Construction of a direct Z-scheme ZnS quantum dot (QD)-Fe2O3 QD heterojunction/reduced graphene oxide nanocomposite with enhanced photocatalytic activity

A novel direct Z-scheme ZnS quantum dot (QD)-Fe2O3 QD heterojunction/reduced graphene oxide (rGO) (GZxFy) nanocomposite was successfully synthesized by a simple hydrothermal method. The surface of ZnS and Fe2O3 QDs was modified by COOH and OH groups, respectively. ZnS QDs can be covalently bonded with Fe2O3 QDs by the dehydration reaction to form the ZnS QDs-Fe2O3 QDs heterojunctions. The GZxFy nanocomposites displayed the highest photodegradation efficiency of 96.45% (40 min, UV light) and 90.17% (480 min, visible light) for methylene blue when the mass ratio of ZnS QDs to Fe2O3 QDs was 1:3. The excellent photocatalytic activity could be attributed to the enhanced light-harvesting ability, high large specific surface area, efficient interfacial charge-carrier separation and transfer as well as the low charge transfer resistance. Ultraviolet photoelectron spectroscopy and radical trapping experiments were used to confirm the Z-scheme mechanism formed between ZnS QDs and Fe2O3 QDs, and verify the electron transfer direction for UV or visible light-driven photocatalytic reactions. GZ1F3 nanocomposites showed the excellent superparamagnetic behavior, which enabled its rapid magnetic recycle from the solution within 95 s in a magnetic field.