Enhancement of NIR-triggered photocatalytic activity of Ln3+-doped NaYF4@SiO2/Ag@TiO2 nanospheres through synergistic upconversion and plasmonic effect

Abstract

The multishell-structured NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2/Ag@TiO2 (UC@SiO2/Ag@TiO2) nanospheres were prepared for the first time, which possessed the enhanced NIR-triggered photocatalytic activity under the synergistic effect of upconversion and plasmons. The design of active-core@active-shell structure for NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd upconversion nanophosphors (Yb/Tm/Nd@Yb/Nd UCNPs) significantly improved their upconversion luminescence (UCL) efficiency, which was increased by 12 times after coating a Yb/Nd shell on Yb/Tm/Nd seed crystals via epitaxial growth. After introduction of Ag nanoparticles, the UCL intensity of the obtained UC@SiO2/Ag was further enhanced by 3.3 times compared with the bare UCNPs because the plasmon resonance frequency of Ag overlapped with the visible emission peaks of UCNPs, which permitted an effective surface plasmon-coupled emission, resulting in the increase of emission intensity for UCNPs. Therefore, the final UC@SiO2/Ag@TiO2 could absorb the plasmon-enhanced NIR-to-UV/Vis lights from UCNPs to obtain its photocatalytic activity. Significantly, the photodegradation of Rhodamine B under the action of UC@SiO2/Ag@TiO2 was 26.9 % higher than that under the action of UC@SiO2@TiO2. UC@SiO2/Ag@TiO2 also exhibited a better photocatalytic antibacterial activity against B. subtilis than UC@SiO2@TiO2. In the presence of UC@SiO2/Ag@TiO2, bacteria were completely killed after 15 min of 808 nm NIR illumination. Finally, the possible photocatalytic mechanism of UC@SiO2/Ag@TiO2 was discussed based on the results of scavenger test.