ZnO/ZnS Nanoparticles on NaYF4:Yb,Tm for Near-Infrared-Activated Photocatalytic Cr(VI) Reduction

The essential requirement for photocatalysis-utilization of sunlight energy-was addressed by combining ZnO/ZnS nanoparticles (NPs) with NaYF4:Yb3+,Tm3+ upconversion nanoparticles (UCNPs) in a core-shell composite structure that can convert near-infrared (NIR) light to UV light through energy transfer (ET). The material was examined with advanced characterization techniques and computational methods, which allowed a better understanding of the interface and provided insights into possible conditions for the ET between UCNPs and ZnO, which has not been studied before. In addition, this work suggests a simple method for the in situ formation of a heterojunction on ZnO while it is attached to UCNP, which has not been applied to UCNP-coupled photocatalysts to date. The in situ-formed heterostructure of ZnO and ZnS was proven to enhance NIR-driven photocatalytic activity via efficient charge separation through the Z-scheme mechanism: 70% of Cr(VI) reduction was obtained within 3 h of NIR laser irradiation with UCNP@ZnO/ZnS, while 48% reduction of Cr(VI) was achieved by UCNP@ZnO. Reactive oxygen species (ROS) were detected during NIR-triggered photocatalysis, proving the energy conversion from UCNPsto photocatalysts.

Automated summary

The combination of ZnO/ZnS nanoparticles with NaYF4:Yb3+,Tm3+ upconversion nanoparticles in a core-shell composite structure enables the utilization of sunlight energy in photocatalysis. Advanced characterization techniques and computational methods were used to understand the interface and conditions for energy transfer between upconversion nanoparticles and ZnO. The in situ formation of a heterojunction on ZnO attached to upconversion nanoparticles was also demonstrated to enhance NIR-driven photocatalytic activity.