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

Abstract

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.