CNT–TiO₂ core–shell structure: synthesis and photoelectrochemical characterization

Abstract

CNT–TiO2 core–shell nanostructured coatings were made using a hybrid CVD/ALD process. The evaluation of these films as photoanodes for the photoelectrochemical water splitting reaction reveals a clear benefit from the involvement of CNTs.

Supported nanostructured photocatalysts: the role of support-photocatalyst interactions

“…Furthermore, the formation of interfacial C-O-Ti bond can introduce energy levels in the bandgap of TiO 2 , which allow absorption of low-energy photons [96]. Furthermore, the formation of an interfacial C-O-Ti bond upon annealing of CNTs@TiO 2 material [97] could affect the interfacial charge transport and hence the photocatalytic and photoelectric properties of the composite material [98,99]. Likewise, visible light absorption has been reported for rGO-supported titania [100][101][102].…”

“…Furthermore, due to high electron mobility and small bandgap (0.5 eV, semiconducting) [94,95], CNTs act as sensitizers (participate in light absorption) and electron sinks for photogenerated electrons. Their high electron affinity (work function = 5.0-5.1 eV [181]), high electrons storage ability [177], and the availability of anti-bonding π* orbitals (highly conjugated system) make it possible for CNTs to trap the photoexcited electrons from the CB of MOs, thus reducing e − /h + recombination in the later and enhancing its photoactivity [48,98,176]. Furthermore, the additional formation of Ti-O-C/Ti-C defect states in TiO 2 -CNTs nanocomposites leads to absorption of visible light [182].…”

“…In general, two categories of CNTs/TiO 2 hetero-composites have been reported where the first one consists of intermixed CNTs and TiO 2 heterostructures [93,176], and the second one constitutes CNTs@TiO 2 core@shell materials where titania is coated or deposited on the surface of CNTs support [98,99]. Here our primary focus is on CNTs@ TiO 2 heterostructures, where the addition of the CNTs can enhance the photocatalytic response of TiO 2 in four possible ways.…”

“…Moreover, selective adsorption of specific adsorbates can be achieved through surface modification of the CNTs [48]. Secondly and most importantly, the enhancement in photoactivity of CNTs-TiO 2 arises from the ability of CNTs to act as conductive support or electron transport channel, withdrawing the photoexcited electrons from TiO 2 and thus retarding e − /h + recombination [98,176,183,184] (Fig. 11a).…”

“…11c) [96]. Furthermore, the formation of an interfacial C-O-Ti bond upon annealing has been observed in CNTs@TiO 2 material [99], which assists in interfacial charge transport, and this positively affects the photocatalytic and photoelectric properties of the CNTs@TiO 2 nanostructures [98,99]. Furthermore, this interfacial bonding alters the electronic structure at the interface, leading to a stronger bond between the TiO 2 and CNTs [99].…”