Beyond charge separation: The effect of coupling between titanium dioxide and CNTs on the adsorption and photocatalytic reduction of Cr(VI)

• Strongly-coupled composite particles made of TiO2 and CNTs were prepared.
• The particles were used to study photocatalytic reduction of Cr(VI).
• The functionalization of the CNTs affected the photocatalytic reduction rate.
• In the absence of sacrificial agents the CNTs serve as dual oxidation and reduction sites.
• Under these conditions easy transport of both carriers to the CNTs enhances reduction rate.

Composite particles comprised of titanium dioxide strongly coupled to various types of carbon nanotubes (CNTs) were prepared by low temperature hydrothermal synthesis.A significant enhancing effect on the photocatalytic reduction rate of Cr(VI) was observed, as a consequence of Cr(VI) adsorption on the CNTs. This rate-enhancing effect was shown to depend on the type of the CNTs and on their functionalization.While evidence for the presence of a synergistic effect is well documented, the comparison between the effects of the various types of CNTs enables to present a new phenomenon., connected to the fact that for this specific model system both reduction and oxidation occur mainly on the CNTs. Here, the extent by which the reduction rate will be enhanced depends not only upon the tendency of the CNTs to adsorb the Cr(VI), but also on the ability of the system to shuttle both holes and electrons to the CNTs, namely whether the CNTs are metallic or not.

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