Enhanced photocatalytic NO removal with the superior selectivity for NO2−/NO3− species of Bi12GeO20-based composites via a ball-milling treatment: Synergetic effect of surface oxygen vacancies and n-p heterojunctions

Bi12GeO20-based composites Bi12GeO20-Bi2S3 (BGS) were successfully constructed through a facile ball-milling method using sulfur powder for the first time. Systematical analyses verified the in-situ generation of n-p heterojunctions with surface oxygen vacancies (OVs). These composites showed reinforced photocatalytic removal of NO at ppb level under visible light with high selectivity for NO2−/NO3− species, avoiding the generation of toxic NO2 as far as possible. Especially, the best candidate BGS0.1 possessed 46% NO removal with 96% selectivity for NO2−/NO3− species that were much higher than those by Bi12GeO20, mainly relevant to the enhanced visible-light absorption, synergistic effect of heterojunctions containing surface OVs to promote charge carriers segregation and reactive radicals formation, and suitable phase composition with proper band structures. The effect of heterojunctions with surface OVs over band structures and reaction paths was demonstrated by density functional theory (DFT) calculation. DRIFTS and FT-IR spectra were recorded to deduce NO conversion routes. Eventually, a preliminary photocatalysis mechanism of these robust composites was conjectured in a Z-scheme manner basing experimental and analytical results. This study might pave roads for in-situ construction of sillenite-based composites with surface OVs by a mechanochemical approach with satisfactory photocatalytic NO treatment under visible light.