Fig. 2. Size variations of the TiO2 nanoparticles in the presence of HA as a function of
time under a pH of 3.0 (a); 6.5 (b); and 9.0 (c). The gray domain denotes the adsorption
process of HA by TiO2 in darkness for 24 h, and the inset depicts the corresponding
variation in the zeta potential in the experimental process. The UV irradiation starts at
24 h and lasts for 12 h using two 9WUV lamps. The concentration of TiO2 is 20.0 mg/L;
the concentration of HA is 10.0 mg/L; and the ionic strength is 1.0 mmol/L.