A new route for the preparation of nanocrystalline TiO2 particles based on the pH swing method assisted by ultrasonic irradiation in the presence of a surfactant (Pluronic P-123) has been successfully achieved. The prepared TiO2 catalysts were calcined from 400 to 800 degrees C and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infra-red spectroscopy (FTIR), gas adsorption measurements (BET) and thermogravimetirc measurements (TAG/DTA) analyses. Characterization results revealed that the enhancement in the particle size of TiO2 by the pH swing method could be controlled by combining the pH swing with ultrasonic irradiation. Increasing the calcination temperatures led to an increase in both the particle and pore size, whereas the surface area and pore volume gradually decreased. A synergistic effect was observed in the combined process of pH swing with ultrasonication, yielding small TiO2 particles as well as high surface area, pore volume, pore diameter, and crystalline anatase phase. The activity of the catalysts was investigated for the oxidation of 4-chlorophenol (4-CP). TiO2 prepared with 15 times pH swing and calcined at 700 degrees C was found to show the highest rate for the oxidative degradation of 4-CP when compared to the TiO2 sample prepared with just 1 time pH swing and to the commercial P-25 TiO2 Degussa photocatalyst. Thus, a novel approach in controlling the various physico-chemical parameters of TiO2 nanoparticles was developed.