A Study on Doped Heterojunctions in TiO2 Nanotubes: An Efficient Photocatalyst for Solar Water Splitting

Abstract

The two important factors that affect sunlight assisted water splitting ability of TiO2 are its charge recombination and large band gap. We report the first demonstration of nitrogen doped triphase (anatase-rutile-brookite) TiO2 nanotubes as sun light active photocatalyst for water splitting with high quantum efficiency. Nitrogen doped triphase TiO2 nanotubes, corresponding to different nitrogen concentrations, are synthesized electrochemically. Increase in nitrogen concentration in triphase TiO2 nanotubes is found to induce brookite to anatase phase transformation. The variation in density of intra-band states (Ti3+ and N 2p states) with increase in nitrogen doping are found to be critical in tuning the photocatalytic activity of TiO2 nanotubes. The presence of bulk heterojunctions in single nanotube of different nitrogen doped TiO2 samples is confirmed from HRTEM analysis. The most active nitrogen doped triphase TiO2 nanotubes are found to be 12 times efficient compared to pristine triphase TiO2, for solar hydrogen generation. The band alignment and charge transfer pathways in nitrogen doped TiO2 with triphase heterojunctions are delineated. Bulk heterojunctions among the three phases present in the nanotubes with intra-band defect states is shown to enhance the photocatalytic activity tremendously. Our study also confirms the theory that three phase system is efficient in photocatalysis compared to two phase system.

N-Doped TiO2 Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma

“…On the basis of the existing literature, the shift effect is indicative of lattice disorder defects. It can be caused by oxygen vacancies, 29,30 the electronic interaction between titania and nitrogen doping, 27,31 or the change in particle size. 32,33 SEM is also employed to characterize the microstructure of the films and to provide more evidence about the shift in Raman spectra.…”

Titania nanotubes prepared by rapid breakdown anodization for photocatalytic decolorization of organic dyes under UV and natural solar light

“…The proposed formulas are shown in Eq. 1a – c below [ 16 , 35 , 36 ]. where W A , W B , and W R represent the weight fractions of anatase, brookite, and rutile.…”

Recent advances in the use of TiO2 nanotube powder in biological, environmental, and energy applications

“…92 Moreover, band gap engineering via doping, decoration and/or alloying with different elements (metals or non-metals) was reported to extend its light harvesting into the visible region of the solar spectrum. 93,94 David et al 95 reported the impact of loading TNTs, fabricated via rapid breakdown anodization, with Pt, Pd and Ni nanoparticles on the efficiency of hydrogen generation via solar water splitting. The as-prepared TNTs were annealed at 450 C for 3 h then sensitized with the metal nanoparticles through the chemical reduction approach using NaBH 4 .…”

“…This journal is © The Royal Society of Chemistry 2019 Nanoscale Adv., 2019, 1, 2801-2816 | 2807 Creative Commons Attribution 3.0 Unported Licence.from brookite to anatase. The photocatalytic measurements revealed that doping TiO 2 with a nitrogen concentration of 0.29 atomic percentage exhibited the best photocatalytic performance in hydrogen production (30.2 mmol g À1 ) via solar water splitting 94. …”