Photoinduced formation of reactive oxygen species and electrons from metal oxide–silica nanocomposite: An EPR spin-trapping study

Metal oxide nanocomposites with photocatalytic activity have the potential for many applications in environmental remediation and biomedicine. In this study, we investigated the formation and stabilization of electrons/holes from three metal oxide–silica nanocomposites (CuO–SiO 2 , Fe 2 O 3 –SiO 2 and ZnO–SiO 2 ) under irradiation by electron paramagnetic resonance (EPR) technology. The characteristic EPR signals with g   =   2.00070–2.00105, Δ H p-p   =   2.17–2.37   G were determined, which corresponded to lattice-trapped electrons. Moreover, the generation of active species from CuO–SiO 2 , Fe 2 O 3 –SiO 2 and ZnO–SiO 2 in aqueous solution under irradiation was also systematically studied. The results showed that all the three nanocomposites could generate hydroxyl radical, singlet oxygen and electron. CuO–SiO 2 was more effective than Fe 2 O 3 –SiO 2 and ZnO–SiO 2 in producing hydroxyl radical and electrons, while ZnO–SiO 2 was the most efficient in generating singlet oxygen. In addition, CuO–SiO 2 exhibited most obviously photocatalytic activity toward degradation of bisphenol A, followed by Fe 2 O 3 –SiO 2 and ZnO–SiO 2 . These findings will provide vital insights into photocatalytic mechanisms and potentially photoinduced toxicity of metal oxide–silica nanocomposites.