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,Nd upconversion nanoparticles (UCNP) on effective dye degradation is demonstrated. A detailed characterization of bulk MoS2 (b-MoS2), syn-MoS2 (with enhanced photocatalytic activity compared to the commercially available b-MoS2), and UCNP was done. Optical properties revealed that emission spectra of UCNP corresponding to 450, 475, and 650 nm overlap with absorption spectra of MoS2 (∼455 and 635 nm). A comparative methylene blue degradation of 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 efficiency of 99.6% for 150 mg L–1 of syn-MoS2 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 (•O2–) and hydroxyl (•OH). A comparative photocurrent experiment also verified that the presence of UCNP enhances the efficiency of the syn-MoS2 by 98% in the presence of visible light.