Enhancing the near-infrared photocatalytic activity and upconversion luminescence of BiOCl:Yb3+–Er3+ nanosheets with polypyrrole in situ modification

Abstract

Photocatalytic behavior and upconversion (UC) luminescence of rare earth (RE) ions are two opposite photophysical processes; however, improving the ultimate light conversion efficiency, light absorption enhancement and suppression of excited state electronic recombination is identically crucial to both. In this work, we report an oxygen vacancy engineering strategy for BiOCl:Yb³⁺–Er³⁺ nanosheets by polypyrrole (PPY) in situ modification that connects the two photophysical processes, which may become an important aspect of expanding the application of near-infrared (NIR) light for photocatalysis. It is indicated that compared with unmodified samples, NIR and the visible light degradation of the rhodamine B (RhB) efficiencies of PPY-modified nanosheets were increased by 7.66 and 8.93 times, respectively; moreover, the UC emission of Er³⁺ ions under 980 nm excitation increased by 59 times. Experimental and DFT calculation results show that the oxygen vacancies (OVs) induced by PPY modification not only extend the absorption to the NIR regions by the construction of intermediate energy bands, but also promote the separation of photogenerated carriers of BiOCl nanosheets by enhancing the internal electric field (IEF). We showed that the energy ladder effect of the 4f–4f transitions of RE ion helps the intermediate energy bands to utilize NIR light to achieve more efficient photocatalysis; the extended decay rates of RE ion under the enhanced IEF are responsible for the much stronger UC emission at the same time. The results of this work exploring high-efficiency photocatalytic materials with NIR response is of great significance to further improve solar energy utilization efficiency and promote the development and application of photocatalytic technology.