After the 24-h adsorption process, the intensities of all of the
fluorophores are relatively strong at a pH of 9.0, which are similar to
the results obtained for a pH of 6.5. The intensity of the humic-like
fluorophores decreases after 30 min of irradiation due to thephotocatalytic degradation of the HA. Meanwhile, the intensity of
the protein-like fluorophore increases slightly, similar to the results
obtained for a pH of 6.5. As the irradiation time increases, the
fulvic-like and protein-like fluorophores decrease gradually. In the
UV irradiation process, the particles aggregate to a larger size of
approximately 1200.0 nm after 4 h of UV irradiation, and all of the
fluorescence intensities areweaker compared to those at a pH of 3.0
and stronger than those at a pH of 6.5. It can be seen that the aggregation
size of the TiO2 nanoparticles in this case is greater than
that at a pH of 3.0 and smaller than that at a pH of 6.5, which indicates
that the aggregation size is proportional to the concentration
of photocatalytic degradation intermediates of HA by TiO2.
Overall, the aggregation of the TiO2 nanoparticles is caused by the
photocatalytic degradation of the HA. Therefore, the UV irradiation
played an important role in the stability of the nanoparticles
(especially photoactive nanoparticles) in an aquatic environment.