This study investigates the enhancement of photocatalytic activity in Cu₂O/TiO₂ heterojunctions by creating oxygen vacancies. The heterojunctions were synthesized using a one-step method by varying the amounts of ethylenediaminetetraacetic acid (EDTA), sodium citrate, and copper acetate. The optimal Cu mass fraction for the heterojunction was found to be between 0.075% and 0.55%, with the highest CO yield of 10.22 μmol g⁻¹ h⁻¹. High-resolution transmission electron microscopy and electron paramagnetic resonance studies confirmed the presence of optimal oxygen vacancies in the most effective heterojunction. Density functional theory (DFT) calculations showed that the energy barrier for *CO₂ to *COOH conversion in Cu₂O/TiO₂ with oxygen vacancies is 0.088 eV lower than in TiO₂, indicating enhanced photocatalytic activity. The study also demonstrated the stability and reproducibility of the catalyst, making it a promising material for CO₂ reduction applications.This study investigates the enhancement of photocatalytic activity in Cu₂O/TiO₂ heterojunctions by creating oxygen vacancies. The heterojunctions were synthesized using a one-step method by varying the amounts of ethylenediaminetetraacetic acid (EDTA), sodium citrate, and copper acetate. The optimal Cu mass fraction for the heterojunction was found to be between 0.075% and 0.55%, with the highest CO yield of 10.22 μmol g⁻¹ h⁻¹. High-resolution transmission electron microscopy and electron paramagnetic resonance studies confirmed the presence of optimal oxygen vacancies in the most effective heterojunction. Density functional theory (DFT) calculations showed that the energy barrier for *CO₂ to *COOH conversion in Cu₂O/TiO₂ with oxygen vacancies is 0.088 eV lower than in TiO₂, indicating enhanced photocatalytic activity. The study also demonstrated the stability and reproducibility of the catalyst, making it a promising material for CO₂ reduction applications.