Functionalization of multiwalled carbon nanotubes by mild aqueous sonication

Sonication has been widely used in the dispersal of carbon nanotubes (CNTs) in various liquids as well as in their functionalization in aqueous acids. Here, for the first time, we study the sonication of multiwalled CNTs (MWCNTs) in deionized water. Our results indicate an improvement in the aqueous dispersal of MWCNTs as well as an increase in their adhesive interaction with Au substrates. Field emission scanning electron and high-resolution transmission electron microscopies as well as X-ray photoclectron, photoacoustic Fourier transform IR, and Raman spectroscopies have shown this to be due to the production of low concentrations of O-containing functionalizations (alcohol, carbonyl, acid, with the total O concentration being similar to 2%), without damaging the basic CNT structure; this production of functional groups is mirrored by the disappearance of -CHn groups existing on the pristine CNTs. These new functional groups are capable of hydrogen bonding, which plays an important role in their aqueous dispersal and enhanced substrate interactions.