High-performance solar-driven photocatalytic degradation of methylene blue by NaYF4:Yb, Tm@TiO2 core–shell nanostructures

The degradation of persistent organic dyes, such as methylene blue (MB), is crucial for protecting aquatic environments, as these compounds are chemically stable and resistant to conventional treatment methods. The TiO 2 -based photocatalysts have been widely explored for pollutant degradation owing to their chemical robustness, eco-friendliness, and strong oxidative capability under light irradiation. However, its wide bandgap (∼3.0–3.2 eV) restricts optical absorption to the ultraviolet region, which comprises only a small portion, less than 5 % of solar energy. In this work, a UCNRs@TiO 2 core–shell nanostructured photocatalyst composed of NaYF 4 :30 Yb 3+ ,0.5 Tm 3+ upconversion nanorods (UCNRs) and TiO 2 nanoparticles was successfully fabricated to enhance both ultraviolet (UV) and near infrared (NIR)-responsive photocatalytic activity. The UCNRs serve as efficient optical converters, absorbing near-infrared light at 980 nm and emitting UV photons to activate TiO 2 , thereby extending its operational spectral range. Photocatalytic activity was evaluated under solar simulated irradiation by monitoring the degradation of MB at a concentration of 15 mg/L. The UCNRs@TiO 2 photocatalyst achieved a remarkable degradation efficiency of 100 % MB within 90 min with an apparent rate constant of 0.063 min −1 , in contrast to 195 min required by bare TiO 2 . In addition, the photocatalytic enhancement mechanism of UCNRs@TiO 2 materials was also proposed based on the results of Photoluminescence, UV–Vis spectra and LC-MS. The excellent stability of the composites after three cycles of reuse demonstrates their promise for the rational design of NIR-driven photocatalysts for sustainable wastewater treatment.