Syngas/Photo-Initiated Chemical Vapor Deposition to Modify Single-Walled Carbon Nanotubes

RÉSUMÉ: Dans la présente étude, nous détaillons le développement d'une méthode performante pour la fonctionnalisation de nanotubes de carbone mono-paroi (SWCNTs) à l'aide de dépôt chimique en phase vapeur photo-initié (PICVD) à base de syngaz (CO+H2) qui se montre efficace pourl'introduction d'une grande variété de groupes fonctionnels en surface. Les résultats mettent en évidence qu'en modifiant les paramètres expérimentaux de pression, de ratio molaire H2/CO, de temps de traitement et de la position du substrat dans le réacteur, la mouillabilité du matériaux peut être finement ajustée en passant d'hydrodophile à super-hydrophobe (que ce soit par modification de la densité des groupes fonctionnels ou encore par modification directe de la topologie de surface). De plus, une étude cinétique du procédé mis en oeuvre a été effectuée en phase gazeuse et en surface afin de comprendre l'effet et le comportement du traitement des SWCNTs, incluant le rôle de la température. Il a été déterminé que le pentacarbonyle de fer (l'impurité la plus abondante dans les cylindres de monoxyde de carbone) joue un rôle crucial dans le procédé puisqu'il est consommé à plus de 94% durant le traitement, contre 0% du CO et du H2 injectés dans le réacteur. Le bilan de matière du syngas/PICVD a été calculé en se basant sur la caractérisation de la phase gazeuse et de la surface des SWCNT. La composition chimique du matériel déposé a été identifiée comme étant du C38H5O43Fe14, avec une principale présence de groupes carboxyliques, hydroxyles, de Fe(CO)n et de Fe(OH)n. Sur la base des analyses et du bilan de masse ontenus, nous suggérons deux mécanismes distincts pour la chimie se déroulant en phase gazeuse (incluant 12 réactions) et en phase de surface (incluant 30 réactions)----------ABSTRACT: In the present study, a promising method has been developed to functionalize single-wall carbon nanotubes (SWCNTs) using photo-initiated chemical vapor deposition (PICVD) with syngas (CO+H2) and then applying it to form a full range of functional groups on the surface of the SWCNTs. It was observed that by changing the operating conditions, including pressure, the molar ratio of H2/CO, treatment time, and the position of the substrate inside the reactor, a wide range of wettability (caused either by functionality density or physical roughness of the coating)ranging from super-hydrophilic to super-hydrophobic can be obtained. A kinetic study of the syngas/PICVD process was then performed in both the gas and surface phases to understand the syngas/PICVD behavior in the treatment of SWCNTs. The influence of temperature on this process was also determined to gain more insight about the syngas/PICVD behavior on SWCNT treatment. We found that iron pentacarbonyl, the most common impurity in the carbon monoxide cylinder, played a very important role in this process considering that 94% is consumed during treatment, while at the same time carbon monoxide and hydrogen fed to the reactor was not consumed. The mass balance of syngas/PICVD was calculated based on the gas phase characterizations and surface phase analyses of SWCNTs. The chemical structure of the deposited coating was identified as C38H5O43Fe14 in the majority with mainly carboxylic, hydroxyl, Fe(CO)n, and Fe(OH)n chemical moieties. Based on the analyses and the obtained mass balance, two mechanisms were suggested for the gas phase (including 12 reactions) and surface phase (including 30 reactions) reactions, separately

Full range of wettability through surface modification of single-wall carbon nanotubes by photo-initiated chemical vapour deposition

Single-wall carbon nanotubes (SWCNTs) have various remarkable properties, which make them a promising candidate for many applications. However, their inherent hydrophobicity has limited their commercial use in optical, biological, and electrical applications. Photo-initiated chemical vapour deposition (PICVD) using syngas is proposed as a novel, affordable, and versatile method to tailor SWCNT wettability through the addition of oxygen-containing functional groups. Following PICVD surface treatment, X-ray photoelectron spectroscopy, water contact angle measurements (CA), thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy confirm controlled oxygenation of the SWCNT surface. Indeed, this novel approach allows to reproducibly make SWCNTs having surfaces properties ranging from superhydrophilic (CA 150°), including any intermediate values, by simply varying operational parameters such as molar ratio of the syngas precursor, photo-polymerization time and reactor pressure (about normal conditions)

Reaction kinetics and temperature effects in syngas photo-initiated chemical vapor deposition on single-walled carbon nanotubes

Photo-initiated chemical vapor deposition (PICVD) is a solvent-free process that can be used to produce thin films on a variety of substrates, with applications in fields ranging from biomedicine to optics and microelectronics. This study presents a kinetic analysis for this process using syngas (CO + H2) as a precursor for the surface treatment of single-walled carbon nanotubes (SWCNT) with average dimensions of 1.5 × 100 nm (diameter × length), and addresses the role of iron pentacarbonyl (Fe(CO)5), a photo-active contaminant found in CO. This work builds upon previously developed reaction schemes for PICVD, based mainly on surface characterizations, by coupling these analyses with gas-phase monitoring. This allows us to propose two separate reaction schemes for the gas and surface phase reactions and consider temperature effects. Online FTIR, offline GC-MS, and online GC characterized the gas phase, while for surface characterizations, XPS and TGA were used. Characterizations showed that a coating with a general formula of CnO3nFen was deposited, corresponding to 0.29 ± 0.04 mg carbon and 0.49 ± 0.03 mg iron on the SWCNT substrate over the course of treatment. The Fe(CO)5 was identified as the key reactant in syngas/PICVD reactions and was nearly completely consumed (94%). Mass balances derived from the gas phase characterization showed that Fe(CO)5 inputted to the plug flow reactor could potentially contribute all the amount of 0.49 ± 0.03 mg of Fe and 0.29 ± 0.04 mg of C to the coating on the SWCNT, indicating that syngas/PICVD can be optimized in the future to decrease gas throughput. Temperature did not show a significant effect in the case of PICVD. However, in the absence of ultraviolet light, its role becomes determinant, with rising temperatures causing more Fe deposition