X-Ray Photoelectron Spectroscopy of Anatase-TiO2 Coated Carbon Nanotubes

Abstract

A high efficiency nanocomposite photocatalyst is reported. Multiwall carbon nanotubes (MWNTs) were coated with titania. Two distinct types of nanocomposites were synthesized with variation in the synthetic procedure. One of the nanocomposites is based on a core of arc-discharge synthesized multiwall carbon nanotubes; whereas the other is based on a core of chemical vapor deposition (CVD) grown MWNTs. The nanocomposites have a similar appearance in transmission electron microscopy pictures in that they have a core of MWNTs that are chemically bonded to a few nanometer thick layer of pure anatase phase of titania. Yet they show a dramatically different photocatalytic behavior when they are compared on the basis of rates of photocatalytic decomposition of an organic dye in aqueous media following the Langmuir-Hinshelwood mechanism. This article focuses on the analysis of the differences in the nanocomposites using X-Ray Photoelectron Spectroscopy (XPS). XPS spectra of these materials indicate that there are distinct differences. However, they also show that both share C-O-Ti bonds that transform the carbon in the carbon nanotubes into a dopant for the anatase titania. This doping seems to be essential for long wavelength, i.e. visible light induced photocatalysis.