Papers by Author: Xi Xin Wang

Abstract: CaWO₄ films were prepared in saturated Ca(OH)₂ solution through constant-voltage anodization method. Influences of reaction time, voltage and temperature on the morphology, crystal structure and photoluminescence properties were studied through scanning electron microscopy (SEM), X-ray diffractometer (XRD) and photoluminescence measurements (PL). Results show that the as-prepared CaWO₄ film is of tetragonal phase, the reaction conditions affect the morphology, grain size and photoluminescence properties greatly. The CaWO₄ film anodized at 20V, 45°C for 40 min is flat, uniform and dense with stronger photoluminescence intensity. The formation process of CaWO₄ films has also been discussed.

Abstract: Iron titanium oxides with different Ti:Fe ratios (molar ratio: 3:1, 2:1, 1:1, 1:2, 1:3) have been prepared by chemical coprecipitation process. The structures and properties of the samples have been characterized by X-ray diffraction, vibrating sample magnetometer and UV-vis spectrophotometer. Results show that the samples annealed at 460 °C have poor crystallinity. At 550 °C, the crystallinity of all the samples increased strikingly. The iron titanium oxides contained anatase TiO₂, rutile TiO₂, α-Fe₂O₃ and/or Fe₂TiO₅. Ti:Fe ratios have a great influence on the detailed phase compositions of each sample. The iron titanium oxides exhibited paramagnetism and the intensity of magnetization increased with the increasing content of Fe. Band gap energies of the oxides changed slightly with increasing content of Fe with an average value of 2.0 eV, obviously lower than that of TiO₂ .

Abstract: In this work, highly-ordered TiO₂ nanotube arrays were prepared by constant-voltage anodization, followed by electrodeposition of Ag to obtain Ag-loaded TiO₂ (Ag-TiO₂) nanotube arrays via alternating current (AC) process. The results of SEM and XRD show that the morphology and crystal structure of Ag-TiO₂ layer depend greatly on the electrodeposition parameters. Ag-TiO₂ nanotube arrays prepared in 2.5 mmol/L AgNO₃ solution by electrodeposition with applied voltage of 12 V for 1 minute performed the best photoelectrochemical current response and photocatalystic activity. The photocurrent density of Ag-TiO₂ is 43.32 μA/cm² under sunlight irradiation (70 mW/cm²), which is 4.2 times as that of unloaded TiO₂ nanotube arrays. Methyl orange (MO) degradation rate with the Ag-TiO₂ nanotube arrays achieves 52.13% after 90 min sunlight irradiation which is obvious higher than that of TiO₂ nanotube arrays. The mechanism of enhancing photoelectrochemical activity of decorating titania with Ag has also been discussed in the view of energy band theory.

Abstract: Titania nanotube arrays were synthesized via anodic oxidization of titanium foil in dimethyl sulfoxide (DMSO) solution containing 2 wt% HF and 3 wt% H2O at 40 V. The microstructure of the arrays was characterized with scanning electron microscopy (SEM). The results show that morphology of titania nanotube arrays is evidently influenced by the anodization time, and with the extension of oxidation time, the better morphology could be obtained. The possible formation mechanism of titania nanotube arrays has been discussed.

Abstract: BaTiO3 films with a thickness up to 3 μm were fabricated under the hydrothermal conditions. It was found that the crystallinity of BaTiO3 increases with the concentration of Ba(OH)2 solutions. Along with the increasing of time, the crystallinity of BaTiO3 increases, reaches the maximum value and then decreases. The measured values of remanent polarization (Pr) and coercive field (Ec) are 1.74μC/cm2 and 24KV/cm. The leakage of the films at 1V is 10-7A/cm2. The dielectric constant and loss tangent of hydrothermal derived BaTiO3 film at a frequency of 1 KHz were 600 and 0.2, respectively.

Abstract: Dispersing barium titanate (BT) in aqueous media has received special attention due to economic and environmental considerations. A new kind of dispersant named poly (acrylic acid-co-itaconic acid) has been synthesized in our study. By adjusting reactant ratio and reactant condition poly (acrylic acid-co-itaconic acid) with different average molecular (2000~10000) and different content of itaconic acid (10% ~ 30%) have been obtained. Dispersing effects of poly (acrylic acid-co-itaconic acid) have been studied through zeta potential, sediment experiments, rheological behavior. It can be concluded from our study poly (acrylic acid-co-itaconic acid) containing 20% itaconic acid with Mw between 3000 and 5000 show the best dispersing effect.