A New Perspective in the Use of FeOx-TiO2 Photocatalytic Films: Indole Degradation in the Absence of Fe-Leaching

The study addresses the degradation of Indole under low intensity solar simulated light. The first evidence is presented for sputtered films degrading Indole at the solid-air interface. The co-sputtering of FeOx-TiO2 on polyethylene (PE) leads to an accelerated Indole degradation kinetics compared to TiO2-PE and FeOx-PE films. Indole degradation on TiO2-PE, FeOx-PE and polyethylene (PE) supported photocatalysts is shown to proceed without Fe- or Ti-release as detected by inductively coupled plasma mass spectrometry (ICP-MS). This opens a new perspective for the use of Fe-containing films in the degradation of pollutants. The mechanism of charge generation by TiO2-FeOx-PE film under light irradiation as a function of the applied light intensity provides insight and is discussed in relation to Indole degradation. The photo-generated charges in the film give rise to highly oxidative radicals which were unambiguously identified by appropriate scavenging experiments. The most oxidative species was O-singlet presenting an estimated lifetime of similar to 20 mu s and a mean-free path of similar to 140 nm. The probability of the Indole triplet deactivation was 0.01 and was much smaller compared to the probability of 0.99 for the Indole*-triplet reaction with O-2 dissolved in the aqueous solution. By attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), the systematic shift of v(s)(NH) and the v(s)(C=C) vibration rotational peaks were followed during Indole degradation presenting the evidence for the increase in the inter-bond distance and molecular fluidity. The increase in the film hydrophilicity during the irradiation was evaluated and seems to be necessary for the Indole degradation. An average size of similar to 16.7 nm of the TiO2-FeOx nanoparticles sputtered for 2 min on the PE was determined by atomic force microscopy (AFM) and remained invariable during the degradation of Indole. By Energy Dispersive Wavelength (EDW) a random distribution of FeOx and TiO2 in the FeOx-TiO2-PE films was seen. This study suggests a FeOx-TiO2 heterojunction inducing interfacial charge transfer (IFCT) from FeOx to the lower-lying TiO2 trapping states. (C) 2016 Elsevier Inc. All rights reserved.