Defect and charge transfer efficiency of nano-photocatalysts are important factors which influence their photocatalytic performance.In this work,oxygen vacancies are successfully introduced in the synthesis process of Bi2Al4O9/β-Bi2O3 heterojunctions through one-step in situ self-combustion method.High-resolution transmission electron microscopy (HRTEM),UV-Vis diffuse reflectance spectra (UV-Vis DRS),and electron spin resonance (ESR) measurements confirm the existence of oxygen vacancies.In addition,by controlling the ratio of reactants of Bi(NO3)3 to Al(NO3)3,the ratio of Bi2Al4O9 and β-Bi2O3 in the heterojunction can be easily adjusted.Photocurrent responses and surface photovoltage spectroscopy (SPV) indicate that the construction of the Bi2Al4O9/β-Bi2O3 heterostructure improves the separation efficiency of the photo-generated electrons and holes.CO2-TPD results imply that the amounts and stability of heterojunctions are enhanced compared with their counterparts.The Bi2Al4O9/β-Bi2O3 heterojunction with 14 mol％ Bi2Al4O9 shows the highest photocatalytic ability for reduction of CO2 into CO.The enhanced photoreduction of CO2 performance can be ascribed to the synergistic effects of the heterojunction for electron sep-aration and oxygen vacancies for CO2 activation.