RSC Adv., 2015,5,90991

New insights into self-modification of mesoporous
titania nanoparticles for enhanced photoactivity:
effect of microwave power density on formation of
oxygen vacancies and Ti3+ defects

Mesoporous titania nanoparticles (MTN) were successfully prepared by a microwave (MW)-assistedmethod
under various power densities. The catalysts were characterized by XRD, FT-IR, surface area analysis, TEM,
and ESR. The characterization data indicated that higher power density increased the crystallinity and
surface area of the MTN while decreasing the particle size and band-gap energy of the TiO2.
Significantly, MW heating played an important role in formation of oxygen vacancies (OV) and Ti3+ site
defects (TSD). The MTN (T1–T3) with 0.12, 0.37, and 0.56 W g1 power density were found to degrade
84%, 88%, and 96% of 2-chlorophenol (2-CP) under visible light, respectively, compared to 69% by
commercial TiO2. Besides narrowing the band gap, the OV and TSD also acted as electron acceptors
that hindered the electron–hole recombination, as well as facilitated the charge carrier migration. The
kinetics study over T3 showed that adsorption was the controlling step in the 2-CP degradation, which
followed a pseudo-first-order Langmuir–Hinshelwood model. The photocatalytic reaction was still
stable, even after five cycle runs without severe catalyst deactivation. This study demonstrates that the
uniform heat distribution provided by MW is able to produce MTN that are rich with OV and TSD that are
effective under visible light irradiation.