Composites of YF₃: Yb³⁺, Er³⁺, Tm³⁺@C₃N₄-Au with near-infrared light-driven ability for photocatalytic wastewater purification

Photocatalytic technology for removing organic dye pollutants has gained considerable attention because of its ability to harness abundant solar energy without requiring additional chemical reagents. In this context, YF₃ spheres doped with Yb³⁺, Er³⁺, Tm³⁺ (YF) are synthesized using a hydrothermal method and are subsequently coated with a layer of graphitic carbon nitride (g-C₃N₄) with Au nanoparticles (NPs) adsorbed onto the surface to create a core-shell structure, designated as YF₃: Yb³⁺, Er³⁺, Tm³⁺@C₃N₄-Au (abbreviated as YF@CN-Au). The core-shell composites demonstrate remarkable stability, broadband absorption, and exceptional photocatalytic activity across the ultraviolet (UV) to near-infrared (NIR) spectral range. Notably, by optimizing the amount of Au loaded, excellent methyl orange (MO) degradation rates of 0.068 min^-1 under UV light and 0.423 h^-1 under light excitation with <i>λ</i> > 420 nm can be achieved. Even under low-energy NIR light (<i>λ</i> > 800 nm), a degradation rate of 0.087 h^-1 was reached, indicating a significantly enhanced degradation effect compared to YF@CN without Au loading. The high performance of the core-shell composite is attributed to its unique structure, which enables efficient transfer of energy and charge carriers, thereby promoting charge separation and suppressing recombination. Furthermore, this article reveals and discusses three distinct photocatalytic mechanisms under UV, visible, and NIR light. This study underscores the considerable promise of core-shell composites in developing efficient g-C₃N₄-based broadband photocatalysts, focusing on comprehensive utilization of the solar spectrum through the synergistic effects of plasma and upconversion materials.