Functionalization of multi-walled carbon nanotubes using water-assisted chemical vapor deposition

A simple and novel method, water-assisted chemical vapor deposition (CVD) was developed to functionalize multi-walled carbon nanotubes (MWCNTs) during the synthesis process. The functionalized MWCNTs were characterized using Raman spectroscopy, XPS, TGA, NH3-TPD, SEM and HR-TEM. It was found that new defects are introduced and the amount of acidic groups is increased on the MWCNT surface during the water-assisted CVD process. The amount of C–OH and C–O group on the MWCNT surface is found to be increased from 21.1% to 42% with water vapor assistance. Density functional theory (DFT) was employed to study the chemical behavior of water vapor molecule on the catalyst particle surface of Ni(1 1 1) cluster. Based on the experimental and DFT simulation results, a mechanism for functionalization of MWCNTs by water-assisted CVD is proposed.

Graphical abstractWater is adsorbed and activated on Ni surface, then dissociated into OH and O species, followed by part of OH and O species desorbed from the surface. Finally, the desorbed OH and O species oxidize the unsaturated carbon atoms of carbon nanotubes, form defects and oxygen-containing groups.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► MWCNTs were functionalized by water-assisted CVD method. ► Defects and weak-medium acidic sites were created on the MWCNT sidewalls. ► Oxygen-containing groups in functionalized MWCNT were increased from 21.1% to 42%. ► A mechanism for the influence of water vapor on MWCNTs was proposed.