Impact of the absolute rutile fraction on TiO2 visible-light absorption and visible-light-promoted photocatalytic activity

authors	Tobaldi, DM; Lajaunie, L; Rozman, N; Caetano, APF; Seabra, MP; Skapin, AS; Arenal, R; Labrincha, JA
nationality	International
journal	JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY
author keywords	Advanced X-ray methods; High-resolution electron energy-loss spectroscopy; Anatase-rutile mixture; Apparent optical band gap; Visible-light
keywords	QUANTITATIVE PHASE-ANALYSIS; AMORPHOUS CONTENT; BAND ALIGNMENT; ANATASE; TITANIA; OXIDATION; BROOKITE; NANOPARTICLES; DEGRADATION; PHOTODEGRADATION
abstract	Titanium dioxide is by far the most used 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 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. 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 an answer to that question. 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. Photocatalytic activity results in the liquid-solid phase showed that a high surface hydroxylation led to specimen with superior visible light-promoted catalytic activity - i.e. dye and ligand-to-metal charge transfer complexes sensitisation effects, not photocatalysis sensu-strictu. On the other hand, the gas-solid phase results showed that a higher amount of the absolute rutile fraction (around 10 wt%), together with less recombination of the charge carriers, were more effective for both visible-light absorption and a real visible-light promoted photocatalytic oxidation of isopropanol.
publisher	ELSEVIER SCIENCE SA
issn	1010-6030
year published	2019
volume	382
digital object identifier (doi)	10.1016/j.jphotochem.2019.111940
web of science category	Chemistry, Physical
subject category	Chemistry
unique article identifier	WOS:000481566700040