Enhanced TiO<sub>2</sub> Broadband Photocatalytic Activity Based on Very Small Upconversion Nanosystems
Maryam Sadat Ghorashi, Hamid Reza Madaah Hosseini, Ezeddin Mohajerani, Marco Pedroni, Reza Taheri Ghahrizjani
Abstract
Efficient sunlight harvesting is of great significance for environmental remediation through photocatalysis. Herein, very small (20 nm) upconverter SrF2:Yb,Tm@CaF2:Yb@Fluorine-doped TiO2 heteronanoparticles (denoted as UCNPs@TiO2) with strong UV-blue emission and broadband photocatalytic performance were prepared via a facile three-step hydrothermal method for the first time. The SrF2:Yb,Tm upconverter nanoparticles (NPs) were produced as the light-emitting core, epitaxially grown CaF2:Yb as the middle shell to enhance the upconversion luminescence output and TiO2 as the photocatalyst outermost layer. Superior photocatalytic functioning of UCNPs@TiO2 was affirmed through methylene blue (MB) degradation under illumination by 980 nm laser light and different bands of simulated solar light, referring to TiO2 P25. This study authenticates that the visible and NIR bands of simulated solar light could stimulate proper photocatalytic performance in the presence of UCNPs@TiO2 due to F-doping of TiO2 and upconversion nanoparticle (UCNP) integration, respectively. Furthermore, the efficacious reactive oxygen species (ROS) generation ability of UCNPs@TiO2 was verified under NIR light, suggesting their applicability as photodynamic therapy (PDT) agents. The resulting heteronanoparticles hold the privileges of wide-spectrum-light harvesting, effective energy transfer between constituent upconversion core and TiO2 layer, and reduced electron–hole recombination, indicating their strong potential applications in photocatalysis, solar cells, and PDT.