Plasmonic-enhanced photocatalytic activity in Ln3+-doped NaYF4@SiO2@TiO2/Ag core/shell nanospheres with NIR light response characteristics

To enhance the photoresponse range and photocatalytic activity of the wide-bandgap semiconductor TiO2, we attempted to integrate TiO2 with NaYF4-based upconversion nanoparticles (UCNPs) and plasmonic metal particles to construct NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd@SiO2@TiO2/Ag (UC@SiO2@TiO2/Ag) core/shell nanospheres with NIR photoresponse characteristics. These nanospheres were synthesized by depositing a TiO2/Ag shell on the UC@SiO2 support through a one-step co-deposition method. NaYF4:Yb,Tm,Nd@NaYF4:Yb,Nd (Yb/Tm/Nd@Yb/Nd) UCNPs designed with an active-core/active-shell structure can generate higher luminescence output through the cascade-sensitized UC process than the core-only structured Yb/Tm/Nd, thereby improving the fluorescence resonance energy transfer between UCNPs and the semiconductor photocatalyst. From the photocatalytic dye degradation and antibacterial experiments, we can see that UC@SiO2@TiO2/Ag exhibited better NIR-responsive photocatalytic activity than UC@SiO2@TiO2 control group, which was achieved through the synergistic effect between energy transfer upconversion in UCNPs and surface plasmon resonance (SPR) of Ag nanoparticles (AgNPs). Furthermore, the Schottky barrier at TiO2/Ag interface suppressed the combination of photogenerated electron-hole pairs, enabling more of them to effectively react with adsorbed O2 and water molecules on the catalyst surface to produce reactive oxygen species (ROS). Based on the radical scavenger test, we confirm that superoxide (•O2−) and hydroxyl (•OH) radicals played primary and secondary roles, respectively, in the oxidative antibacterial process. The possible working mechanism of UC@SiO2@TiO2/Ag was fully discussed, which can help us optimize the design and photochemical performance of this type of core/shell structured ternary photocatalysts composed of UCNPs, semiconductors, and noble metals. [Display omitted] •UC@SiO2@TiO2/Ag nanospheres were prepared via a one-step co-precipitation method.•UC@SiO2@TiO2/Ag exhibits better NIR-driven photocatalytic activity than UC@SiO2@TiO2.•The activity is due to the synergistic effect between ETU in UCNPs and SPR of AgNPs.•The Schottky barrier at the TiO2/Ag interface suppresses the carrier recombination.