive for such kind of applications. There is yet a drawback of using raw CNTs: they are not compatible with solvents and modification of their surfaces by chemistry is required to make good suspensions for easy deposition at the electrode surface and to introduce specific functional groups for promoting electron transfer, called electron shuttles.

The final aim of this thesis is therefore the covalent functionalization of CNTs by electron shuttles and their incorporation at the surface of glassy carbon electrodes for electrochemical devices application. A strategy of chemical grafting in three steps has been chosen: i) a controlled oxidation step in acidic media assisted by microwave irradiation in order to keep the structural integrity of CNTs, so as to save their useful electronic properties; ii) a chloration step to produce acid chloride groups and iii) reaction of these groups with electron shuttles modified by specific linkers. The study was first conducted on very clean HiPCO single-walled CNTs (SWCNTs). This enabled to avoid any disturbing effects of carbonaceous impurities or residual catalytic particles, since their possible effects are extremely controversial in the literature. Once validated, this approach was then conducted with cheaper material including few-walls carbon nanotubes (FWCNTs). The use of FWCNTs compared to SWCNTs was not only beneficial for the production of costeffective electrochemical devices but also for a better durability ofthe final device, the inner nanotubes being not functionalized.

The challenge was to obtain a functionalization process with enough grafted electron shuttles to obtain a good electrocatalytic activity but maintaining CNTs integrity. The first step is predominant to reach this goal, and requires a very accurate understanding of the nature and the number of defects created in the CNTs structure versus the physico-chemical conditions used. The introduction of defects in the crystallographic structure of CNTs has strong consequences both for the electronic DoS and for the phononic properties of the material. Spectroscopic methods are essential in probing these consequences. UV-visible-near IR absorption spectroscopy is the method of choice to directly probe the existence of van Hove singularities and the oscillator strength associated with the authorized electronic transitions between theses ingularities. Covalent grafting of chemical groups at the surface of CNTs changes both the energy and the intensity of these transitions. However, this spectroscopic method requires solubilizing CNTs in non-absorbing solvents using adequate surfactants. Interactions between surfactant molecules and CNT sidewalls may also alter the position and intensity of electronic transitions between van Hove singularities unrelated to the chemical groups covalently grafted.

Raman spectroscopy of CNTs involves the electronphonon coupling processes through the resonant electronic enhancement of Raman modes. Double resonance processes are also observed in Raman spectrum of CNTs, for instance with the D-band mode that is actually related to the existence of defects in the graphene structure of CNTs. Therefore, Raman spectroscopy is a widespread analytical method to characterize the structural defects created by covalent functionalization processes. Indeed, the intensity ratio of the D and G bands in the Raman spectrum is correlated to the number of defects. However, CNTs are used as bundles when chemical functionalization is performed, which produces a heterogeneous distribution of chemical species grafted on CNTs. Therefore, we have developed a new protocol to obtain statistically significant data for most of the samples made in this thesis. Nevertheless, this statistical approach is still limited for samples slightly functionalized, whence the idea to use spectroscopic ellipsometry as an alternative method to characterize these samples.

More specifically, ellipsometric data were collected from UV to the IR part of the electromagnetic spectrum for CNTs functionalized in different conditions. The complex dielectric function was retrieved from the experimental data. A Drude model was used to model the infrared part of the data for raw and acid oxidized CNTs. The optical conductivity of the samples was obtained. These results, combined with other information collected using a set of complementary analytical techniques (Raman scattering, UV-visible-NIR absorption, X-ray photoelectron spectroscopy, thermogravimetric analysis coupled to mass spectrometry, transmission electron microscopy and rare gas volumetric adsorption), show that the microwave-assisted oxidation process actually consists in removing amorphous carbon deposits away from the surface of CNTs and transforming the already existing defects in the CNT structure to oxygen-containing groups such as carboxylic acids.

Rare gas volumetric adsorption was also used to compare the distribution of chemical groups at the surface of CNT bundles when two different acids are used (HNO3 and H2SO4). The chloration step was also studied by these methods, as well as the final grafting of electron shuttles. Finally, these functionalized CNTs were deposited at the surface of glassy carbon electrodes and used as electron mediators for diaphorase-catalysed oxidation of nicotinamide adenine dinucleotide (NADH). This was a good example of mediated electron transfer for development of electrochemical devices based on NADH recycling and it validated the good electrocatalytic properties of functionalized CNTs for making electrochemical sensors and actuators, opening new perspectives with potential market applications.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2019
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Annan fysik
Forskningsämne
Experimentell fysik
Identifikatorer
urn:nbn:se:ltu:diva-73331 (URN)978-91-7790-342-0 (ISBN)978-91-7790-343-7 (ISBN)
Disputation
E231, Luleå (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-03-27 Skapad: 2019-03-27 Senast uppdaterad: 2019-04-30Bibliografiskt granskad

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