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Impact of Rutile Fraction on TiO2 Visible-Light Absorption and Visible-Light-Induced Photocatalytic Activity

preprint
submitted on 13.12.2018 and posted on 14.12.2018 by David Maria Tobaldi, Luc Lajaunie, ana caetano, nejc rozman, Maria Paula Seabra, andrijana sever skapin, Raul Arenal, Joao Antonio Labrincha
Titanium dioxide is by far the most utilised semiconductor material for photocatalytic applications. Still, it is transparent to visible-light. Recently, it has been proved that a type-II band alignment for the rutile−anatase mixture would improve its visible-light absorption.
In this research paper we thoroughly characterised the real crystalline and amorphous phases of synthesised titanias – thermally treated at different temperatures to get distinct ratios of anatase-rutile-amorphous fraction – as well as that of three commercially available photocatalytic nano-TiO2.
The structural characterisation was done via advanced X-ray diffraction method, namely the Rietveld-RIR method, to attain a full quantitative phase analysis of the specimens. The microstructure was also investigated via an advanced X-ray method, the whole powder pattern modelling. These methods were validated combining advanced aberration-corrected scanning transmission microscopy and high-resolution electron energy-loss spectroscopy. The photocatalytic activity was assessed in the liquid- and gas-solid phase (employing rhodamine B and 4-chlorophenol, and isopropanol, respectively, as the organic substances to degrade) using a light source irradiating exclusively in the visible-range.
Optical spectroscopy showed that even a small fraction of rutile (2 wt%) is able to shift to lower energies the apparent optical band gap of an anatase-rutile mixed phase. But is this enough to attain a real photocatalytic activity promoted by merely visible-light?
We tried to give a reply to that question.
Photocatalytic activity results in the liquid-solid phase showed that a high surface hydroxylation led to specimen with superior visible light-induced catalytic activity (i.e. dye and ligand-to-metal charge transfer complexes sensitisation effects). That is: not photocatalysis sensu-strictu.
On the other hand, the gas-solid phase results showed that a higher amount of the rutile fraction (around 10 wt%), together with less recombination of the charge carriers, were more effective for an actual photocatalytic oxidation of isopropanol.

Funding

CICECO-Aveiro Institute of Materials

Fundação para a Ciência e Tecnologia

Find out more...

POCI-01-0145-FEDER-007679

MAT2016-79776-P

Slovenian Research Agency P2-0273

History

Email Address of Submitting Author

david.tobaldi@ua.pt

Institution

University of Aveiro

Country

Portugal

ORCID For Submitting Author

0000-0002-0112-8570

Declaration of Conflict of Interest

no conflict of interest

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