Effects of welding current on properties of A-TIG welded AZ31 magnesium alloy joints with TiO_2 coating

The effects of welding current on the macro-morphology, microstructure and mechanical properties of tungsten inert gas(TIG) welded AZ31 magnesium alloy joints with TiO2 coating were investigated. The results showed that the increase of welding current led to the increase in the depth/width ratio and deteriorated the surface appearance of the welded seams with TiO2 coating. The grain size of α-Mg and the amount of granular β-Mg17Al12 particles in the welded seams also increased. The welded joints with TiO2 coating exhibited a deeper weld penetration and larger grain size compared with the welded joint without TiO2 coating. When the welding current was less than 130 A, the ultimate tensile strength of the welded joints with TiO2 coating increased with the increase in welding current and then decreased when the welding current was greater than 130 A. The average microhardness of the heat-affected zone and fusion zone decreased gradually with the increase of welding current.

Morphology Control of Anatase TiO2 by Surfactant-assisted Hydrothermal Method

By hydrolysing titanium isopropoxide in a long hydrocarbon chain surfactant-containing solution, TiO2 fine particles with a diversity of well-defined morphologies was synthesized in this study by a hydrothermal route. The structural change during the formation process was monitored by scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. TiO2 with various morphologies such as particle, sheet, rod, tube and flower-like shape was obtained by carefully controlling the preparation conditions. The experimental results show that the pH value is crucial for shape control of the produced TiO2 because it can change the charge state of the surfactant in the solution and the adsorption potential of the surfactant on the TiO2 surface. The shape evolvement of anatase TiO2 was elucidated by quenching the reaction at different stage and the formation mechanism of different shaped TiO2 was suggested.

Photocatalytic Activity of N-doped TiO2 Photocatalysts Prepared from the Molecular Precursor （NH4）2TiO（C2O4）2

We developed a novel approach for the preparation of N-doped TiO2 photocatalysts by calcining ammonium titanium oxalate at different temperatures. The structures of N-TiO2 were characterized by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, diffuse reflectance UV-Vis spectroscopy, and scanning electron microscope. The N-doped TiO2 photocatalysts calcined below 700 ℃ are the pure anatase phase but that calcined at 700 ℃ is a mixture of anatase and rutile phases. The doped N locates at the interstitial site of TiO2 which leads to the narrowing of bad gap of pure anatase N-TiO2. Among all photocatalysts, N-TiO2 photocatalysts calcined at 600 and 400 ℃ exhibit the best performance in the photodegradation of methyl orange under the UV light and all-wavelength light illuminations, respectively; however, because of the perfect crystallinity and the existence of anatase-rutile phase junctions, N-TiO2 photocatalyst calcined at 700 ℃ exhibits the highest specific photodegradation rate, i.e., the highest quantum yield, under both the UV light and all-wavelength light illuminations.

Synthesis of TiO2 supported on activated carbon by MOCVD： operation parameters study

A novel metallo-organic chemical vapor deposition (MOCVD) technique has been applied to the preparation of the photocatalytic titanium dioxide supported on activated carbon. The effects of various condition parameters such as carrier gas flow rate, source temperature and deposition temperature on the deposition rate were investigated. The maximum deposition rate of 8.2 mg/(g.h) was obtained under conditions of carrier gas flow rate of 400 ml/min, source temperature of 423 K and deposition temperature of 913 K. The deposition rate followed Arrhenius behavior at temperature of 753 K to 913 K, corresponding to activation energy Ea of 51.09 kJ/mol. TiO2 existed only in anatase phase when the deposition temperature was 773 K to 973 K. With increase of deposition temperature from 1073 K to 1273 K, the rutile content sharply increased from 7% to 70%. It was found that a deposition temperature of 773 K and a higher source temperature of 448 K resulted in finely dispersed TiO2 particles, which were mainly in the range of 10-20 nm.

Meaningful comparison of photocatalytic properties of {001} and {101} faceted anatase TiO2 nanocrystals

The facet-dependent photocatalytic performance of TiO_2 nanocrystals has been extensively investigated due to their promising applications in renewable energy and environmental fields. However, the intrinsic distinction in the photocatalytic oxidation activities between the {001}and {101} facets of anatase TiO_2 nanocrystals is still unclear and under debate. In this work, a simple photoelectrochemical method was employed to meaningfully quantify the intrinsic photocatalytic activities of {001} and{101} faceted TiO_2 nanocrystal photoanodes. The effective surface areas of photoanodes with different facets were measured based on the monolayer adsorption of phthalic acid on TiO_2 photoanode surface by an ex situ photoelectrochemical method, which were used to normalize the photocurrents obtained from different faceted photoanodes for meaningful comparison of their photocatalytic activities. The results demonstrated that the {001} facets of anatase TiO_2 nanocrystals exhibited much better photocatalytic activity than that of {101} facets of anatase TiO_2 nanocrystals toward photocatalytic oxidation of water and organic compounds with different functional groups(e.g.,–OH, –CHO, –COOH). Furthermore, the instantaneous kinetic constants of photocatalytic oxidation of pre-adsorbates on {001} faceted anatase TiO_2 photoanode are obviously greater than those obtained at {101} faceted anatase TiO_2 photoanode, further verifying the higher photocatalytic activity of {001} facets of anatase TiO_2.This work provided a facile photoelectrochemical method to quantitatively determine the photocatalytic oxidation activity of specific exposed crystal facets of a photocatalyst, which would be helpful to uncover and meaningfully compare the intrinsic photocatalytic activities of different exposed crystal facets of a photocatalyst.