Single-wall carbon nanotubes (SWCNTs) have various remarkable properties, which make them a promising candidate for many applications. However, their inherent hydrophobicity have limited their commercial use in optical, biological, and electrical applications. Photo-initiated chemical vapor 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 SWCNT having surfaces properties ranging from superhydrophilic (CA<5°) to superhydrophobic (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).

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 photoactive 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, off-line GC-MS and on-line 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 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.

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