Abstract
Vertically oriented, self-organized TiO2–MnO2 nanotube arrays were successfully obtained by one-step anodic oxidation of Ti–Mn alloys in an ethylene glycol-based electrolyte. The as-prepared samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV-Vis absorption, photoluminescence spectroscopy, X-ray diffraction (XRD), and micro-Raman spectroscopy. The effect of the applied potential (30–50 V), manganese content in the alloy (5–15 wt. %) and water content in the electrolyte (2–10 vol. %) on the morphology and photocatalytic properties was investigated for the first time. The photoactivity was assessed in the toluene removal reaction under visible light, using low-powered LEDs as an irradiation source (λmax = 465 nm). Morphology analysis showed that samples consisted of auto-aligned nanotubes over the surface of the alloy, their dimensions were: diameter = 76–118 nm, length = 1.0–3.4 μm and wall thickness = 8–11 nm. It was found that the increase in the applied potential led to increase the dimensions while the increase in the content of manganese in the alloy brought to shorter nanotubes. Notably, all samples were photoactive under the influence of visible light and the highest degradation achieved after 60 min of irradiation was 43%. The excitation mechanism of TiO2–MnO2 NTs under visible light was presented, pointing out the importance of MnO2 species for the generation of e− and h+.
Highlights
TiO2 -based photocatalysis is an effective technique for pollutant removal from both gas and liquid phase [1,2,3,4,5,6,7]
The absorption band edge of pure TiO2 NTs at about 400 nm registered a red-shift at about 500 nm which is easier to appreciate in samples prepared from alloys with 15% of Mn
This was observed in the case of mesoporous structured MnO2 /TiO2 nanocomposites [39]. As it was stated by Ding, et al [59], TiO2 –MnO2 NTs could be used for solar-light driven photocatalysis owing to their absorption in the and 2017, visible region
Summary
TiO2 -based photocatalysis is an effective technique for pollutant removal from both gas and liquid phase [1,2,3,4,5,6,7]. Et al [45] synthesized ordered arrays of mixed oxide NTs by anodization of Ti/Mn alloys, under ultrasonication in the presence of a fluoride-containing ethylene glycol solution They pointed out that before calcination, the as-formed NTs showed a stoichiometry of (Ti,Mn)O2 , while annealing at 500 ◦ C resulted in formation of nanotubes composed of anatase and rutile phases of TiO2 and Mn2 O3. Wang, Yu, Li, and Zhao [32] electrochemically prepared mixed oxide NTs from Ti–Mn alloys which showed enhanced capacitive properties compared with those of pristine TiO2 NTs. this work aims to anodically grow TiO2 –MnO2 NTs in a fluoride-containing ethylene glycol-based electrolyte, and their application in the photodegradation of a model gaseous pollutant. Photodegradation tests in the gas phase were conducted with toluene as the model pollutant, and a possible mechanism of visible-light driven decomposition over the TiO2 –MnO2 NTs was proposed as well
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