Enhancement of Fe2+/Fe3+ cycles by the synergistic effect between photocatalytic and co-catalytic of ZnxCd1-xS on photo-Fenton system

The exploration of new catalysts or co-catalysts to promoting the circulation efficiency between Fe3+ and Fe2+ in photo-Fenton system is of great significance for sewage treatment. Herein, metallic sulfides (ZnxCd1-xS) with different molar ratio of Zn/Cd were constructed by a facile solvothermal technology and applied to photo-Fenton system as both catalyst and co-catalyst for the first time. The catalytic activity of photo-Fenton systems could be enhanced by adding any as-prepared samples. Moreover, photo-Fenton system containing ZCS-3 (molar ratio of Zn:Cd = 3:7) presented the highest degradation rate for Rhodamine B (RhB, 93.5%), which showed significant improvement compared with that of photo-system without ZCS-3(43.7%). The excellent performance of this photo-Fenton system was mainly ascribed to the synergistic effect between photocatalytic and co-catalytic of ZCS-3. EPR and XPS results confirmed that the Zn2+ in the ZCS-3 would be reduced to Zn+ by the •O2–, which generated under visible light irradiation in photo-Fenton system. Thereby, more Zn+/Zn2+ exposed on the ZCS-3 surface during this photo-Fenton reaction, ensuring the acceleration of conversion between Fe2+ and Fe3+. The catalytic mechanism revealed that the formation of stable double recycles of Zn2+/Zn+ and Fe2+/Fe3+ in catalytic process displayed prominent enhancement for the catalytic properties of the photo-Fenton system.