In this report we study the effect of annealing temperature on the structural stability, phase transformation and photo-electrochemical performance of TiO2 multi-leg nanotubes. Multi-leg nanotubes were synthesized using electrochemical anodization method, and as synthesized nanotubes were annealed in air at the temperatures ranging from 500 to 900 °C.We observed that multi-leg morphology is preserved upto 900 °C and a dominant rutile phase is observed at this temperature. X-ray diffraction and Raman spectra measurements were carried out to study the crystallite size, phase transformation and phonon confinement effects. The multi-leg nanotubes annealed at 900 °C shows enhanced photo-electrochemical performance; this is attributed to mixed phase, increase in crystallite size and decrease in defects. © 2016 Elsevier B.V.

Manu Jaiswal

Department Of Physics

Somnath Chanda Roy

Yalavarthi Rambabu

Annealing

Crystallite size

Oxide minerals

Phase Transitions

Photocurrents

stability

Titanium dioxide

X ray diffraction

Yarn

Effect of annealing

ELECTRO-CHEMICAL ANODIZATION

Electrochemical performance

PHONON CONFINEMENT EFFECT

PHOTOELECTROCHEMICALS

SPECTRA MEASUREMENTS

Structural stabilities

SYNTHESIZED NANOTUBES

Nanotubes

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Catalysis Today

Recombination of photo-generated charges is one of the most significant challenges in designing efficient photo-anode for photo electrochemical water oxidation. In the case of TiO2, mixed phase (anatase-rutile) junctions often shown to be more effective in suppressing electron-hole recombination compared to a single (anatase or rutile) phase. Here, we report the study of bulk and surface recombination process in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers, through an analysis of the photo-current and impedance characteristics. To quantify the charge transport/transfer process involved in these junctions, holes arriving at the interface of semiconductor/electrolyte were collected by adding H2O2 to the electrolyte. This enabled us to interpret the bulk and surface recombination process involved in anatase/rutile/rGO junctions for photo-electrochemical water oxidation. We correlated this quantification to the electrochemical impedance spectroscopy (EIS) measurements, and showed that in anatase/rutile junction the increase in PEC performance was due to suppression in electron-hole recombination rate at the surface states that effectively enhances the hole transfer rate to the electrolyte. On the other hand, in rGO wrapped A-R MLNTs junction it was due to both phenomenon i.e decrease in bulk recombination rate as well as increase in hole transfer rate to the electrolyte at the semiconductor/electrolyte interface. © 2016 Author(s).

Fulltext

AIP Advances

Probing the charge recombination in rGO decorated mixed phase (anatase-rutile) TiO2 multi-leg nanotubes

An annealing temperature-driven appearance of a sharp dual-band edge in the ultraviolet-visible absorption spectrum of electrochemically anodized TiO2 nanotubes (TNTs) and the corresponding impact on the photodegradation of organic dyes is reported based on the evolution of an anatase (A)/rutile (R) phase junction. Systematic X-ray diffraction followed by a micro-Raman analysis illustrates the impact of annealing between 500 and 900 °C in promoting the anatase-to-rutile phase transformation with a higher degree of crystallinity through an evolution of an intermediate mixed phase. X-ray photoelectron spectroscopy (XPS) further reveals a clear transition from the sub-stoichiometric to stoichiometric TNTs with increasing annealing temperature. Moreover, the valence band (VB) XPS along with the ultraviolet photoelectron spectroscopy (UPS) analysis suggests the possible band alignment at the A/R interface, whereas the X-ray absorption spectroscopy (XAS) at the Ti L- and O K-edges confirms a systematic change from an anatase to a rutile phase owing to the modification in local symmetry. To validate our experimental results, especially the formation of a dual-band edge at the A/R phase junction in TNTs, theoretical calculations using density functional theory (DFT) were also performed. Here, a one-to-one analysis of our theoretical and experimental results not only shows a good agreement to each other but also illustrates the microscopic origin behind the formation of a dual-band edge in mixed phase TNTs as well as the observed variation in Raman and XPS spectra with annealing temperature. Finally, an improved photocatalytic degradation of methylene blue aqueous solution is demonstrated in the presence of a mixed phase and explained in the framework of an efficient transfer of photogenerated electrons from the conduction band (CB) of R to the CB of A and holes from the VB of A to the VB of R across the phase junction in tube walls. © 2021 American Chemical Society.

Journal of Physical Chemistry C

Unveiling Temperature-Mediated Dual-Band Edge in TiO2Nanotubes with Enhanced Photocatalytic Effect

Multi-leg TiO2 nanotubes have been synthesised by electrochemical anodisation of Ti foils with suitable optimisation of the electrolyte (containing NH4F and HF) composition and concentration. As a result, multi-leg nanotube morphology shows a 4-fold enhancement in photocurrent density compared with that of compact tubes of comparable length under UV-VIS (320-500 nm) light illumination. We attribute this enhancement in photocurrent to efficient light scattering within the multi-leg morphology and the availability of a large contact area with the electrolyte compared to that of compact nanotubes. A model has been presented for light trapping and scattering ability on the basis of the graded refractive index behaviour associated with multi-leg nanotubes. Such graded refractive index behaviour is found to reduce specular reflectance, leading to a greater scattering of light into the nanotube structure. The diffused reflectance spectra confirm higher scattering in the multi-leg nanotube arrays, which indicates greater light harvesting by the multi-leg nanotube arrays. © 2015 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Enhanced photoelectrochemical performance of multi-leg TiO2 nanotubes through efficient light harvesting

The Journal of Physical Chemistry C

Heat Treatment Effect on Crystalline Structure and Photoelectrochemical Properties of Anodic TiO2 Nanotube Arrays Formed in Ethylene Glycol and Glycerol Based Electrolytes

Scientific Reports

Why is anatase a better photocatalyst than rutile? - Model studies on epitaxial TiO2 films

Journal of Applied Physics

Micro-Raman study on the softening and stiffening of phonons in rutile titanium dioxide film: Competing effects of structural defects, crystallite size, and lattice strain

Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting

Effect of annealing temperature on the phase transition, structural stability and photo-electrochemical performance of TiO2 multi-leg nanotubes

Journal	Data powered by TypesetCatalysis Today
Publisher	Data powered by TypesetElsevier B.V.
ISSN	09205861
Open Access	No