Synergistic integration of metallic Bi and defects on BiOI: Enhanced photocatalytic NO removal and conversion pathway

Abstract

Surface plasmon resonance (SPR) of metals may provide a way to improve light absorption and utilization of semiconductors, achieving better solar light conversion and photocatalysis efficiency. This study uses the advantages of SPR in metallic Bi and artificial defects to cooperatively enhance the photocatalytic performance of BiOI. The catalysts were prepared by partial reduction of BiOI to form Bi@defective BiOI, which showed highly enhanced visible photocatalytic activity for NOx removal. The effects of reductant quantity on the photocatalytic performance of Bi@defective BiOI were investigated. The as-prepared photocatalyst (Bi/BiOI-2) using 2 mmol of reductant NaBH4 showed the most efficient visible light photocatalytic activity. This enhanced activity can be ascribed to the synergistic effects of metallic Bi and oxygen vacancies. The electrons from the valence band tend to accumulate at vacancy states; therefore, the increased charge density would cause the adsorbed oxygen to transform more easily into superoxide radicals and, further, into hydroxyl radicals. These radicals are the main active species that oxidize NO into final products. The SPR effect of elemental Bi enables the improvement of visible light absorption efficiency and the promotion of charge carrier separation, which are crucial factors in boosting photocatalysis. NO adsorption and reaction processes on Bi/BiOI-2 were dynamically monitored by in situ infrared spectroscopy (FT-IR). The Bi/BiOI photocatalysis mechanism co-mediated by elemental Bi and oxygen vacancies was proposed based on the analysis of intermediate products and DFT calculations. This present work could provide new insights into the design of high-performance photocatalysts and understanding of the photocatalysis reaction mechanism for air-purification applications.