Mechanical ball-milling preparation and superior photocatalytic NO elimination of Z-scheme Bi12SiO20-based heterojunctions with surface oxygen vacancies

The creation of n-p heterojunctions with surface oxygen vacancies (OVs) is significant to realize satisfactory photocatalytic performance, thanks to the effective regulation of interface carriers and amplified production of various reactive species. In this study, binary composites Bi12SiO20/Bi2S3 (BSO-XS) were in situ fabricated via a mechanical ball-milling protocol and subsequently characterized by a battery of analyses. Both anticipated components coexisted and were merged into n-p heterojunctions. Simultaneously, surface OVs were generated along with the decrease of particle size and vulcanization. These composites possessed dramatically strengthened photocatalytic NO annihilation with the diminished generation of NO2. After exposure to visible light for 4 min, the best candidate, BSO-0.3S, induced NO removal around 56% and NO2 formation below 3 ppb, superior to bare components and other composites. The combination of n-p heterojunctions and surface OVs contributed to augmented catalytic capacities through the enhanced visible-light absorption, efficient carriers redistribution and further boosted reactive oxygen-containing species such as center dot OH, center dot O-2(-), and O-1(2), the strong affinity of surface OVs to reactants of NO, O-2, and H2O, and favorable energy changes during oxidation reactions, which were sustained by analytical results and density-functional theory (DFT) calculations. A reaction pathway of NO elimination was deduced by in-situ DRIFTS spectra, and a preliminary photocatalysis mechanism was speculated in a Z-scheme model. Such work aims to realize the synergistic effect of Z-scheme n-Bi12SiO20/p-Bi2S3 hetero-junctions and surface OVs over the photocatalytic NO removal and thus provides suitable catalyst candidates for air pollutants removal.