3. Results and discussion
3.1. The function of surface treatment
Fig. 2 shows the XRD patterns of samples C1 and C2. For the
control sample C1 without PAA treatment, only the diffraction
peaks of magnetite were detected. There was a broad peak at
2h = 15–25 which has been considered as from the amorphous silica
[3]. We deduced that the TiO2 generated from TBOT was removed
by repeated washing with ethanol. It was clear that no
TiO2 has been attached without PAA treatment. However, the sample
C2 has both anatase titania and magnetite phases, as shown by
the characteristic peaks of titania and magnetite in Fig. 2. The characteristic
peaks of anatase TiO2 in sample C2 agreed well with the
standard anatase TiO2 XRD spectrum (PDF #71-1166). Using Scherrer’s
formula, the average crystal size of TiO2 could be estimated to
be about 15 nm. The above results indicate that modification on
the surface of silica introduced by PAA is quite important for the
deposition of titania. Meanwhile, calcination at 500 C was applied
to convert amorphous TiO2 into crystalline anatase titania to improve
the photocatalytic activity. It was noted that the phase of
magnetite well retained after calcination owing to the protection
of closely encapsulated silica shells.