Mitigating the charge recombination by the targeted synthesis of Ag2WO4/Bi2Fe4O9 composite: The facile union of orthorhombic semiconductors towards efficient photocatalysis

Abstract The detrimental carrier recombination in semiconductors is a well-known bottleneck which limits their photocatalytic properties. This has led to intense research in understanding the mechanisms of carrier recombination as well as finding new ways to synthesize materials that offer efficient photocatalytic properties. Semiconductor-semiconductor heterojunctions have shown promise in this regard by providing a platform for separation of charges across the interface as well as the control over modifying the band alignment. Herein, we devise a two-step solution-based synthesis strategy to create a composite material between a wide band gap Ag2WO4 material and a narrow band gap Bi2Fe4O9 material. The Ag2WO4/Bi2Fe4O9 composite materials forms a type-2 heterojunction. The photocatalytic activity of the composite material was investigated by studying the degradation of Rhodamine-B dye in the presence of 3 wt%, 5 wt%, 7 wt%, and 9 wt% of Ag2WO4 in Bi2Fe4O9. The percentage degradation of Rhodamine-B in the presence of 7-Ag2WO4/Bi2Fe4O9 was found to be 87% in comparison to 80% in 3-, 83.4% in 5-, and 85% in 9-Ag2WO4/Bi2Fe4O9. The rate of degradation is nearly 10 times faster in 7-Ag2WO4/Bi2Fe4O9 as compared to pristine Bi2Fe4O9 and 4 times faster as compared to 3-Ag2WO4/Bi2Fe4O9. The materials also exhibit strong photostability with approximately 80.3% retention in photocatalytic efficiency after 4 initial catalytic cycles. This heterojunction owes its efficient photocatalytic activity to the peculiar band alignment of the constituent semiconductors which allows photoinduced electron transfer to occur across the interface. This phenomenon results in the separation of charges, which increases their lifetime long enough to initiate chemical transformation.