A novel Fe₂O₃@CeO₂ heterojunction substrate with high surface-enhanced Raman scattering performance

Surface-enhanced Raman scattering (SERS) has been applied in many fields due to its advantages of fast and nondestructive detection. For semiconductors, the large-scale electron-hole pair separation of heterojunction is conducive to efficient charge transfer, which is a promising SERS substrate. Here, we designed a Fe₂O₃@CeO₂ heterojunction substrate by hydrothermal method and explored its enhancement mechanism in detail. α-Fe₂O₃ is a promising semiconductor with a narrow bandgap, and CeO₂ has adequate oxygen vacancies on the surface. Combing α-Fe₂O₃ and CeO₂ into a shell-core structure, Fe₂O₃@CeO₂ heterojunction presents higher SERS performance than pure Fe₂O₃ and CeO₂ for methyl orange (MO) molecule with a limit of detection (LOD) of 5 × 10⁻⁸ mol/L. Under the excitation of 514 nm, Fe₂O₃ can produce an effective exciton resonance due to its narrow bandgap (2.01 eV). The oxygen vacancy in CeO₂ acts as the active site to promote the adsorption of molecules and facilitate the photo-induced charge transfer (PICT) between the substrate and MO molecules. Therefore, the high SERS performance of Fe₂O₃@CeO₂ heterojunction is achieved due to the coupling effect of excitons resonance, molecular resonance, and PICT resonance. It is found that Fe₂O₃@CeO₂ has good SERS performance and stability to organic pesticides, especially metamitron (LOD = 5 × 10⁻⁹ mol/L). This work combines the advantages of Fe₂O₃ being prone to producing photoelectrons and abundant oxygen vacancies of CeO₂, providing a reference for designing semiconductor SERS.