Visible-light-driven N-(BiO) ₂ CO ₃ /Graphene oxide composites with improved photocatalytic activity and selectivity for NO _x removal

N-doped (BiO) ₂ CO ₃ (NBOC)/graphene oxide (GO) composite obtained from three-dimensional hierarchical microspheres is successfully synthesized by one-pot hydrothermal method for the first time. In this synthesis, citrate ion plays a critical role in N doping. The obtained samples are used to degrade gaseous nitrogen oxides (NO _x ) at parts-per-billion (ppb) level under visible-light irradiation. NBOC–GO composite with 1.0 wt% graphene oxide (GO) displays the highest photocatalytic NO removal efficiency, which is 4.3 times higher than that of pristine (BiO) ₂ CO ₃ . Moreover, NBOC–GO composite significantly inhibits toxic NO ₂ intermediate production, indicating its high selectivity for NO conversion. Compared with regular GO, N doping considerably improves the catalytic performance of NBOC–GO composite, which increases NO removal by 74.6% and fully inhibits NO ₂ generation. The improved photocatalytic activity is mainly ascribed to extended optical absorption ability and enhanced separation efficiency of photogenerated charge carriers over NBOC–GO composite. Both results of electron spin resonance and theoretical analysis of band structure indicate that NO removal is dominated by oxidation with [rad]OH and [rad]O ₂ ⁻ radicals. The photocatalytic activity improvement mechanism over the NBOC–GO composite is proposed accordingly based on systematic characterizations. This study demonstrates a feasible route to fabricating Bi-containing composites with high selectivity and stability for air pollution control and provides a new insight into the associated photocatalytic mechanisms.