Effect of shell structure on the photocatalytic activity of UCNPs/NMC: comparison among inert and active shells

Inefficient utilization of the solar spectrum remains a major limitation in photocatalysis. To address this, we developed a photocatalyst by combining upconversion nanoparticles (UCNPs) with NH₂-MIL-101(Cr) (NMC), leveraging the use of the broad photoresponsive range from the ultraviolet-visible (UV-vis) to the near-infrared (NIR) region. Despite the potential of UCNPs, their photocatalytic performance is often hindered by surface quenching, which reduces emission intensity. The incorporation of various shells is a popular and feasible pathway to solve this issue. However, there are limited studies that compare the influence of different shells under the same conditions. In this work, four core-shell UCNPs with distinct shell compositions were designed and integrated with NMC to investigate the impact of shell structure on photocatalytic activity. Among these, Tm@Y/NMC displayed the highest photocatalytic activity in decomposing rhodamine B (RhB) due to its strongest emission intensity and extended photoresponsive range. The photocatalytic activity of other samples was inferior to that of Tm@Y/NMC, indicating the superiority of the inert shell. Based on the results of trapping experiments and analysis of various spectral properties, we proposed a plausible photocatalytic mechanism. The findings of this study are helpful to guide the structural refinement of photocatalysts, thereby developing photocatalysts with more effective and robust performance.