Ultrathin defective heterojunction for visible light NO removal: correlation between microstructure and reaction mechanisms

Abstract

Successful integration of defective heterojunctions is a proven effective strategy for promoting carrier separations and strengthening 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 the unique layered structure of BiOCl, defective BiVO₄/BiOCl heterojunctions were designed and integrated. The 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 a more positive DeNO_x index (0.36) than their constituent monomers. The improved activities and stabilities of surface defects were further examined by multi-run NO removal and EPR. The NO conversion products were validated by in situ DRIFTS investigation, which 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 and massive production of active species by coupling 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.