Fengqing Wu

Microwave absorptive behavior of ZnCo-substituted W-type Ba hexaferrite nanocrystalline composite material

ZnCo-substituted W-type barium hexagonal ferrite of the order of nanoscale is synthesized and investigated as microwave absorber. Based on a two-layer structure with the thickness of only 1 mm, a big reflection loss over broadband is obtained. The microwave absorptive mechanisms of nanocrystalline composite material are also discussed.

Photodegradation of rhodamine B under visible light by bimetal codoped TiO2 nanocrystals

In the search for efficient photocatalysts working under visible light, we have investigated the effect of metal ions (Bi/Co, Fe/Co) codoping on the photocatalytic activity of TiO(2) prepared by stearic acid gel method. UV-vis spectra revealed that doped Co enhanced the absorbency of TiO(2) under visible light, and Bi/Co codoped TiO(2) showed higher absorbance than Fe/Co codoped TiO(2). The photoreaction based on the prepared samples for photodegradation of 20mg/l rhodamine B solution was examined. The results showed that Fe(0.1%)/Co(0.4%) codoped TiO(2) had the highest photoactivity among all as-prepared samples under visible light, though less absorbency of visible light, indicating that the photoactivity not only benefits from absorbency but also relates to the cooperative effect of the two dopants.

Surface state studies of TiO2 nanoparticles and photocatalytic degradation of methyl orange in aqueous TiO2 dispersions

Abstract Nanocrystalline TiO2 is prepared using a stearic acid gel method. Their surface state is analyzed by means of X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of methyl orange in TiO2 suspension is investigated. The relationships between surface state and photocatalytic activity are discussed.

The sol?gel template synthesis of porous TiO2 for a high performance humidity sensor

This research develops a simple template assisted sol-gel process for preparing porous TiO2 for a high performance humidity sensor. Tetraethyl orthosilicate (TEOS) as a template was directly introduced into TiO2 sol formed by the hydrolysis and condensation of titanium alkoxide; the following calcination led to the formation of TiO2-SiO2 composite, and the selective removal of SiO2 by dilute HF solution led to the formation of porous structure in TiO2. The resulting porous TiO2-based sensor exhibits high sensitivity and linear response in the wide relative humidity (RH) range of 11%-95%, with an impedance variation of four orders of magnitude to humidity change. Moreover, it exhibits a rapid and highly reversible response characterized by a very small hysteresis of <1% RH and a short response-recovery time (5 s for adsorption and 8 s for desorption), and a 30-day stability test also confirms its long-term stability. Compared with pure TiO2 prepared by the conventional sol-gel method, our product shows remarkably improved performance and good prospect for a high performance humidity sensor. The complex impedance spectra were used to elucidate its humidity sensing mechanism in detail.

New compounds constructed from polyoxometalates and transition metal coordination complexes with lower positive charge

Five new hybrid compounds constructed from polyoxometalates and transition metal coordination complexes with lower positive charge: [PW11CuO39][Cu(bpy)2]5 (1), [BW12O40][Cu(bpy)2]5 (2) [BW12O40][Cu(Phen)2]3[Cu(Phen)(H2O)]2·2H2O (3), [SiW12O40][Cu(bpy)2]4 (4) and [PW12O40][Cu(bpy)2]4 (5) have been prepared and characterized by IR, UV-Vis, XPS, XRD and single crystal X-ray diffraction analyses. The packing motif of the [Cu(bpy)2]+ copper coordination complexes in compound 1 exhibits square supramolecular channels running along the a axis, which are then filled by the [PW11CuO39]5− ions. Compound 2 is isomorphours with compound 1. Compound 3 contains a novel 2-D supramolecular layer structure constructed from [Cu(Phen)2]+ copper coordination complexes through π⋯π interactions. The packing motif of the [Cu(bpy)2]+ copper coordination complexes in compound 4 exhibits a supramolecular channel which is different from compound 1. Compound 5 is isomorphours with compound 4.

Study on ethanol sensitivity of nanocrystalline La0.7Sr0.3FeO3-based gas sensor

Abstract La 0.7 Sr 0.3 FeO 3 nanocrystalline material was synthesized with citrate method, and an indirect-heating sensor was fabricated based on it. After measurement and analysis of its characteristics, this new kind of device showed us high sensitivity, selectivity and stability against disturbing gases, the response and recovery times of it was also found be much shorter than conventional devices.

Synthesis, Characterization and Humidity Sensitive Properties of Nanocrystalline LaCoxFe1–xO3

Abstract The nanocrystalline LaCo x Fe 1– x O 3 with different concentrations of Co was prepared by polyethylene glycol (PEG) sol-gel method and characterized by differential thermal analysis and thermal gravimetric analysis (DTA-TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM). It was found that the crystal structure of perovskite-type could be obtained at 600 °C, and the concentration of Co had significant effects on the solid-state reaction and the average particle size of the obtained nanocrystals. Furthermore, the humidity-sensitive properties of nanocrystalline LaCo x Fe 1– x O 3 were investigated, and it was found that LaCo 0.3 Fe 0.7 O 3 exhibited higher sensitivity to humidity compared with other samples. The addition of Na 2 CO 3 improved the humidity-sensitive properties of this sample, and made its response to humidity good in the whole humidity range of 11%–95% relative humidity (RH).

Electron behavior and photoelectric gas-sensitive characters of nanocrystalline La1−xSrxFeO3

Abstract Electron transport types and photovoltage gas-sensitive characters of nano-La1−xSrxFeO3 were probed by the vacuum adsorptive surface photovoltage technique. The results show that the band distortion and the increased anion vacancy caused by doping with a little Sr2+ ions in the nanomaterial are of advantage to form new exciton levels and the localized photogenic free charge carriers, to promote the separation of exciton pairs with increasing sensor gas pressure, and to increase quantum-optical efficiency as result of the effect of surface and quantum confinement.