Рік видавництва: 2019
Рік видавництва: 2019
Laser-induced crystallization of titanium dioxide nanotubular layers for photocatalytic applications
I. Mirza1, H. Sopha2, J.M. Macak2, A.V. Bulgakov1, N.M. Bulgakova1, O. Novak1, H. Turcicova1, A. Endo3, T. Mocek1
1HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech Republic
2Centre of Materials and Nanotechnologies, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic
3Faculty of Science and Engineering, Waseda University- Shinjuku-ku, Tokyo, Japan
During the last two decades, the photocatalytic application of titanium dioxide (TiO2 or titania) has received much attention for water purification and other environmental problem [1,2]. For such applications, the crystalline structure of material is a crucial parameter, since the amorphous phase may contains various kinds of defects in large quantity. These defects lead to recombination and trapping of photo-generated electron-hole pairs well before they can be involved in a chemical reaction . Titanium dioxide has three main crystalline phases, anatase, rutile and brookite . It has been shown that the anatase phase of nanocrystalline particles is much more functional in dye-sensitized solar cells . Among titania nanomaterials, nanotube layers are one of the most promising structures, which represent several mm long nanotube (NTs) arrays with large surface areas.
Highly ordered Titania NT layers can be grown in fluoride ion containing electrolytes and as-formed anodic nanotubes have an amorphous structure . Their dimensions (length and diameter) can be significantly be varied by adjusting the growth conditions. Thermal annealing is one of the most frequently used methods for crystallization of amorphous TiO2 nanomaterials. However, it is an energy-intensive method and needs several hours of treatment at a few hundred degrees Celsius. Under thermal annealing, amorphous titania transforms typically to a mixture of anatase and rutile. Increasing the annealing temperature leads to a higher rutile fraction in the mixed rutile-anatase phase [6,7]. Therefore, a fast energy-efficient method, which can crystallize NT layers into desired anatase phase in a non-destructive way, is highly beneficial in this field. In this work, we will present the results of laser-induced crystallization and photoelectrochemical properties of crystallized titania NT layers. For crystallization of NT samples, picosecond UV pulses with accumulative dose of few kJ cm-2 were applied. X-ray diffraction and Raman spectroscopy analysis of NT layers show the anatase phase with a negligible fraction of rutile under optimal irradiation conditions. Influence of laser processing parameters (laser fluence, accumulative energy dose, repetition rate) will be discussed.
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