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Iron doped titanate nanotubes for photocatalytic applications

Introduction Photocatalysis is one advanced oxidation technology with increasing potential for water and wastewater treatment. Among the many semiconductor photocatalysts, TiO2 has proven to be one of the best performance materials. Earlier studies of nanocrystalline TiO2 powders have shown that the introduction of metal ions: Fe, Cr, Co, Mo and V in the structure of TiO2 reduces the energy band- gap, and thereby increases the absorption in the visible region of the solar spectrum [1, 2]. In this work we prepared titanate nanotubes and doped them by iron with the aim to increase their photocatalytic activity and thus enable enhanced photocatalytic properties. Methods Titanatne nanotubes (TiNT - H) were synthesized by hydrothermal processing of anatase TiO2 and a concentrated NaOH solution. TiNT-H were further treated by a concentrated solution of Fe(OH)3, the treatment was repeated 1-3 times with the aim to incorporate different amounts of Fe ions in the structure of the prepared nanotubes (samples 1-3). In addition, sample 4 was prepared by Fe(OH)3 treatment of larger amount of TiNT. (HR)TEM techniques were used to determine the morphology and structure of the obtained Fe-TiNT and the amount of incorporated Fe ions. These results were compared with Raman spectroscopy and XRD observations. The heterogeneous photocatalytic degradation of diphenhydramine pharmaceutical, assisted in some cases with H2O2, was used as prove reaction. Results and discussion HRTEM measurements showed that in sample 1 there was only one mechanism of inbuilt of Fe. It seems that Fe ions were inbuilt in the nanotube structure between the titanate layers, so in this way the largest possible doping was 2%. In sample 2 the Fe ions were inbuilt in nanotubes, but also the small nanocristallites were attached at the surface of the nanotubes. In such regions about 6% of Fe was observed by EDXS measurement. In sample 3 the second mechanism of doping by nanoparticles formation at the surface of TiNT was dominated. Moreover, in some regions of sample 3 iron or iron hydroxide nanoparticles were observed as free standing. In sample 4 only TiNT with inbuilt Fe ions or nanoparticles attached at TiNT were observed. Raman spectra of samples 2, 3 and 4 showed only one band in addition to the bands of titanate nanoutubes, while there were no additional XRD lines observed. The best photocatalytic performances were observed for samples FeTiNT-1 and FeTiNT-4 as the most active materials and those that more efficiently use hydrogen peroxide. This observation can be explained by the decrease of the catalytic performance in the case of free standing iron based nanoparticles. Conclusion Two mechanisms of doping titanate nanotubes by iron were observed ; incorporation in the crystal lattice of TiNT probably between titanate layers, or formation of nanoparticles attached at the surface of the nanotubes. The photocatalytic properties of iron doped titanate nanotubes are related with the doping mechanism and with the presence of the free standing iron based nanoparticles in the sampe. References 1) J.C. Yu, J.G. Yu, W.K. Ho, Z.T. Jiang, L.Z. Zhang, Chem. Mater. 2002 ; 14, 3808. 2) W. Choi, A. Termin, M.R. Hoffmann, J. Phys. Chem. 1994 ; 98, 13669.

irone doped titanate nanotubes; photo catalysis; TEM

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