C–N–S–tri doped TiO2 anatase phase was synthesized using a facile, effective and novel sonochemical method at low frequency (20 kHz) and at room temperature. Titanium butoxide as the titanium precursor and thiourea as the dopant source were used in the synthesis of the photo-catalyst. The effects of important parameters such as thiourea/Ti molar ratio, ultrasound intensity, sonication time and temperature were studied on the synthesis of tri-doped TiO2. The XPS results confirmed the presence of N, S, and C in the photo-catalyst. The photo-catalytic efficiency of the synthesized catalyst was studied toward the removal of Diclofenac as a model pharmaceutical organic pollutant. The results confirmed that the photo-catalyst synthesized with narrower band gap energy, shorter sonication time and higher ultrasound intensity leads to a rapid removal of Diclofenac. The effect of operational variables on the photo-catalytic activity of C–N–S tri doped TiO2 nanoparticles was studied and optimized using the Taguchi method as a statistical technique. Additionally, the degradation process followed the pseudofirst- order kinetics model and the highest apparent rate constant of 0.0632 min
1 achieved in 90 min. Chemical oxygen demand (COD) analysis confirmed that the mineralization took place completely (100%) under the optimized conditions in 180 min. Different scavengers were applied during the degradation process and active species such as
OH and O2

had key roles in the photo-catalytic process.

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