Charge carrier dynamics and photocatalytic behavior of TiO sub(2) nanopowders submitted to hydrothermal or conventional heat treatment

• Published in: RSC advances Vol. 5; no. 86; pp. 70536 - 70545
• Main Authors: Patrocinio, AOT, Schneider, J, Franca, MD, Santos, L M, Caixeta, B P, Machado, AEH, Bahnemann, D W
• Format: Journal Article
• Language: English
• Published: 01.08.2015
• Subjects: Evolution; Heat treatment; Oxidation; Photocatalysis; Photocatalysts; Photonics; Surface area; Titanium dioxide
• ISSN: 2046-2069
• DOI: 10.1039/c5ra13291f

The sol-gel technique followed by conventional (TiO sub(2)-1) and hydrothermal (TiO sub(2)-2) thermal treatment was employed to prepare TiO sub(2)-based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO sub(2) surfaces and H sub(2) evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from transient absorption spectroscopy (TAS). TiO sub(2)-2 exhibits smaller particle size, poorer crystallinity, and higher surface area than TiO sub(2)-1. Moreover the hydrothermal treatment leads to formation of the metastable brookite phase, while TiO sub(2)-1 exhibits only the anatase phase. TAS measurements show that the electron/hole recombination of TiO sub(2)-2 is faster than that of the latter. Despite that, TiO sub(2)-2 exhibits higher photonic efficiencies for photocatalytic oxidation reactions, which is attributed to its larger surface area that compensates for the decrease of the surface charge carrier concentration. For H sub(2) evolution, it was found that the surface area has only a minor effect and the photocatalyst performance is controlled by the efficiency of the electron transfer to the platinum islands. This process is facilitated by the higher crystallinity of TiO sub(2)-1, which exhibits higher photonic efficiency for H sub(2) evolution than that observed for TiO sub(2)-2. The results found here provide new insights into the correlations between thermal treatment conditions and photocatalytic activity and will be useful for the design of high performance photocatalysts.