Ming Xia Xu

Preparation of TiO2 Thin Films Using Inorganic Peroxo Titanic Complex and Autoclaved Sols as Precursors

A new sol-gel method was introduced to prepare titanium oxides (TiO2) photocatalytic thin flms using peroxide (H2O2) and titanyl sulfate (TiOSO4) as raw materials. The TiOSO4 solution was recipitated by adding ammonia solution, then peptized with 30% H2O2 solution to get a yellow, table, neutral, and transparent liquid (peroxo titanic complex sol). When the peroxo titanic complex sol was autoclaved above 80°C for 2h, it changed to a stable, semitransparent sol containing eedle-like, ultra-fine anatase crystals less than 20nm in diameter. Titanium oxide (anatase) films sed for photocatalysis can be prepared on substrates by a dip-coating technique using peroxo titanic omplex and autoclaved sols.

Preparation and Properties of Titanium Oxide Photocatalyst with Visible Light Activity

TiO2 photocatalyst were obtained from the hydrolysis product of TiOSO4 with ammonia and the photocatalytic activities were investigated by the photocatalytic degradation of methyl orange aqueous solution under UV-light and visible-light. The results showed that the absorption intensity in visible-light was dependent on the concentration of the materials, pH value and heat-treatment temperature. The color of the TiO2 varied from yellowish to vivid yellow when the TiO2 was calcined at different temperatures from 300°C to 500°C for 1h. The photocatalytic activity of TiO2 under visible light was determined by the photo-absorption feature in visible light region, which was related to the heattreatment temperature. The TiO2 calcined at 400°C shows stronger photo-absorption in visible light region and exhibits higher visible-light activity than the TiO2 calcined at other temperature.

Preparation of a New Red Long Afterglow Phosphor Strontium Aluminate Composition

A new red afterglow phosphor Sr3Al2O6: Eu2+, Dy3+ was synthesized by solid-state reaction and sintered at 1150°C for 2h in reducing atmosphere. Red long lasting phosphorescence of the prepared materials is observed in the dark with naked eye after the removal of the excitation light. From the photoluminescence spectra, the broad emission band centered at 612 nm is confirmed. Excitation band chiefly lies in visible range and its maximum peak is at 473nm. Luminescence mechanism is studied.

Strength of Liquid-Phase-Sintering Cordierite Ceramics

The high dense pure cordierite ceramics and liquid-phase-sintering cordierite ceramics were prepared with the starting powder made by sol-gel progress. The porosities of them are less than 6.21%, and some can be up to 1.0% especially. The flexural strength of the sample can get to 167 MPa, which is greater than that of 103 MPa of pure cordierite ceramics. The composition, fracture behavior and microstructure of the liquid-phase-sintering cordierite ceramics are investigated. The result shows that the increased flexural strength is mainly attributed to the change in cell parameters of cordierite and the small grain size.

Synthesis and Characterization of Refluxed Sols and TiO2 Thin Films Using TiOSO4

Nano anatase TiO2 thin films on glass slide substrates were prepared via a dip-coating method using refluxed sols (RS) as precursors, then dried under infrared light and calcined at 500°C for 30min. The RS sols and TiO2 films were characterized by FT-IR, XRD, TEM, UV-Vis and SEM. The photocatalytic activities of the film samples were tested by the degradation of methyl orange solution with a concentration of 10mg/L under UV light irradiation. The results reveal that the RS sols are flavescent, alkalescent and contain needle-like anatase crystals. The TiO2 films are uniform, compact and transparent, their maximal light transmittance exceed 80% under visible light region. The degradation of methyl orange results illustrate that the RS-6 TiO2 thin films show the best photocatalytic activities, the decoloration rate of the methyl orange solution with RS-6 TiO2 thin films reachs 99% after irradiated 160min under UV light.

Microstructure Control and Phase Structure Study of Porous Alumina Membrane

A two-step anodization process was used to fabricate wide-range highly ordered porous anodic alumina membrane (PAA) in the electrolyte of oxalic acid through different anodic voltages. The effect of anodic voltage, pretreatments and pore-expanding time on the microstruture of PAA membrane was also studied in the process of two-step anodization. In a certain range, with the increase of anodic voltage, the pore diameter almost increases linearly while the pore density almost decreases linearly. The PAA template with anneal and electropolishing process has better regularity. In a certain time range, the pore diameter increases obviously with the pore-expanding time. It was demonstrated by XRD that the crystal constitution of the PAA without heat treatment was polycrystalline structure which contained Baehmite phase (Al2O3.H2O), Gibbsite phase (Al2O3.3H2O) and θ-Al2O3 phase. After heat treatment at 500°C for 0.5h, only the θ-Al2O3 phase was retained.

Study on Gas Sensing Properties of WO3 Thin Films

Tungsten oxide thin films were prepared by an inorganic-sol-gel dip-coating process, where the sol was obtained by adding citric acid, as chelating agent, to the ammonia solution of tungstic acid. The resultant thin films were a mixture of monoclinic and tetragonal phases of WO3 and, after being pretreated at 600°C and sintered at 650°C, the average grain size of the polycrystalline films was about 500 nm. The gas-sensing properties of WO3 thin films were tested at temperatures ranging from 500° to 600°C and in nitrogen gas containing 5vol% O2 or 5vol% H2. The WO3 sensors exhibited a good sensitivity and response speed at the temperature of 550°C.

Oxygen Sensitivity of SrFeO3-δ Thin Films Prepared by Sol-Gel Method

Sr(NO3)2, Fe(NO3)3 and citric acid (the mole ratio was 1:1:2) were mixed in water to form sol. Alumina substrate, which had been treated by ultrasonic cleaner, were dipped in the sol and pulled out, and the coating film was heated for 1h at 900oC. Through seventeen times treatment, SrFeO3-d thin film was coated on the alumina substrate. The remainder sol was dried and heated at 400oC, 800oC, 900oC for 2 h. The thin films and the powders were characterized by XRD. The morphologies of thin films were observed by SEM. The results showed that SrFeO3-δ was formed at 900oC on alumina substrate and the grain size was 100 ~ 200 nm. The oxygen sensitivity was measured in the temperature range of 377 ~ 577oC under different oxygen partial pressures. SrFeO3-δ thin film showed p-type conduction. The response time was less than 2 min when being exposed to a change from N2 to 0.466% O2 at 377oC.