Synthesis And Shape Controll Of Core@Shell Type Semicondutors Nanocomposites

The synthesis of CdS@TiO₂ core@shell type semiconductor nano-composites under the assist of ultrasonic irradiation is fully investigated, the photocatalytic properties of the composites were expected greatly enhanced in the visible region by designing the unique band structure of composites with TiO₂ nanocrystal "shell" loaded on the CdS "core". Also, another matter of this paper is focus on the synthesis of semiconductor nanocrystal with small band gap severed as a favorable "core" in the composites. Here numerous factors including temperature, organic surfactant, precursor, ratio of the reagents were taken into consideration in the carefully shape controlling of the lead sulfide nanocrystals.Two main parts were involved in the study: firstly the novel synthetical route of CdS@TiO2 was explored by introducing the ultrasonic irradication in aqueous system. Secondly, a series of PbS nanocrystal with attractive shape such as nanocube, nanowires, nanorods, nanobranchs were firstly prepared in the organic solvent with/without surfactant modification.Sonocehmical method was applied in the preparation of CdS@TiO2 core@shell type nano-composites. The thickness of TiO2 layer with clear interface and smooth surface was easily controlled by adjusting the sono-irradiaton time and the amount of precursor in contrast with other methods. Those nano-composites exhibit excellent photocatalyic property as been measured by degradation of MO in the visible light region, which is mainly due to the extending absorbance of the composites.Another important issue of this paper is discussing the formation of various shapes of PbS nanocrystals, which was rarely mentioned before. It is more charming to understanding the mechanism of formation anisotropic PbS nanocrystals(nanowires, nanorods, nanobranchs or superlattice) and isotropic nanocrystals(nanocube, nano-hexagonal). Heresystemic researches were carried out by adjusting the critical synthesis parameters including synthetical temperature, kinds of surfactant, ratio & amount of monomers, reaction time et ah it seems that the difference facets energy between {100} and {111} facets impacts a lot in the further shape evolvement, and the varied reaction temperature also changed those energy discriminatively.By changing the concentration and ratio of Tri-n-octylphosphine oxide(TOPO) oleic acid(OA), Dodecylamine(DOA) ,the shape of PbS nanocrystal varies tremendously, it may ascribe to the surfactant's propensity to the definite facets, for example, the TOPO is selective attachment to the (111) facets.As for the quantum dots synthesis under the organic solvent ,the control of process of nucleation and growth is of critical important, thus a ultra-short reaction time(²5 s) and rapid cooling is employed to get the nuclei without further growth, the nuclei posses 8 {lll}facets and 6 {100} facets, which is helpful to understand the shape evolvement.It was also exciting when superlattices composed of nanocube and nano-hexagonal as "Building Blocks" were formed when the reaction time lasted for more than 3 h. the coarse procedure of nanocrystals was explained by the attraction of dipole of nanocrystal generated along the [100] direction rather than Ostalwald ripening.