Enhanced photocatalytic properties of lanthanide-TiO2 nanotubes: An experimental and theoretical study

•During the electrochemical process, new Ho-f states below the CB of TiO2 is formed.•RE-TiO2 system leads to toluene degradation under LEDs λ = 465 nm irradiation.•Superoxide radicals are responsible for pollutant degradation over RE-NTs.

A series of Er-, Yb-, Ho-, Tb-, Gd-, Pr-TiO2 nanotubes (RE-NTs) was prepared via an electrochemical method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis absorption, scanning electron microscopy (SEM) and luminescent spectroscopy. The experiments demonstrated that toluene in the gas phase was successfully degraded under visible light (LEDs λmax = 465 nm) using RE-NTs. In the presence of the most active sample (Ho-NTs), the photodegradation of toluene reached 30% after 60 min of vis irradiation. To investigate the localization of RE in the TiO2 structure, computer simulations were performed using the plane-wave-based Vienna ab-initio simulation package (VASP) implementing spin-polarized density-functional theory (DFT) and the generalized gradient approximation (GGA). It is proposed that during the electrochemical process, TiO2 systems with new Ho-f states below the conduction band of TiO2 is formed. The photocatalytic activity under Vis irradiation is attributable not to OH but to other forms of reactive oxygen species (O2−, HO2, H2O2).

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