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 MoS<inf>2</inf> (syn-MoS<inf>2</inf>) nanosheets and NaYF<inf>4</inf>:Yb,Tm,Nd upconversion nanoparticles (UCNP) on effective dye degradation is demonstrated. A detailed characterization of bulk MoS<inf>2</inf> (b-MoS<inf>2</inf>), syn-MoS<inf>2</inf> (with enhanced photocatalytic activity compared to the commercially available b-MoS<inf>2</inf>), and UCNP was done. Optical properties revealed that emission spectra of UCNP corresponding to 450, 475, and 650 nm overlap with absorption spectra of MoS<inf>2</inf> (∼455 and 635 nm). A comparative methylene blue degradation of 96% could be achieved with the combination of UCNP and syn-MoS<inf>2</inf> in comparison to 56.4% for syn-MoS<inf>2</inf> and 42% for b-MoS<inf>2</inf>. Concentration-dependent dye degradation study of UCNP and syn-MoS<inf>2</inf> revealed a maximum dye removal efficiency of 99.6% for 150 mg L^-1 of syn-MoS<inf>2</inf> and 200 mg L^-1 of UCNP within 2 hrs. Comparative degradation investigations were performed on various dyes (methylene blue, methylene orange, rhodamine B, and their mixture) and water systems (artificial river-water and artificial seawater) to assess the potential applicability of the system in environmental remediation. After five cycles of reusability studies, an efficacy of 88% dye removal was obtained. The mechanism behind this was investigated using the ESR and scavengers test, which confirmed that the primary radicals responsible for dye degradation were superoxide (^•O<inf>2</inf>^-) and hydroxyl (^•OH). A comparative photocurrent experiment also verified that the presence of UCNP enhances the efficiency of the syn-MoS<inf>2</inf> by 98% in the presence of visible light.