Ultrathin Defective Heterojunction for Visible Light NO Removal: Correlation between Microstructure and Reaction Mechanisms

Successful integration of defective heterojunction is a proven effective strategy to promote carrier separations and strengthen surface-interface redox reactions. Dipole moment variations are beneficial for charge carrier separation due to enlarged polarizations especially within defective ones. Herein, motivated by the dipole variations in BiVO4 and a unique layered structure of BiOCl, defective BiVO4/BiOCl heterojunctions were designed and integrated. As-integrated samples displayed unique nanosheets with thicknesses decreasing from 7.24 to 2.77 nm, resulting in the simultaneous formation of stable surface defects. The heterojunctions were investigated for the removal of dilute NO (~ ppb) under visible light and exhibited 1.85 and 2.05 folds enhanced efficiencies (75%), synchronous inhibition of NO2 (16.7% selectivity) and more positive DeNOx index (0.36) than their composed monomers, respectively. The improved activities and stabilities of surface defects were further examined by muti-run NO removal and EPR. The NO conversion products were validated by in-situ DRIFTS investigation that showed remarkable NO oxidation into NO3− and synchronous NO2 inhibition in thinner defective BiVO4/BiOCl. Mechanistic investigations indicated that surface defects in heterojunctions not only contributed to the improved light absorption, massive production of active species by coupling the suitable band alignments, prolonging the carrier lifetime (3.55 ns to 7.52 ns), but also facilitated strong interfacial electric field contact at the junction interface of monomers, which enabled the construction of a direct Z-scheme charge transfer mechanism for NO removal.