Effect of doping and codoping with Mn and Fe on the photocatalytic performance of TiO2 thin films

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Copyright: Lin, Ming-Ze
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Abstract
TiO2 thin films with varying levels of Mn and Fe dopants (0.01 - 5.00 mol% metal basis for each) were deposited on soda-lime-silica glass substrates by spin coating, followed by annealing in air at 450°C for 2 h. Both single cation doping and codoping were carried out to investigate the effects of these additions on the photocatalytic performance of TiO2 thin films. The mineralogical, morphological, topographical, optical and photocatalytic properties were assessed for the films using glancing angle X-ray diffraction (GAXRD), field emission scanning electron microscopy (FESEM), atomic force microscopy, UV-VIS spectroscopy and methylene blue degradation tests. GAXRD analysis showed that anatase was the major phase in essentially all the films; no characteristic peaks representing any oxide of Mn or Fe were seen and this is attributed to either the incorporation of the dopants in the crystalline structure of titania or the low dopant concentrations being below the level of detection. A slight decrease in the degree of crystallinity with increasing Mn and Fe codopant concentrations, as shown in the GAXRD patterns, and a shift in the anatase peak locations in the laser Raman spectra suggested that solid solution formation occurred. All of the deposited films were of a consistent thickness of ~250 nm, as determined by transmission electron microscopy (TEM) imaging. FESEM and AFM analyses showed that the films were comprised of grains with sizes in the range of 20-30 nm. The doping appears to trigger agglomeration and coarse roughening of the films. UV-VIS spectrophotometry analysis revealed that all of the films were transparent (~80%) in the visible region and the optical indirect band gaps were ~3.4 eV. The photocatalytic performance as measured in terms of the degradation of methylene blue (MB) solution (≤24 h), showed that the extent photodegradation was generally degraded with increasing dopant concentrations. Only 0.01 mol% Fe-doped TiO2 film appeared to possess superior photoactivity than the undoped TiO2. This indicates that most samples probably were overdoped. Hence, improvement in the performance through band gap reduction through doping is likely to require low doping levels in order to minimise the number of electron/hole recombination centres and to minimise lattice distortion, both of which are deleterious to the performance.
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Author(s)
Lin, Ming-Ze
Supervisor(s)
Sorrell, Charles
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Publication Year
2014
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Thesis
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Masters Thesis
UNSW Faculty
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