The recombination of photo-generated charge in the strontium titanate (SrTiO₃) semiconductor occurs quickly, which limits the usage of this semiconductor for photocatalytic applications. Therefore, the coupling of copper oxide (CuO) on Strontium titanate can improve its photo-catalytic activity, which investigated in this study. The relocation and separation of photo-excited electron and hole between strontium titanate and copper oxide nanoparticles as semiconductors can partially describe the improvement of photocatalytic activities of SrTiO₃/CuO nanoparticles. Hence, photoluminescence technique and ultraviolet–visible diffuse-reflectance analysis were performed to investigate possible separation mechanisms. Furthermore, by using suitable scavengers, which cease the oxidation process, free radical paths were determined and then fitted with the most possible mechanism. According to the mechanism, the CuO could help to separate the photo-generated electron-hole, efficiently. To evaluate photocatalytic degradation characteristics of the nanoparticles, the efficacies of several factors such as reaction time, dosage of catalyst, CuO percentage, and pH were investigated in a batch reactor with an internal UV lamp. The response surface modeling (RSM) was used to optimize the effective factors. By considering the impressive ranges of the factors, 31 runs were designed using the four-factor-five-level central composite design (CCD). The optimum levels of the operational parameters were found at pH of 7.5, catalyst dosage of 1.15 g/L, reaction time of 6.2 h, and CuO percentage of 2.3. Regression analysis with an R² value of 0.987 showed a good agreement between the experimental outcomes and the predicted value with a removal of 100%.