Papers by Keyword: Titania

Abstract: TiO₂ nanostructures with a pure anatase phase were successfully synthesized using hydrothermal treatment of P25-TiO₂ nanoparticles. These nanostructures were characterized using transmission electron microscopy (TEM) and x-ray powder diffraction measurements. The dependences of reaction temperature and calcination temperature on titanate-anatase phase transformation and the morphology of TiO₂ nanostructures were also discussed. The results demonstrated that phase composition and particle morphology can be controlled by both the reaction and calcination temperatures.

Abstract: A heterogeneous structured photo electrode using CDS -modified TiO₂ nanotube arrays (TNA) was fabricated. The CDS nano particles were precipitated by immersing TNA into NaS and Cd (ClO4)₂solution, where the number of immersion gave different amount of CDS precipitates. The effect of CDS on the performance of photochemical cell of TNA was evaluated. FESEM, EDS, XRD and UV-Visible were employed to characterize the structures and properties of CDS -modified TNA heterogeneous structure. The water splitting experiments were carried out using these CDS -modified TNA under standard AM 1.5 solar illumination (100mW/cm²>). An optimum hydrogen generation rate of 20.61μmole/cm²>)h (~0.50 ml/cm²>)h) was obtained. It was considered that the smaller band gap of CDS rendered the electrons a rapid transportation to the TiO₂nanotube arrays and the recombination of electron-hole was therefore effectively prevented. In summary, the CDS nano particles were effective in promoting the catalytic effect of TNA for hydrogen production.

Abstract: Titanium and its alloys find wide range of applications in aerospace, marine and automobile industries due to their excellent properties like high strength to weight ratio and good mechanical behaviour. Accordingly, the structural parts made of these alloys are being exposed to different corrosive environments. Therefore, the electrochemical stability of these structural parts needs to be significantly improved for their extended life time and effective functioning. The objective of the present work is to examine the effect of plasma electrolytic surface treatment in improving the corrosion resistance of Ti-6Al-4V in simulated acidic (0.5M H₂SO₄), marine (3.5% NaCl) and sulphur containing industrial (0.5M Na₂SO₄) environments. PEO is a relatively new technique for producing ceramic coatings on light metal alloys by employing higher voltage and current than anodizing. The Ti-6Al-4V was surface treated by plasma electrolytic oxidation (PEO) technique for 12 min under optimized conditions of electrical processing parameters and electrolyte chemistry. The logically selected electrolyte system consisting of 10 g of tri-sodium ortho phosphate (Na₃PO₄.12H₂O), 2 g of sodium meta silicate (Na₂SiO₃.9H₂O) and 2 g of potassium hydroxide (KOH) in 1 L of double distilled water was employed. The decisively optimized electrical parameters were fixed as 75% for the duty cycle, 1500 Hz for the pulse frequency and 0.1 A/cm² for the current density. The phase composition of the resulted coating was analyzed by the X-ray diffraction (XRD) technique. The coating thickness and the elemental composition of the coating were assessed using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). The corrosion characteristics were determined by potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) measurements. The XRD results demonstrated that the resulted coatings consisted of both anatase and rutile phases. The SEM results showed a coating thickness of about 15 µm and a canal like surface morphology with inter-connected open pores over the coating surface. The potentiodynamic polarization test results, in general, showed a minimum of about two orders of magnitude improvement in the corrosion resistance of the treated Ti-6Al-4V compared to that of the untreated in all the three corrosive environments. The EIS test results exhibit comparatively higher AC impedance and higher bode angle over the entire frequency range indicating an improved corrosion resistance of the surface treated Ti-6Al-4V. Thus the plasma electrolytic surface treatment with optimized process parameters, made the Ti-6Al-4V electrochemically stable by significantly improving its corrosion resistance in all the three environmental conditions.

Abstract: Uniform nanocrystalline pure anatase has been synthesized and characterized using tetrabutyl titanate aqueous solution as starting precursors by microwave hydrothermal method. The influences of synthesis conditions (reaction time and temperature) on the formation, crystal phase and crystallite size of TiO₂ has been investigated. A mixture solution of tetrabutyl titanate and normal butyl alcohol in 1:4 molar ratio is processed in a microwave hydrothermal autoclave at low temperature 120°C for different durations, at 200°C for 20 min to precipitate titania powders, respectively. It was revealed that uniformly dispersed and granulous single phase anatase prepared at 120°C for 180 min with the average particle size of 10 nm was formed by means of XRD and TEM.

Abstract: This work highlights the fabrication of multiwalled carbon nanotube (MWCNT)-TiO₂ nanocomposite for use in dye-sensitized solar cells (DSSCs) to improve the photovoltaic conversion efficiency. Morphology of the MWCNT-TiO₂ film was investigated by field emission scanning electron microscopy (FESEM). FESEM images demonstrated that MWCNTs were dispersed homogeneously in TiO₂ matrix. MWCNT acted as an efficient conduit for electron transfer that can enhance the photovoltaic conversion efficiency of the DSSC. The proposed MWCNT-TiO₂ nanocomposite photoelectrode might be beneficial to develop high photovoltaic conversion efficiency of DSSCs.

