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


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.



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Tobaldi, DM; Lajaunie, L; Rozman, N; Caetano, APF; Seabra, MP; Skapin, AS; Arenal, R; Labrincha, JA

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This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. David Maria Tobaldi is grateful to Portuguese national funds (OE), through FCT, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. We are obliged to Prof J Tedim and Prof LD Carlos (DEMaC/CICECO-Aveiro Institute of Materials and Physics Department and CICECO-Aveiro Institute of Materials, University of Aveiro, Portugal) for their constructive and fruitful discussions that improved the manuscript noticeably. The STEM and EELS measurements were performed in the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA) - Universidad de Zaragoza (Spain). R.A. gratefully acknowledges the support from the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P), from the Government of Aragon and the European Social Fund under the project Construyendo Europa desde Aragon 2014-2020 (grant number E/26). We also acknowledge financial support from the Slovenian Research Agency through the research programme No. P2-0273. Miss Dafne M Glaglanon is kindly acknowledged for proof-editing the English of the manuscript.

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