Hydrogen in Chemical Vapour Deposited Carbon Nanotubes: An Active Site for Functionalization

The presence of hydrogen in as-grown carbon nanotubes (CNTs) synthesized by microwave plasma (MP) chemical vapour deposition (CVD) technique is demonstrated. Our results showed that the MPCVD, as-grown CNTs were hydrogenated consisting of C—H bonds; whereas, the tubes synthesized by arc discharge consisted of non-hydrogenated multi-walled CNTs. Fourier transform infrared spectroscopy (FTIR) and micro-Raman spectroscopy techniques were used to detect C—H bonding in the as-grown CNTs. The effective functionalization of as-grown hydrogenated CNTs grown using a microwave CVD process is first time demonstrated by laser assisted CVD process. It was found that the laser-assisted CVD process resulted in the termination of hydrogen and the oxidation of as-grown CNT structure leading to the carboxylic group attachment. The FTIR results show the presence of —OH and C=O bonds in the functionalized samples. However, the non-hydrogenated CNTs could not be effectively functionalized by the same process, probably due to the fact that it did not contain active sites pre-requisite for functionalization, as did the CVD grown samples. The functionalization of CVD grown tubes is believed to take place at the 'active' hydrogen-terminated sites on the CNT surfaces.