Abstract: In this paper, Cu-Ce/TiO₂ nano-particles, whose molar ratio account for 2%,2.5%,3%,3.5% and 4% respectively, were synthesized by sol-gel method, using Ti(C₄H₉O)₄ as the raw material, And the photocatalytic activities of the prepared samples were investigated by degrading formaldehyde gas under pure visible light through simulating indoor environment in the environmental test chamber. Moreover, X-Ray Powder Diffraction (XRD) and Ultraviolet-visible spectrophotometer were applied to analyze the crystallite size and optical properties of the samples. It is indicated that the sample of 2.5% performs best in the test. Besides, photocatalytic mechanism of co-doping of Cu-Ce was discussed.

Abstract: N-doped titania was synthesized by a one step hydrothermal method, which is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The samples prepared by hydrothermal method demonstrate higher photocatalytic activity toward the degradation of methylene blue under xenon lamp which has similar spectra to solar light, and also is much superior to that of the commercial P25. In addition, the samples prepared by hydrothermal treatment could severely influence the crystal lattice structure. Morever, N-doped titania can further enhacnce the photocatalytic activity effectively, and hydrothermal treatment is a very suitable method for the synthesis of N-doped titania. This excellent performance could endow the as-prepared P-doped titania potential in purifying wastewater.

Abstract: TiO₂/Fe₂O₃ nanocomposite was fabricated by a hydrolysis-precipitation approach, with TiCl₄ as precursor and Fe₂O₃ as support. The crystal phase, diameter and morphology of the sample particle were characterized by X-ray diffraction, transmission electron microscope. The results show that the samples are composed of haematite and rutile. The morphology and diameter of rutile particle, coating effect and weight percentages of haematite and rutile are related to the preparing temperature and molar ratio of Fe/Ti. The photocatalytic activity of the prepared photocatalyst was estimated in an aqueous solution at ambient temperature of 303K. The results imply that the photocatalytic activity of the sample is higher than that of phase pure rutile, related to Fe/Ti molar ratio and its preparing temperature. These results can be attribute to the microsturcture of the sample. A synergistic effect exists between titania and haematite in the nanocomposite.

Abstract: TiO₂/CNTs nanocomposites with different Ti/C molar ratios were prepared by a sol-hydrolysis method at 368 K, using titanium tetrachloride as a precursor and nitrified carbon nanotubes as a support. The crystal phase, morphology and microstructure of the sample were characterized by X-ray Diffraction (XRD) and High-Resolution Transmission Electron Microscope (HRTEM). The photocatalytic activity of the samples was performed by methyl orange in aqueous solutions under UV light.The supernatant liquid of methyl orange during degradation was determined by using an UV-vis spectrophotometer (UV-vis). XRD results show that the crystal phases of the sample are composed of carbon nanotubes, anatase and rutile. HRTEM results show that the average diameter of oval titania is about 4.2 nm, and it decorates on the surface of carbon nanotubes uniformly. UV-vis results show that the photocatalytic activity of the TiO₂/CNTs nanocomposite with the optimum Ti/C molar ratio is much higher than that of P25. These results indicate that a synergistic effect exists between titania and carbon nanotubes in the nanocomposite.

Abstract: The present work is aimed at the optimisation of an electrolyte system for the development of an oxide layer on Ti-6Al-4V implant material by plasma electrolytic oxidation (PEO) process, to improve its corrosion resistance under 4.5 pH osteoclast bioresorption and 7.4 pH simulated body fluid physiological conditions. All the PEO experiments were conducted for 12 min in constant current mode by a DC power supply unit with 7 different electrolyte systems consisting of methodically varied concentrations of tri-sodium ortho phosphate (Na₃PO₄.12H₂O), sodium meta silicate (Na₂SiO₃.9H₂O) and potassium hydroxide (KOH). The phase composition of the fabricated oxide coatings was analyzed by X-ray diffraction (XRD) technique. The morphology and thickness of the coatings were determined by scanning electron microscopy (SEM) and the corrosion characteristics were assessed by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. The XRD results demonstrated that the oxide coatings mainly consisted of anatase and rutile phases with different proportions. While the average surface pore size was in the range of 3 to 6 µm, the thickness of the coating varied from 5 to 20 µm. A significant improvement in the corrosion resistance and an added capacitive nature was observed for the PEO treated Ti-6Al-4V implant material compared to that of the untreated. The variation in the proportions of anatase and rutile phases, the surface pore size distribution, the thickness of the coating and the corrosion characteristics of the developed coatings were correlated with the composition and concentration of the electrolyte system. Of the seven different electrolyte systems employed in the present study, the one consisting of 10 g Na₃PO₄.12H₂O, 2 g Na₂SiO₃.9H₂O and 2 g of KOH was established to be an optimized electrolyte system for developing oxide coatings on Ti-6Al-4V to minimise corrosion and thereby reduce the metal ion release under physiological conditions.