Key Engineering Materials Vols. 336-338

Abstract: The principle of melt-phase separation process for preparation of nanoparticle TiO2 is based on the adjustment of glass phase-separation structure. TiO2 grain size can be controlled by changing heat treatment temperature. The sample was composed of Na2O-B2O3-SiO2-TiO2 glass system (melted at 1573K). A photocatalytic nanoparticle TiO2 which was loaded on porous glass can be obtained by heat treatment of glass system at various temperatures and then acid washing. The results have shown that the glass phase-separation structure size matches crystallization rate and an optimal photodegradation property of TiO2 is achieved. It was found that the suitable heat treatment condition was at 848K for 12h, although its performance slightly changes with the composition variations.

Abstract: Nanometer CeO2 with the mean size of 15 nm is prepared by sol-gel method, and the CO catalytic oxidation activity of Pd-Cu catalysts with three kinds of CeO2 supports was studied. The results show that nanometer CeO2 supported Pd-Cu catalyst gives highest activity for CO oxidation. It can maintain CO complete conversion at about 40°C.

Abstract: The catalysts based on V/K/Ca and V/Ks/Ce systems for diesel soot catalytic oxidation were synthesized onto the porous alumina substrates. Both catalyst systems showed a good catalytic oxidation activity. The V/K/Ca system exhibited the lowest oxidation onset temperature (OOT) of about 359oC with a composition of V/K/Ca =1:1:0.1 where the V and Ca and/or K elements could form a kind of amorphous phase that determined the catalytic activity. The V/Ks/Ce system displayed the lowest OOT of about 350oC with a composition of V/Ks/Ce = 1:2:0.1 where the K2SO4 and K5V2O3(SO4)4 phases could contribute most to the catalytic activity.

Abstract: A sol-gel process was used to synthesize nanosized Ca-Zn ferrite powders. DTA-TG, XRD and SEM techniques are employed to investigate the thermal decomposition of the dry gel, phase composition and microstructure of nanosized ferrite particles. The results revealed that the Ca0.4Zn0.6Fe2O4 phase appeared while calcined the gel powders at 300 °C for 2 hrs, and the Ca0.4Zn0.6Fe2O4 crystalline can be formed completely at 400 °C. Hysteresis loop indicated that the nanocrystallites size has great influence on the magnetic properties, which leads to the increase of the specific saturation magnetization and the decrease in coercivity of the samples with increasing the particle size.

Abstract: Rare earth Yb-doped bismuth titanate Bi4-xYbxTi3O12 (BYT) nanocrystalline powders were obtained by a modified sol-gel method. TG-DTA, FI-IR and XRD were used to determine the lowest heat treatment temperature. Phase changes in the formation of BYT crystalline powders were discussed by XRD. The effect of Yb3+ cation substitution for Bi3+ cation on the microstructure of BYT was also developed with XRD. The grain size of BYT nanopowders is about 40 nm determined by TEM.

Abstract: Nanosized Ce0.8Gd0.05Y0.15O1.9 powders were synthesized using glycine nitrate process for use as the electrolyte of intermediate temperature solid oxide fuel cells. The powders were characterized by simultaneous thermogravimetry analysis (TGA) and differential thermal analysis (DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD pattern indicated that the powders exhibited a single phase with cubic fluorite structure. The TEM studies showed that the calcined powders exhibited an almost spherical morphology and the mean size of the particles was 30nm, which is in agreement with the calculated result of XRD.

Abstract: Nano-scaled particle of anatase phase titanium oxide was obtained from the conversion of ammonium oxotrifluorotitanate by thermal treatment in oxygen. The crystal of ammonium oxofluorotitanate was grown on glass at 40oC with an aqueous solution of ammonium hexafluorotitanate and boric acid. The titanium oxide was obtained from the conversion of ammonium oxotrifluorotitanate by thermal treatment in oxygen. The size of nano-scaled anatase titanium oxide increases with the temperature of thermal treatment, and the size distribution is from 10 to 30 nm corresponding to the thermal temperature from 300 to 1000oC. The photocatalytic activity of the nano-scaled titanium oxide was demonstrated by the photo-deposition of copper in the solution of copper nitrate and sodium oxalate. The photocatalytic activity for the sample treated thermally at 800 oC is 1.3 times higher than that of commercial P-25.

Abstract: The effect of ultrasonic treatment under low frequency and power condition on the surface adsorption state and photocatalysis activity of nanosized TiO2 photocatalyst was studied. Results obtained from UV-Vis absorption spectra revealed that obvious differences of adsorption state on TiO2 powder surface were found after ultrasonic treatment, which agreed with the DTA-TG results that the thermal peaks varied with increasing ultrasonic treatment time. Furthermore, the photocatalysis activity for methyl-orange solution under visible light irradiation (≥450 nm) varied in a similar way with increasing ultrasonic treatment time. Present study revealed that the ultrasonic treatment was an effective way to study the relation between the surface adsorption state and photocatalysis activity of present nanosize TiO2 photocatalyst.

Abstract: Precursor of nanosized TiO2 was prepared by alkoxide hydrolysis method. It was dried by common drying, far infrared drying, vacuum drying and supercritical drying before heat-treated at 600°C and 800°C. Influence of drying process and treatment temperature on the crystalline phase composition and photocatalytic activity were analyzed. The photocatalytic activity of the TiO2 dried by common and far infrared drying is higher than that of the TiO2 dried by vacuum and supercritical drying after treated at 600°C. The photocatalytic activity of the TiO2 dried by common and far infrared drying is lower than that of the TiO2 treated by the other two drying methods after treated at 800°C.

Abstract: Nanosize anatase TiO2 powders have been synthesized by hydrothermal synthesis by using technical grade TiOSO4 as precursor and urea as precipitating agent. The initial pressure of the reaction system was set at 6 MPa. Stirring speed was fixed at 300r/min. The reaction system reacted at the temperature ranged from 110 to 150°C for holding 2hrs to 8hrs and the concentration of the precursor was ranged from 0.25M to1.5M. XRD patterns show that the synthesized powders are in the form of anatase phase. Calculated grain size is ranged from 6.7 to 8.9nm by Scherrer method from the line broadening of the (101) diffraction peak of anatase. The specific surface area of the powders synthesized under different conditions is ranged from 124 to 240m2/g. The grain size of the powders increases with the increase of the reaction temperature, holding time and precursor concentration, respectively. The specific surface area decreases with the increase of reaction temperature and holding time, and does not obviously change with the change of precursor concentration when the concentration of the precursor is less than 1M. However, when the concentration is higher than 1M, the specific surface area will decrease quickly with the increase of the precursor concentration. XRD and DSC-TG analysis shows that the synthesized anatase TiO2 will begin to transform to rutile TiO2 at about 840°C. When heated to 1000°C for holding 1h, the anatase powders will transform to rutile completely.