Browsing by Subject "Dip coating"

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Open Access
An experimental and first-principles study of the effect of B / N doping in TiO2 thin films for visible light photo-catalysis
(Elsevier, 2013) Uddin, M. N.; Shibly, S. U. A.; Ovali, R.; Saiful, I.; Islam, M. S.; Uddin, M. J.; Gulseren, O.; Bengu, E.; Mazumder, M. M. R.
Thin films of TiO2 and boron-nitrogen (B/N) co-doped TiO 2 on glass substrates have been prepared by a simple sol-gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV-vis spectroscopy. The TiO 2 thin films with co-doping of different B/N atomic ratios (0.27-20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO 2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV-vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results. © 2013 Elsevier B.V.
Open Access
Synthesis of stable mesostructured coupled semiconductor thin films: meso-CdS-TiO2 and meso-CdSe-TiO2
(2010) Okur, H. İ.; Türker, Y.; Dag, Ö.
Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced self-assembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H20)4] (N03)2, HNO3, and Ti(OC4H 9)4 and then aging the samples under 50% humidity at 30 0C (denoted as meso-xCd(II)-y TiO2). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H 2S (or H2Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H2S (or H2Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H2S or H2Se gas). However, this problem can be overcome by further aging the samples at 130 °C for a few hours before H2S (or H2Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO2. However, the H2Se reaction, additionally, needs to be carried at lower H2Se pressures in an N2 atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-.yTiO2. Otherwise, an excessive number of Se8 particles form in the film samples.