Despite significant advancements in the improvement of heterogeneous photocatalysis towards water treatment, these processes still have some bottlenecks. In this research paper, oxygen vacancy richTiO(2) was combined with Bi4O5Br2 nanoparticles (denoted as TiO2-OVs/Bi4O5Br2) by eco-friendly hydrothermal approach. The outcomes demonstrated that the photoactivity strongly depends on plenteous active sites, reinforced charge segregation, as well as striking visible-light absorption ability in TiO2-OVs/Bi4O5Br2 nanocomposite with n-n heterojunction. The photoactivity was found to follow the trend: TiO2-OVs/Bi4O5Br2 (30%) > TiO2-OVs > TiO2. Briefly, the removal efficiencies of RhB, MB, and fuchsine were 100%, 96.2%, and 84.7% using TiO2-OVs/Bi4O5Br2 (30%) in 120 min, while they were 25.1%, 20.0%, and 15.3% over the TiO2, respectively. Further, the boosted rate constant was observed for the photoreduction of Cr (VI) on the TiO2-OVs/Bi4O5Br2 (30%) nanocomposite, which was 19.4 and 7.8-folds more than the TiO2 and TiO2-OVs photocatalysts, respectively. The radical scavenging tests with different quenchers demonstrated that holes and superoxide anion radicals take part in the degradation reaction. Finally, by investigating the electrochemical properties, a mechanism was offered to describe the improved e-/h+ pairs separation and migration. This research displayed that the design of n-n heterojunction using TiO2-OVs could be suitable for severely improving photocatalytic performance of TiO2 under visible light. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.