log in log in register Register
English Français Deutsche Espaņol Italiano Korean

Project Abstract

Commercially available carbon nanotubes (CNTs) currently receive much attention from scientists in many disciplines, for very different applications. However, some of these suffer from the lack of reactivity of the CNTs. In order to overcome this issue, different methods to 'activate' or 'functionalize' their surface, such as conventional wet chemistry (use of acids) [Satishkumar, J. Phys. D: Appl. Phys. 29, 3173 (1996)], treatment in reactive gas atmosphere [An, Appl. Phys. Lett., 80, 4235 (2002)], electrochemistry [Wang, Chem. Phys. Lett., 407, 68 (2005)], etc. have been studied. Among the proposed methods for surface modification, the cold-low pressure RF plasma has been tested by the " Laboratoire Interdisciplinaire de Spectroscopie Electronique " of Namur University (LISE, FUNDP, BELGIUM), co-ordinator of this project, to successfully bind in a controlled way oxygen, amine and fluorine groups on the CNTs; theoretical modelling has already helped to understand the different reactivity of some chemical functions for CNTs with fixed curvature [Felten, J. Appl. Phys., 98, 074308 (2005)]. At the present time, very promising application of the plasma modified CNTs as gas sensors operating at room temperature have been also demonstrated [Bittencourt, Sensors & Actuators. B, 115:33 (2006); Ionescu, Sensors & Actuators. B, 113:36 (2006)].

The possibility to tune the plasma discharge operating parameters (gas composition, pressure, plasma power and duration...) combined with its diagnostic methods (Optical Emission Spectrometry, Mass spectrometry) allow us to fine tune and understand the physical properties of these treatments. As a result, a further experiment confirmed that it is possible to control the interfacial (structural and chemical) defects that control the deposition and growth of metal nanoclusters deposited on CNTs by using a plasma treatment. It is important to highlight that real control of the metal nanocluster growth on the carbon nanotubes appears possible, hence the acronym nano2hybrids.

In parallel to our experimental work, interaction of metal nanoclusters with CNTs has been modelled with different techniques, showing whether or not and in which conditions there are charge transfer and chemical bonds between the cluster and the CNT surface [Maiti, Chem. Phys. Lett., 395, 7 (2004)].

The cited proof of principle, combined with the knowledge that highly dispersed metal nanoparticles should bear a very high reactivity suggests that the association of these two nanotechnologies can be an important building block for new catalyst systems. The reactivity of metal particles can be controlled by modulating metal-support interaction and finite size (undercoordination) effects [Biener Surf. Sc., 590, L259 (2005)]. Bearing in mind that cold plasma treatment inducing structural and chemical defects, allows the control of the interfacial physico-chemistry, diffusion processes and stabilization of metal atoms/clusters (with metal atoms in different under-coordination), on the highly curved CNTs surfaces, it can be proposed that the use of plasma functionalization will permit to tailor important characteristics of the hybrid system aiming application in catalysis or/and in devices based on catalytic reactions such as chemical gas sensors. In fact, the cluster morphology is dictated by the relative interactions between the deposited atoms and the CNT surface; large binding energy between atoms and the CNT surface will lead to a higher nucleation density and a quasi continuous coverage or wetting of the CNTs; on the contrary, for a weaker interaction -or a larger metal to metal interaction- isolated metal nanoclusters will develop on the CNTs [Zhang, Chem. Phys. Lett. 331, 35 (2000)]. However, the interaction between clusters and CNT surface can change if defects are present. Thus, fine control of the local defects (type: structural or chemical; density) can be used to tune the interfacial properties of the metal clusters, that will determine their size and shape (which will dictate their electronic properties), diffusion (or not) avoiding aggregation, coalescence and complete wetting.

The underlying physics of the application of low temperature, low- vacuum and atmospheric- reactive pressure plasmas as a versatile nanofabrication tool [K. Ostrokov, Rev. Mod. Phys. 77, 489 (2005)] should be studied in more details, as it appears competitive compared to electrochemical deposition and to the other methods cited in [Guo, J. Coll. Interf. Sc. 286, 274 (2005)]. Plasma treatment doesn't use (large quantity of) polluting chemicals and is scalable to industrial production, especially within the atmospheric plasma design. Moreover, this treatment requires only few seconds or minutes to be efficient, compared to hours or days required by classical methods used to functionalize CNTs. It is important to mention that industrial production of nanotubes is now achieved (e.g. Nanocyl Co, http://www.nanocyl.com), with reasonable (reproducible) control of CNT characteristics. Moreover, large scale (industrial) applications are foreseeable in catalysis [Yin, J. of Catalysis, 224, 384 (2004)], fuel cells [Baughman, Science, 297, 787 (2002)], gas sensors [Zhao, Nanoletters 5, 847 (2005)], biomaterials [Meng, Nanomed.: Nanotech., Biol. & Med., 2, 136, 2005]...

By combining synthesis, characterization, theoretical modelling, practical testing and industrial applications with feedback to synthesis for optimization of the nano2hybrids materials - we will develop three different schemes, using plasma treatments at different (laboratory and industrial) scales, that will allow control of the chemistry, structure, diffusion and energetics at interfaces comprising metal nanoclusters and (modified) carbon nanotubes. We focus on the following scientific, technological, and societal objectives: