Green energy production is becoming increasingly important in mitigating the effects of climate change, and the photocatalytic approach could be a potential solution. However, the main barriers to its commercialization are ineffective catalysis due to recombination, poor optical absorption, and sluggish carrier migration. Here, we fabricated a two-dimensional (2D) reduced niobium oxide photocatalyst synthesized by an in situ thermal method followed by copper incorporation. Compared to its counterparts, pure Nb2O5 (0.092 mmol g-1 CO) and r-Nb2O5 (0.216 mmol g-1 CO), the strongly bonded Cu/r-Nb2O5 (0.908 mmol g-1) sample produced an exceptional amount of CO. The separation of charge carriers and efficient use of light resulted in a remarkable photocatalytic performance. The acceptor levels were created by the Cu nanophase, and the carrier trapping states were created by the oxygen vacancies. This mechanism was supported by ESR and DRIFT analyses, which showed that enough free radicals were produced. This study opens up new possibilities for developing efficient photocatalysts that will generate green fuel.