Praparation And Performance For Lower-Dimension Nanometer Inorganic Materials With Hollow Structures

Among the many lower-dimension inorganic materials with distinct structural and geometrical features, freestanding hollow micro-, meso-, and nanostructures represent an important class of novel materials attracting special interest, due to their potential scale-dependent applications such as in photonic devices, drug delivery, active material encapsulation, ionic intercalation, surface functionalization, robust catalysts/carriers, and size-selective reactions. However, there has been only little progress in the synthesis of one-dimension noncircular nanotubes and zero-dimension metal hollow sphere, particularly in hollow silver spheres and rectangular nanotubes. Based on the current situation, we attempt some new methods to prepared hollow silver spheres and rectangular tungstic oxide nanotubes. The detail research contents and results are summarized as follows:(1) Monodisperse hollow silver spheres were synthesized by using phase-change emulsion as template. The preceeding state of this template could be obtained via simple emulsification like the soft-template method, and then the oil-phase (here we select beeswax) underwent coagulation process to achieve a kind of hard-template under ultrasonic treatment. It is proposed that AgBr "seeds" (precursor of silver nanoparticle) here performed a role of Pickering emulsifier. They successfully cooperated with CTAB molecules to stabilize the emulsions during the phase transition. The mean diameter of the resultant AgBr-coated solid emulsion beads is 160.5nm and the polydispersity index is 1.046. AgBr "seeds" were sequently reduced to form silver particles just like in the standard photographic procedure. When more silver nitrate solution was added, primary silver particles make silver ions around them initiated catalytic reduction until the integrated silver shell was completed. The silver wall-thickness can be conveniently modulated through change the content of AgNO₃. Our results show that not only is this approach simple but also the removal of the template is high efficient since beeswax is a aggregate of multiple small molecules which are easily transfer from inside to outside. Moreover, the natural beeswax template can be recycled, so the whole process is environmentally friendly.(2) We prepare rectangular WO₃.H₂O nanotubes by the aid of intercalated PANI. Firstly, as compared to conventional synthetic process of intercalated materials, the oxidative polymerization of aniline and the intercalation of nanosheets formed at the same time along with concomitant ion exchange by means of double-emulsion method. We choose the resultant uniform nanosheets as precusor followed by continuous stirring for six days at 60℃. According to different morphologies we observed at different reaction time stage, we found PNAI-intercalated WO₃.H₂O nanosheets rolling into nanotubes. Furthermore, we also found the corresponding interlayer distances of WO₃.H₂O layers decreases as the reaction time is increased. FTIR data indicates that the degree of in-situ oxidation of PANI increased with increasing reaction time. At the same time, UV/Vis-near IR monitors polymer conformational change between layers. So the decreases of interlayer distances depicted in XRD could not be ascribed to water loss or emigration of PANI from a kinetic point of view but to change of configuration in PANI under oxidation. Further, this change in cross-sectional area and arrangement of PANI also bring out curling movement of WO₃.H₂O layers. The uniqueness of this method is that not only the preparation is made under a relatively mild condition, but also the nanosheets directly roll into rectangular cross-sectional nanotubes without suffering nanoscrolls stage.The reciprocal magnetic susceptibility of PANI-intercalated WO₃.H₂O nanotubes rapidly decreased from positive to negative at 90k, which endowed them with potential material for electromagnetic device.