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

Abstract

The synergistic influence of synthesized MoS 2 ( syn -MoS 2 ) nanosheets and NaYF 4:Yb,Tm,Nd upconversion nanoparticles (UCNP) on effective dye degradation is demonstrated. A detailed characterization of bulk MoS 2 ( b -MoS 2 ), syn -MoS 2 (with enhanced photocatalytic activity compared to the commercially available b -MoS 2 ), 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 2 (∼455 and 635 nm). A comparative methylene blue degradation of 96% could be achieved with the combination of UCNP and syn -MoS 2 in comparison to 56.4% for syn -MoS 2 and 42% for b -MoS 2 . Concentration-dependent dye degradation study of UCNP and syn -MoS 2 revealed a maximum dye removal efficiency of 99.6% for 150 mg L –1 of syn -MoS 2 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 2 – ) and hydroxyl ( • OH). A comparative photocurrent experiment also verified that the presence of UCNP enhances the efficiency of the syn -MoS 2 by 98% in the presence of visible light.