The XRD pattern of the as-prepared sample is shown in
Fig. 1a. It is seen that all diffraction peaks are well defined
and can be perfectly assigned to the anatase TiO2(JCPDS-21-1272). Other polymorphs such as rutile and brookite phases
were not observed, as indicated by the enlarged low-speed-scanned XRD pattern (inset ofFig. 1a). These results suggest
that the present sample is fully crystallized and highly phase-pure, which greatly differs from the recently reported water-soluble TiO2nanoparticles[11]because in the XRD spectrum
of the latter, a discernable shoulder peak attributed to the sec-ondary brookite phase appeared at 2θ of 30
◦
. From the peak
broadening, the average crystallite size of the as-prepared sam-ple was calculated to be around 7 nm. The corresponding TEM
images in Fig. 1b showed particle sizes in the range of 20–
40 nm, which are several times larger than those calculated by
XRD peak broadening, indicating a certain degree of agglomer-ation. From HRTEM image observation, the crystallite size of
the singular tiny crystals is also about 7 nm (inset of Fig. 1b).
The observed weak aggregates will be confirmed by the particle
size distribution (PSD) measurements.