This research investigates the enhanced photocatalytic activity of cuprous oxide (Cu₂O) nanoparticles (NPs)-titanium dioxide (TiO₂) nanotube (NT) composites for air purification, focusing on the removal of volatile organic compounds (VOCs) and Escherichia coli (E. coli) bacteria under simulated sunny light. Cu₂O-NPs were successfully deposited onto TiO₂-NTs via the successive ionic layer adsorption and reaction method. The resulting p- and n-type semiconductor heterojunction nanocomposites were characterized using various techniques, including scanning electron microscopy, transmission electron microscopy, ultraviolet–visible-light spectroscopy, and chlorinated radicals. The photocatalytic activity was evaluated for different VOCs present in indoor air (butadione, chloroform, and butyraldehyde) in the presence of E. coli bacteria. The results showed that the Cu₂O-NPs/TiO₂-NTs composites exhibited enhanced photocatalytic activity compared to pure TiO₂-NTs. The Langmuir–Hinshelwood model was used to describe the degradation kinetics, revealing that Cu₂O loading and the nature of the target pollutant influence the photocatalytic efficiency. This study has also highlighted the role of chlorinated radicals in the degradation process, especially for chloroform. The degradation process of chloroform generated chlorine radicals, which not only contributed to the degradation of other VOCs, but also enhanced the overall oxidative capacity of the system. This synergistic effect was observed to accelerate pollutant removal and improve the antibacterial efficacy against E. coli. The Cu₂O-NPs/TiO₂-NTs composites demonstrated significant reusability and antibacterial properties, highlighting their potential for sustainable indoor air purification applications.