Modulation of the Work Function of TiO₂ Nanotubes by Nitrogen Doping: Implications for the Photocatalytic Degradation of Dyes

Abstract

The work function engineering in metal-oxide nanostructures by judicious doping of impurities is not straightforward as it introduces multiple defects in the system. In this regard, understanding the nitrogen (N) doping-induced modulation of Fermi levels in TiO2 nanotubes (TNTs) is challenging for visible-range photocatalytic applications. Here, 50 keV N ions are implanted in TNTs with a fluence range of 1014–1016 ions/cm2. X-ray diffraction and micro-Raman analyses demonstrate the formation of anatase-TiO2 in pristine TNTs, while the crystalline quality is significantly affected by increasing ion fluence. The evolution of Ti3+ is also established by X-ray photoelectron spectroscopy, whereas ultraviolet photoelectron spectroscopy reveals the reduction in work function due to the formation of oxygen vacancies, in good agreement with X-ray absorption spectroscopy and photoluminescence results. The electron paramagnetic resonance study further identifies the evolution of Ti3+/N-substitutional defect centers. Finally, an enhancement in visible-light-assisted methylene blue and Rhodamine B dye degradation is recorded up to a fluence of 1 × 1015 ions/cm2, and it is correlated with the N-ion implantation-induced formation of electrochemically active states near the conduction band minimum and the valence band maximum. The decrease in degradation efficiency beyond a critical fluence of 1015 ions/cm2 is discussed on the ground of ion-beam-mediated amorphization and the subsequent increase in electron–hole recombination in the defect states.

Hierarchical UiO-66(−NH2)/CuInS2 S-Scheme Photocatalyst with Controlled Topology for Enhanced Photocatalytic N2 Fixation and H2O2 Production

“…The UPS spectral analysis is performed using He I ( h ν = 21.22 eV) as the excitation energy. The work function of the pristine materials is calculated by subtracting the secondary electron cutoff energy from the He I energy. , The secondary cut off energy ( E cutoff ) for the bare UN66 and CIS is measured to be 16.15 and 16.78 eV, while the corresponding work function values (Φ) are calculated to be 5.07 and 4.44 eV, respectively (Figure S18). The CIS material has a lower work function as compared to the UN66 material.…”

A Review on Oxygen-deficient Titanium Oxide for Photocatalytic Hydrogen Production

“…Thus, introducing oxygen defects during the ion-doping process usually occurs unconsciously and controlling the density of oxygen defects is a great challenge. However, scientists can combine the advantages of ion doping and oxygen defects to improve the photocatalytic performance of TiO 2 [100,101].…”

Thermal Modulation in Nanostructured Materials for Advanced Applications

“…A material's capacity to conduct heat is indicated by its thermal conductivity (k). It measures how quickly heat moves through a substance when there is a temperature gradient [20]. Low thermal conductivity denotes ineffective heat transport, while high thermal conductivity denotes effective heat transfer.…”