Optimized design and mechanistic understanding of plasmon and upconversion enhanced broadband photocatalysts

Abstract

Abstract A series of core@shell particles composed of upconverting NaYF4: Yb3+/Er3+/Tm3+ cores with different Tm3+:Er3+ molar ratios and porous TiO2 shells loaded with Au nanoparticles (NPs) (altogether denoted as NYF@TiO2-Au) were designed and synthesized. The emissions upconverted from near-infrared (NIR) to ultraviolet (UV), blue and green regions were tuned by varying the doping ratio of Tm3+:Er3+ in NYF. The quenching of UV emissions in samples involving TiO2 and the quenching of green emissions with Au loading suggest the energy transfer from NYF to TiO2 and to Au NPs, respectively. In the photocatalytic degradation of methyl orange (MO), all the prepared NYF@TiO2-Au samples show greatly enhanced photocatalytic activities under UV, visible, and NIR irradiation. In terms of NIR-photocatalytic activity, the optimized doping ratio of Tm3+:Er3+ was found to be 6:0, leading to the highest MO removal rate of 84% within 20 h of NIR irradiation. The contribution of NYF-to-TiO2 energy transfer was about 3 times higher than that of NYF-to-Au energy transfer in the NIR-photocatalysis, which was confirmed by the performed control experiments. This work provides guidelines for the rational design of efficient broadband photocatalysts involving upconversion materials, and offers physical insights into the energy transfer processes in plasmon and upconversion enhanced photocatalysis.