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

The multishell-structured NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2/Ag@TiO2 (UC@SiO2/Ag@TiO2) nano-spheres 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 vis-ible 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 com-pletely 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.(c) 2023 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Automated summary

The multishell-structured NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2/Ag@TiO2 (UC@SiO2/Ag@TiO2) nano-spheres were prepared for the first time, showing enhanced NIR-triggered photocatalytic activity under the synergistic effect of upconversion and plasmons. The incorporation of Yb/Nd shell significantly improved the upconversion luminescence (UCL) efficiency of NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd upconversion nanophosphors (Yb/Tm/Nd@Yb/Nd UCNPs), and the addition of Ag nanoparticles further enhanced the UCL intensity due to the plasmon resonance effect. The final UC@SiO2/Ag@TiO2 exhibited higher photocatalytic activity and antibacterial activity compared to UC@SiO2@TiO2.