Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@gamma-Fe2O3) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and gamma-Fe2O3 effectively reduced the catalyst band gap (E-g), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@gamma-Fe2O3/PDS and vis-gamma-Fe2O3/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe3+. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both (OH)-O-center dot and SO4 center dot were generated in the reaction system, while (OH)-O-center dot was relatively more dominant than SO4 center dot for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@gamma-Fe2O3/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from gamma-Fe2O3, causing efficient interfacial generation of surface-bond Fe2+ and reduction of adsorbed Fe3+. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX. (C) 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.