The photocatalytic performances of the three Fe3O4/SiO2/TiO2
composites are shown in Fig. 8b, with commercial P25 as a comparison.
The decrease of the RhB concentration over the photocatalyst
depends on two factors, i.e., adsorption and photodegradation
[35]. It is found that RhB degradation takes place even in the absence
of light, resulting from the adsorption by catalyst. In our
tests, sample C3 displays strongest capability to adsorb RhB among
them. However, its catalytic activity is rather low. Sample C2 has
the best photocatalytic activity to degrade RhB under UV irradiation
in the composites, showing a removal of RhB by more than
60%, due to its high loading of TiO2. However, the commercial photocatalyst
P25 exhibited much higher photocatalytic efficiency,
above 90% conversion after 60 min under UV light. We expect that
high active Fe3O4/SiO2/TiO2 composite can be obtained by repeated
PAA treatment followed by deposition of TiO2 nanoparticles to increase
the loading and surface area of TiO2. Further work on this
topic is in progress.