Rational Design and Development of Lanthanide-Doped NaYF₄@CdS–Au–RGO as Quaternary Plasmonic Photocatalysts for Harnessing Visible–Near-Infrared Broadband Spectrum

Utilization of the total solar spectrum efficiently for photocatalysis has remained a huge challenge for a long time. However, designing a system by rationally combining nanocomponents with complementary properties, such as upconversion nanoparticles, semiconductors, plasmonic metals, and carbonaceous support, offers a promising route for efficient utilization of solar energy by harnessing the broadband spectrum. In this work, a series of novel quaternary plasmonic photocatalysts comprising of lanthanide-doped NaYF₄@CdS (UC) core–shell nanostructures decorated with Au nanoparticles (Au NPs) supported on reduced graphene oxide (RGO) nanosheets were prepared using the multistep hydrothermal method. The different components of the prepared nanocomposites could be efficiently employed to utilize both the visible and near-infrared (NIR) regions. Specifically in this work, the utility of these quaternary nanocomposites for photocatalytic degradation of a colorless pharmaceutical pollutant, ciprofloxacin, under visible and NIR light irradiations has been demonstrated. In comparison to bare counterparts, our quaternary nanocomposites exhibit an enhanced photocatalytic activity attributable to the synergistic effect of different components arranged in such a way that favors harnessing energy from the broad spectral region and efficient charge separation. The combination of upconversion and plasmonic properties along with the advantages of a carbonaceous support can provide new physical insights for further development of photocatalysts, which could utilize the broadband spectrum.