Quantum Dot Supraparticle Photocatalysts for Photodegradation of Rhodamine B

Metal oxide nanomaterials, such as TiO₂, are extensively utilized in photocatalysis for applications, including water purification, antibacterial disinfection, and energy harvesting. However, the wide bandgap (∼3.2 eV) of TiO₂ constrains excitation to UV light, limiting its efficiency under solar irradiation. To extend photocatalytic activity into the visible spectrum, colloidal semiconductor quantum dots (QDs) can function either as independent photocatalysts or as sensitizers; in the latter case, facilitating charge transfer to TiO₂ and enhancing reactive oxygen species (ROS) generation. Here, we demonstrate a photocatalytic platform, composed of QD supraparticles (SP), optionally coated with a titania shell. This hierarchical SP architecture bridges the electronic and photonic scales, significantly enhancing light-harvesting efficiency compared to conventional QDs or metal oxide nanocrystals. The photocatalytic performance of these QD-based SPs is systematically evaluated under both UV and white light illumination, using rhodamine B (RhB) degradation as a model reaction, and compared to QDs and TiO₂ nanoparticles. We find that SPs facilitate both RhB degradation and N-deethylation, with titania-coated SPs (SP/TiO₂) achieving full transformation to Rhodamine 110. We also show that for QDs and SPs with comparable overall surface area, SPs degrade RhB much faster under both UV and white light irradiation. In addition, the reusability of the QD-based SPs is dramatically improved compared to that of QDs. These findings demonstrate the strong potential of QD-based SPs as photocatalytic materials for environmental, energy, chemical, and biomedical applications.