Synergistic Effect of Yb³⁺, Tm³⁺, Nd³⁺ Doped NaYF₄ Nanoparticles and MoS₂ Nanosheets for Enhanced Photocatalytic Dye Degradation under Visible Light

The synergistic influence of synthesized MoS2 (syn-MoS2) nanosheets and NaYF4:Yb,Tm,Ndupconversion nanoparticles (UCNP) on effective dye degradation isdemonstrated. A detailed characterization of bulk MoS2 (b-MoS2), syn-MoS2 (with enhanced photocatalytic activity compared to the commerciallyavailable b-MoS2), and UCNP was done.Optical properties revealed that emission spectra of UCNP correspondingto 450, 475, and 650 nm overlap with absorption spectra of MoS2 (similar to 455 and 635 nm). A comparative methylene blue degradationof 96% could be achieved with the combination of UCNP and syn-MoS2 in comparison to 56.4% for syn-MoS2 and 42% for b-MoS2.Concentration-dependent dye degradation study of UCNP and syn-MoS2 revealed a maximum dye removal efficiencyof 99.6% for 150 mg L-1 of syn-MoS2 and 200 mg L-1 of UCNP within 2 hrs. Comparativedegradation investigations were performed on various dyes (methyleneblue, methylene orange, rhodamine B, and their mixture) and watersystems (artificial river-water and artificial seawater) to assessthe potential applicability of the system in environmental remediation.After five cycles of reusability studies, an efficacy of 88% dye removalwas obtained. The mechanism behind this was investigated using theESR and scavengers test, which confirmed that the primary radicalsresponsible for dye degradation were superoxide (O-center dot(2) (-)) and hydroxyl ((OH)-O-center dot). A comparative photocurrent experiment also verified that thepresence of UCNP enhances the efficiency of the syn-MoS2 by 98% in the presence of visible light.