Oxygen vacancies-modified S-scheme Bi₂Ti₂O₇/CaTiO₃heterojunction for highly efficient photocatalytic NO removal under visible light

Photocatalytic NO removal is limited by many factors, such as high recombination rate of photogenerated charge carriers and secondary pollution caused by incomplete oxidation. Here, S-scheme Bi2Ti2O7/CaTiO3 heterojunction composites with oxygen vacancies were prepared by solvothermal synthesis in conjunction with calcination. After Bi2Ti2O7/CaTiO3 calcined at 600 °C, the photocatalytic NO removal efficiency increases from 58% to 78% under visible light with the lowest production of intermediate NO2, where the initial concentration of NO was diluted to ca. 600 ppb by air stream and the flow rate was controlled at 1 L·min-1. The enhanced photocatalytic performance is attributed to the synergistic effect of S-scheme heterojunction structure and oxygen vacancy as evinced by ESR and XPS analysis. Active species trapping experiments suggest that photogenerated electrons, superoxide ions and holes are the main active species in the photocatalytic NO conversion. This study provides a reference for the design of highly efficient visible-light responsive photocatalyst by construction of S-scheme heterojunction and oxygen vacancy simultaneously.