engleski

Influence of synthesis route on the formation of ZnO particles and their morphologies

The formation and microstructure of ZnO particles, obtained by mixing concentrated aqueous Zn(NO3)2 and NaOH solutions, were monitored by XRD, FT-IR spectroscopy, FE SEM and B.E.T. techniques. At 160 oC and pH near 6, plate-like Zn5(OH)8(NO3)2(H2O)2 particles were formed at the beginning of precipitation process, then quickly transformed to ZnO via dissolution/reprecipitation mechanism. ZnO particles of different geometrical shapes, based on hexagonal prism, were produced. Precipitation at 20 oC and pH near 6 yielded plate-like Zn5(OH)8(NO3)2(H2O)2 particles which were present up to 6 months of ageing. Autoclaving of the precipitation system at 160 oC up to 72 h and pH near 7 yielded only ZnO particles as pseudospheres, hexagonal dipyramids and open form of hexagonal pyramid. All these particles were built from much smaller ZnO units. Only ZnO particles were obtained at 160 or 20 oC and pH near 13. All ZnO particles, thus obtained, were plate-like and their size depended on the temperature and time of ageing. B.E.T. measurements can be related with the geometrical shapes and size of ZnO particles, as inspected with FE SEM. FE SEM inspection did not show the formation of microporous ZnO particles. The geometrical shape of the corresponding FT-IR spectra can be also related with the geometrical shapes and size of ZnO particles.

ZnO; Zn5(OH)8(NO3)2(H2O)2; precipitation; XRD; FT-IR; FE-SEM; BET

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