TiO2-based materials are the most commonly used semiconductor
oxide photocatalysts due to their low environmental impact.
However, there are numerous obstacles impeding the maximization
of photocatalytic activity in these materials, including low
adsorption ability, detrimental recombination of charge carriers,
and light utilization [1,2]. In the past few decades, doping with
metal ions, coupling with a second semiconductor, and anchoring
TiO2 particles onto large-surface-area materials, such as mesoporous
materials, zeolites or carbon-based materials, have all been
elucidated as efficient techniques to improve the photodegradability
of semiconductor oxide photocatalysts [3–5]. Among them,
TiO2/carbon nanotube composites have been established as viable
potential photocatalysts for use in both water and air purifications
[6–8]. The synergetic effect of carbon nanotubes on photocatalyst
enhancement, in which carbon nanotubes act as the electron sink
for the hindrance of charge carrier recombination [6] or as the photosensitizer
to generate a greater density of electron/hole pairs [7],
has been previously demonstrated. Carbon nanotubes also behave
as impurities, resulting in the formation of Ti–O–C bonds and,
therefore, expanding the light absorption to longer wavelengths