We studied the aggregation of photoactive nano-TiO2 under UV
irradiation in an aquatic environment. In the aquatic system, HA
would increase the stability of the nanoparticles via electrostatic
repulsion and steric hindrance. The HA possessed a strong negative
charge in the current pH range, which decreased the zeta potential
of the particles and increased the electrostatic repulsion between
the particles. The DLVO theory verified that the addition of HA
increased the net energy barriers and inhibited the aggregation of
the particles. Because light is ubiquitous in the environment, the
photoactive nano-TiO2 absorbed UV light could change their stability
in the aquatic system. In our study, we determined that the
photocatalytic degradation of the HA caused the behavior of the
nano-TiO2 to change. The removal of the HAwas in accordance with
the TiO2 aggregation time. Furthermore, the results illustrated that
the UV light had different effects on the aggregation and stabilization
of the nano-TiO2 under different pH levels. It is determined
that the aggregation size is proportional to the concentrations of
photocatalytic degradation intermediates of the HA by the TiO2.
Under neutral and alkaline conditions, more HA was degraded and
fewer intermediates were generated. Therefore, larger aggregation
sizes under neutral and alkaline conditions were exhibited. Based
on the results, we could remove the nano-TiO2 in the aquatic system
by adjusting the UV irradiation time and pH in the water.