Preparation Via Microemulsion Processing Route, Characterization And Studies On Properties For Bi₂O₃ And Bi₂Sn₂O₇ Powders

The dissertation reports the preparations of the Bi2O3 and Bi2Sn2O7 powders using the nanodroplets in the water-in-oil microemulsion containing aqueous solution, TX100, n-hexanol and cyclohexane as microscale reactors. The precursor and calcined particles are characterized by the measurements of TGA-DTA,XRD,TEM,IR etc. and some factors that affect the size and shape of the precursor particles are also discussed. For the Bi2O3 powders via microemulsion processing route, the photocatalytic properties are investigated.The main conclusions drawn from the research work are cited as follows:In the microemulsion medium, the as-prepared particles about 50nm in size for the Bi2O3 powders are prepared via the chemical reaction between Bi(NO3)3 and NH3·H2O. The α-Bi2O3 particles derived from the decomposition of precursor particles at 500℃ calcination temperature are 22.3nm in the average crystalline size. According to the results of BET specific surface area analysis, these α- Bi2O3 particles have as 4 to 5 fold specific surface area as those obtained via conventional hydrolysis processing route, and from the UV-Vis diffusively reflective absorption spectra, the maximum absorption peak for the former has been observed with a light shift towards higher wavenumbers than the latter. The photocatalytic results show that for the α-Bi2O3 powders with high specific surface area formed in the microemulsion system, the photocatalytic activity for degrading the dyes of methyl orange and rhodomine B has remarkably been enhanced.2. In the microemulsion medium, the Bi2Sn2O7 precursor particles are also obtained via the coprecipitation of Bi3+ and Sn4+ using NH3·H2O as the precipitant. The tetragonal phase Bi2Sn2O7 powders are formed via the decomposition of the precursor particles calcined at 500℃ temperature, with the average crystalline size of 10 nm and the spherical particle diameter in the range of 10-20nm.The IR spectrum shows that there is a shift towards lower wavenumbers for the band corresponding to the Sn-O stretching vibrations than those formed at over 600℃.3. According to the results of the TGA-DTA, XRD and IR analysis, during the decomposition of the precursor particles for Bi2O3 , one form of bismuth alkali nitrate is developed as an intermediate phase, which can be transformed into metastableβ-Bi2O3 from 307℃ to 480℃,during which the coordinate form for NO3- may be changed.4. Through the investigations of some factors which may have effects on the sizeand shape of precursor particles formed in microemulsion, we found that the content of aqueous solution had a significant influence on them.