Fig. S3 illustrates the removal of HA from the solution, which is
determined by the UVevis spectrophotometer at 254 nm. After 4 h
of irradiation, we observe that the percent of HA removed is
approximately 56.0% for a pH of 3.0; the percent of HA removed for
pH levels of 6.5 and 9.0 are nearly the same (nearly 100%). A neutraland alkaline pH is more favorable for the generation of $OH via hole
oxidation of OH or hydroxy on the surface of the TiO2. Therefore, it
may cause a more efficient attack of the HA molecules, which are
adsorbed on the surface of the TiO2. However, the acidic functional
groups become less protonated, and the molecule begins to uncoil
as the pH increases. Hence, it becomes easier for the HA molecules
to be attacked by $OH (Liu et al., 2008). Palmer (Palmer et al., 2002)
determined that the HA molecules transformed into micelles at low
pH levels, which was considered to be undesirable in thephotodegradation process. Compared with the results on the size,
we determined that the equilibrium time of the HA removal is in
accordance with the change in particle time of. This result verifies
that the photocatalytic degradation of HA dominates the aggregation
behavior of TiO2 in our study.