A plasmonic heterojunction for full-spectrum light harvesting and photoinduced charge storage: NaYF 4 :Yb,Tm@TiO 2 /Fe 3 O 4 /Au for environmental remediation

The practical application of photocatalysts in environmental remediation remains constrained by insufficient solar-spectrum utilization, rapid photogenerated charge recombination, and loss of catalytic activity under dark conditions. Herein, we report a multifunctional NaYF₄:Yb, Tm@TiO₂/Fe₃O₄/Au (NTFA) S-scheme nanoheterojunction designed to address these limitations through integrated full-spectrum light harvesting, plasmon-enhanced charge separation, and charge-storage-assisted catalysis. The NaYF₄:Yb, Tm upconversion nanoparticles extend photoresponse into the near-infrared region, Au nanoparticles introduce localized surface plasmon resonance to enhance light absorption and interfacial charge transfer, and Fe₃O₄ serves as an electron-trapping and storage component. This synergistic architecture provides a measurable photoresponse across UV, visible, and near-infrared photons while suppressing electron–hole recombination and sustaining catalytic reactions after light irradiation ceases. With optimized Au loading, NTFA-4 achieved 94.1% degradation of malachite green, markedly outperforming conventional photocatalysts. Notably, its charge-storage capability enabled continued pollutant degradation under dark conditions, demonstrating potential for overcoming intermittency in solar-driven water treatment. In municipal wastewater, NTFA-4 removed 94.3% of malachite green and 73.6% of ammonia nitrogen, confirming its effectiveness in complex aqueous matrices. This work provides a rational strategy for constructing multifunctional photocatalytic heterojunctions with extended spectral response, enhanced charge dynamics, and persistent catalytic activity for sustainable wastewater remediation.