illustrates the typical TEM image of the assynthesized
Bi2O3 product when the concentration of Bi(NO3)3
was 0.5 mol L−1 and the reaction was kept at 100 ◦C for 2 h. It
is obvious that the product consists of well-dispersed spherical
nanoparticles with a mean diameter of 67 nm. Agglomeration
was hardly found in this sample, although it has a wide range of
particle size distribution varying from 10 to 130 nm as revealed
in Fig. 2(e). Inset of Fig. 2(a) shows the selected area electron
Fig. 1. Typical XRD pattern of the as-synthesized Bi2O3 nanoparticles.
diffraction (SAED) pattern of single nanosphere as labeled in
Fig. 2(a). The bright and disorder SAED rings demonstrate that
the as-obtained Bi2O3 nanoparticles are well-crystallized and
polycrystalline. Further investigations suggested that preparative
parameters, such as reaction temperature, reaction time,
reactant and dispersant concentration play significant roles in
determining the particle size and size distribution of the assynthesized
Bi2O3 nanoparticles. For instance, when all factors
were kept constant except that the concentration of Bi(NO3)3
was reduced from 0.5 to 0.02 mol L−1 and the reaction temperature
reduced from 100 to 90 ◦C, average grain size of the
as-synthesized Bi2O3 nanoparticles was decreased from 67 to
63 nm and there was no evident improvement in the particle
dispersity as indicated in Fig. 2(b) and (f). However, when
the concentration of Bi(NO3)3 was fixed at 0.5 mol L−1 and
the reaction was kept at 90 ◦C for 2 h, the as-produced Bi2O3
nanospheres were nearly monodisperse with a mean crystal size
of 60 nm as can be seen from Fig. 2(c) and (g). Most importantly,
the Bi2O3 nanoparticles can be re-dispersed in ethylene
glycol to form a colloids which can be stable up to 6 months in
ambient atmosphere conditions without any significant changes
in the particle shape, size and size distribution [see Fig. 2(d) and
(h)].
It was